Long-Term Fertility Function Sequelae in Young Male Cancer Survivors

Abstract

With advances in cancer treatment, such as cytotoxic chemotherapy and radiotherapy, grave new sequelae of treatment have emerged for young cancer survivors. One sequela that cannot be overlooked is male infertility, with reportedly 15% to 30% of cancer survivors losing their fertility potential. Cytotoxic therapy influences spermatogenesis at least temporarily, and in some cases, permanently. The degree of spermatogenesis impairment depends on the combination of drugs used, their cumulative dose, and the level of radiation. The American Society of Clinical Oncology has created an index to classify the risks to fertility based on treatment. Medical professionals currently use this risk classification in fertility preservation (FP) programs. FP programs are currently being promoted to prevent spermatogenesis failure resulting from cancer treatment. For patients who are able to ejaculate and whose semen contains sperm, the semen (sperm) is cryopreserved. Moreover, for patients who lack the ability to ejaculate, those with azoospermia or severe oligozoospermia, and those who have not attained puberty (i.e., spermatogenesis has not begun), testicular biopsy is performed to collect the sperm or germ cells and cryopreserve them. This method of culturing germ cells to differentiate the sperm has been successful in some animal models, but not in humans. FP has recently gained popularity; however, some oncologists and medical professionals involved in cancer treatment still lack adequate knowledge of these procedures. This hinders the dissemination of information to patients and the execution of FP. Information sharing and collaboration between reproductive medicine specialists and oncologists is extremely important for the development of FP. In Japan, the network of clinics and hospitals that support FP is expanding across prefectures.

INTRODUCTION

The incidence of malignant tumors in Japanese young men is 86.2 in 100,000 adolescents and young adults, affecting approximately 7,600 people per year [1]. Katanoda et al [2] investigated the incidence of malignant disease among young people in Japan from 2009 to 2011. Per million population, there were 120.2 aged 0–14 years, 130.5 aged 15–19 years, 229.0 aged 20–29 years, and 537.3 males aged 30–39 years. This data was similar to that of the United States and World data (World Health Organization) [2]. As in other developed countries, advances in treatment have significantly improved outcomes for young patients with cancer. For advanced testicular cancer, the 3-year survival rates for good-, intermediate-, and poor-risk patients are 94.7%, 94.2%, and 74.3%, respectively [3]. As of 2017, the 5-year survival rate for bone and soft tissue tumors was 71.8% for children and 73.1% for young people (15–29 y) [4]. According to a 2014 National Cancer Center survey, the 10-year relative survival rates for leukemia, malignant lymphoma, and brain tumors were 76.5%, 88.6%, and 58.0%, respectively, for persons aged 0–14 years, and 52.5%, 73.4%, and 58.9%, respectively, for those aged 15–29 years [5].

Cancer survivors play an active role in society. After overcoming their illnesses, many want to live their lives in the same way as healthy individuals. A questionnaire survey of male patients with cancer indicated that half of them wanted to be fathers in the future [6], have a family, and be a good parent [7].

Unlike cancer in the elderly, the diagnosis, treatment, and follow-up for cancer in young patients occur during major life events, such as school attendance, employment, marriage, childbirth, and child-rearing. Moreover, even if the disease is cured, the patient experiences late complications (sequelae) of treatment over a long period, since the age of onset is young. Decreased fertility is one of the sequelae of cancer. Some patients may give up getting married or having a partner, or may be forced to make major changes to their life plans because they cannot conceive. Others may be concerned that the health of their children will be compromised by the treatments they receive. Benedict et al [8] conducted a questionnaire survey on fertility, with 43 men and women who had cancer during their adolescent and young adult years. Their responses indicated that 50% of the men and 39% of the women were concerned about fertility uncertainty. Therefore, the negative sequelae of reduced fertility threaten the future of patients with cancer. With the development of numerous therapeutic tools and agents and advances in surgical devices, the treatment outcomes of young patients with cancer have improved. As a next step, it is important to determine the causes of these infertility sequelae, establish appropriate fertility treatment methods, develop effective prevention methods (fertility-preserving treatment), and study the impact of medical care on the offspring of survivors to renew the hope for future progeny of cancer survivors.

MALE INFERTILITY CAUSED BY CANCER TREATMENT

The causes of male infertility are generally classified as follows: (1) testicular dysfunction/the testes cannot produce sufficient sperm; (2) obstruction or defects of the seminal tract; (3) sexual dysfunction, such as erectile dysfunction (ED)/ejaculation disorder [9]; (4) and hypogonadism because of gonadotropin secretion decrease followed by impairment of spermatogenesis due to radiation therapy to the brain, tumor restriction for CNS tumors, total or partial orchiectomy [10]. In addition, a decrease in gonadotropin secretion also occurs with pituitary inflammation caused by immune checkpoint inhibitors, such as nivolumab [11]. The causes of the infertility that commonly occur after cancer treatment may also be classified into these four groups (Fig. 1).

Fig. 1. Classification of male infertility caused by cancer treatment. LH: luteinizing hormone, FSH: follicle stimulating hormone.

Testicular dysfunction after chemotherapy or radiation therapy is currently the most problematic sequela of cancer treatment and an important long-term sequela for young cancer survivors. Schrader et al [12] reviewed reports examining the effect of chemotherapy on sperm concentration in adult men with testicular germ cell cancer and lymphoma. As a result, they reported that 15% to 30% of male cancer survivors lost fertility potential [12]. Patients with cancer exhibit poor semen analysis results. According to Chung et al [13], 28%, 25%, 57%, and 33% of patients with testicular cancer, Hodgkin’s disease, leukemia, and gastrointestinal cancers, respectively, have oligozoospermia. Moreover, among the patients who have undergone sperm banking (SB), 50% reportedly have a sperm count of 10 million [14]. Approximately 5% to 11% of patients that visit the hospital for SB have azoospermia [15,16,17]. Patients with cancer have a poor nutritional status, which leads to vitamin and electrolyte deficiencies, increased cytokine levels, and endocrine system abnormalities; the decrease in the observed sperm count may be attributable to these factors [18,19,20]. However, these deficiencies may not improve after the cancer treatment is completed.

Furthermore, azoospermia and aspermia may occur when the vas deferens is cut and the seminal vesicles and prostate are removed after a total prostatectomy or cystectomy. Retroperitoneal lymph node dissection for testicular cancer and surgery for malignant tumors in the pelvis may result in severing of the nerves involved in ejaculation, resulting in anejaculation or retrograde ejaculation [21,22]. Patients who have undergone radical prostatectomy may develop ED if the neurovascular bundle is amputated [23]. Bilateral orchiectomy for bilateral testicular cancer causes permanent azoospermia [23] and penile amputation can make sexual intercourse difficult for patients with penile cancer [24]. Furthermore, recent studies have shown that reactive oxygen species are detected in the semen of 42% of the patients treated with anticancer drugs. It has been suggested that oxidative stress persists for a long time, even after the cancer treatment is completed [25].

Wasilewski-Masker et al [26] conducted a questionnaire survey on infertility among 1,622 male cancer survivors and their 264 siblings. The incidence of infertility in the cancer survivor cohort was 46.0%, whereas that in the sibling cohort was 17.5% (risk ratio=2.34, 95% confidence interval=1.88–3.70, p<0.001) [26]. In developed countries, the incidence of infertility, in general, is approximately 15%, which is similar to that in the abovementioned sibling cohort [27]. Additionally, in the abovementioned cancer survivor cohort [26], 12 survivors underwent surgical excision of any organ of the genital tract and reported infertility, and five survivors reported infertility after undergoing surgical procedures on the spinal cord/canal or sympathetic nerves. Therefore, unlike normal male infertility, most cases of infertility caused by cancer treatment are due to the gonadotoxic effects of anticancer drugs or radiation therapy. A review by Delessard et al [28] also states that chemotherapy exposure during adulthood and childhood causes a deterioration in semen quality, an increase in sperm DNA fragmentation (SDF), and a decrease in birth rate due to these factors. It is evident that saving the lives of patients is the highest priority during cancer treatment; however, it is also important for medical professionals to predict and respond to the risk of potential infertility in the future.

MECHANISM OF SPERMATOGENESIS AND DECREASE IN SPERMATOGENIC ABILITY DUE TO CHEMOTHERAPY/RADIOTHERAPY

Spermatogenesis is a collection of complex processes that occur in the seminiferous tubules, beginning with the proliferation of germ cells. Spermatogonia are the germ cells that are the source of sperm and are located between the Sertoli cells at the basement membrane of the seminiferous tubules toward the lumen. When the number of spermatogonia decreases, they undergo mitosis. The number of germ cells stays relatively constant through self-proliferation. Some spermatogonia undergo spermatogenesis via meiosis [29]. Blood vessels do not directly enter the seminiferous tubules; thus, the substances required for spermatogenesis are taken up by the Sertoli cells from around the seminiferous tubules and transported to the germ and sperm cells. The blood-testis barrier, which is located between the Sertoli cells [29], prevents harmful substances from invading the germ and Sertoli cells. However, there are several drugs, including anticancer agents, that can pass through the blood-testis barrier (Fig. 2) [30]. For example, animal experiments have reported that the alkylating agents, ethyl methanesulphonate and imatinib, readily penetrate the blood-testis barrier [31,32].

Fig. 2. Internal structure of the seminiferous tubule.

Spermatogonia are extremely sensitive to the cytotoxic effects of radiation and anticancer drugs. This susceptibility is increased in the spermatogonia undergoing differentiation [33]. However, late-stage germ cells are relatively resistant to the cytotoxic effects of cancer therapy. Therefore, although the number of spermatogonia decreases after cancer treatment, spermatogenesis still occurs in the late-stage germ cells (spermatocytes and spermatids). Although the sperm count does not significantly change immediately after the start of treatment, it drops dramatically from 1/10 to 1/100 of the normal number within 1 to 2 months after the start of treatment. Azoospermia may occur 12 weeks after initiating the treatment, depending on the toxicity, the dosage, and the combination of the agents [34]. However, not all treated cases of cancer result in infertility. Some patients showed normal semen quality after cancer treatment and had children without undergoing treatment for infertility. In cases of cancer treatment using an agent with a low cell-killing effect, the sperm count usually returns to normal approximately 12 weeks after the discontinuation of chemotherapy [34]. However, in cases of treatment using an agent with a high cell-killing effect, the recovery of spermatogenesis, the duration until recovery, and the degree of recovery depend on the number of stem cells remaining after the treatment [34], which in turn depends on the type of agent used, the treatment regimen, and the dose administered. For example, alkylating agents, such as cyclophosphamide and ifosfamide, are highly toxic to the testis. It has been said that regimens containing these agents have strong testicular toxicity. For example, the total dose of cyclophosphamide is 19 g/m² when used as a single agent and >7.5 g/m² when combined with multiple agents. A dose of ifosfamide higher than 42 g/m² reportedly increases testicular damage [35]. A total cisplatin dose of 400 mg/m² also increases the risk of azoospermia [33]. However, previous studies have provided less accurate evidence regarding agent dose [36]. In recent years, rather than regimen-based risk classification, risk classification based on the cumulative dose of drugs has become mainstream (Table 1) [28,37,38,39]. Green et al [40] converted the dose of the alkylating agent to a cyclophosphamide equivalent dose (CED). Administration of drugs with a CED of 4,000 mg/m² or more is highly likely to cause azoospermia, and above this dose was defined as high dose, and below this dose was defined as low dose [40]. In this way, the risk classification of anticancer agents has changed significantly in recent years. Therefore, oncologists and reproductive medicine specialists in charge of fertility preservation (FP) should be careful.

Table 1. Risk classification for currently reported effects of different anti-tumor agents or radiation therapy on sperm production.

Risk classification	ASCO (2013) [38]	Delessard et al (2020) [28]	ESMO (2020) [39]	Delgouffe et al (2022) [37]
High risk	Any alkylating agent+TBI Any alkylating agent+pelvic or testicular radiation Total cyclophosphamide >7.5 g/m2 Protocol containing procarbazine: MOPP >3 cycles, BEACOPP >6 cycles Protocol containing temozolomide or BCNU+cranial radiation	Chlorambucil 1.4 g/m2 (child) Cyclophosphamide 19 g/m2 (child and adult, 7.5 g/m2) Procarbazine 4 g/m2 (child) Melphalan 140 mg/m2 (child) Cisplatin 500 mg/m2 (child) Busulfan 600 mg/m2 (child) Ifosfamide 4 g/m2 (child)	TBI	Busulfan >600 mg/m2 Carmustine 1 g/m2 Chlorambucil >1.4 g/m2 Chlormetine (undetermined dose) Cisplatin >600 mg/m2 Cyclophosphamide >19 g/m2 Ifosfamide >52 g/m2 Lomustine 500 mg/m2 (If treated before puberty) Mechlorethamine (undetermined dose) Melphalan >140 mg/m2 Mustine (undetermined dose) Procarbazine >4 g/m2
			Testicular radiation: germ cell >20 Gy in men, somatic cell >30 Gy Alkylating agent (cyclophosphamide, ifosfamide, procarbazine, cisplatin, chlorambucil, carmustine, lomustine, melphalan, thiotepa, busulfan, mechlorethamine) with CED >5 g/m2 for germ cell, 20 g/m2 for somatic cell
	TBI		Conditioning chemotherapy for radiotherapy (busulfan, cyclophosphamide, fludarabine, melphalan)	TBI
	Cranial radiation >40 Gy			Testicular radiation
	Testicular radiation >2.5 Gy in men, >6 Gy in boys
Intermediate (medium, moderate) risk	BEP >2–4 courses Total cisplatin >400 mg/m2 Total carboplatin >2 g/m2	Ifosfamide 42 g/m2 (adult) Carboplatin 2 g/m2 (child) Thiotepa 400 mg/m2 (child) Doxorubicin 770 mg/m2 (child) Cytarabine 1 g/m2 (child) Dacarbazine (child) Daunorubicin (child) Mitoxantrone (child)	Alkylating agent (thiotepa, cisplatin <0.6 g/m2, oxaliplatin, carboplatin, dacarbazine) Anthracyclines (doxorubicin, idarubicin, daunorubicin) Mitoxantrone Antimetabolites (cytarabine , gemcitabine)	Carboplatin >2 g/m2 Cisplatin >400–600 mg/m2 Cyclophosphamide >7.5–19 g/m2 Cytarabine 1 g/m2 Dacarbazine (undetermined dose) Daunorubicin (undetermined dose) Doxorubicin >770 mg/m2 Gemcitabine (undetermined dose) Ifosfamide 42–52 g/m2 Mitoxantrone (undetermined dose) Oxaliplatin (undetermined dose) Thiotepa 400 mg/m2 Cranlospinal-and cranial radiotherapy ≥25 Gy Scattered abdominal or pelvic radiation ≥1 Gy
Lower (low) risk	Protocol containing nonalkylating agents; ABVD,CHOP Antracycline+cytarabine	Vinblastine 50 g/m2 (child) Vincristine 8 g/m2 (child) Bleomycin (child) Etoposide (child) Fluorouracil (child) Mercaptopurine (child) Methotrexate (child)	Antimetabolites (mercaptopurine, methotrexate, fludarabine) Tubulin-binding agents/vinca alkaloids (vinblastine, vincristine) Topoisomerase inhibitor (etoposide) Antitumour antibiotics (bleomycin, dactinomycin, mitomycin C)	Actinomycin-D (undetermined dose) Azathioprine (undetermined dose) Bleomycin (undetermined dose) Cytarabine <1 g/m2 Dactinomycin (undetermined dose) Etoposide (undetermined dose) Fludarabine (undetermined dose) 5-Fluorouracil (undetermined dose) 6-Mercaptopurine (undetermined dose) Methotrexate (undetermined dose) Vinblastine 50 g/m2 Vincristine 8 g/m2
	Testicular radiation <0.2–0.7 Gy			Lower radiation dose
Very low risk	Multi-agent therapies containing vincristine Radioactive iodine Testicular radiation (due to scatter) <0.2 Gy
Unknown	Monoclonal antibodies Tyrosine kinase inhibitors	Fludarabine Thioguanine	Antimetabolites (fluorouracil, thioguanine) Taxanes (paclitaxel, docetaxel) Topoisomerase inhibitors (irinotecan, topotecan, teniposide) Immunotherapy Targeted therapies (monoclonal antibodies, small molecules)

High risk: prolonged or permanent azoospermia is common after treatment. Intermediate (medium, moderate) risk: prolonged or permanent azoospermia is not common after treatment but can occur. Lower (low) risk: treatments typically cause only temporary damage to sperm production. Very low risk: no effect on sperm production.

ABVD: adriamycin, bleomycin, vinblastine, dacarbazine, ASCO: American Society of Clinical Oncology, BCNU: bis-chloroethylnitrosourea, BEACOPP: bleomycin, etoposide, hydroxydaunorubicin (adriamycin), cyclophosphamide, oncovin (vincristine), procarbazine, prednisone, BEP: bleomycin, etoposide, cisplatin, CED: cyclophosphamide equivalent dose, CHOP: cyclophosphamide, hydroxydaunorubicin (adriamycin), oncovin (vincristine), prednisone, ESMO: European Society for Medical Oncology, MOPP: mechlorethamine, oncovin (vincristine), procarbazine, prednisone, TBI: total body irradiation.

Upon treatment with radiation therapy, spermatogonia begin to decrease at approximately 21 weeks after a single irradiation of 0.2–0.4 Gy; at this point, differentiation into spermatocytes also decreases [41,42]. When the testicular radiation dose is over 0.1 Gy, impairment of spermatogenesis starts to occur [43]. However, it should be noted that the sperm count may not return to its original number after irradiation dose 1.2 Gy, even if recovery is observed [35,44]. In boys, cases of permanent infertility appear when the irradiation dose to the testes exceeds 4.0 Gy [43]. Only 15% of adult patients recover fertility after a single irradiation dose of 10 Gy [34]. When the dose exceeds 16–18 Gy, 95% of patients demonstrate complete germ cell destruction [45]. Fractionated irradiation is effective for the treatment of cancer and reduces damage to the irradiated area; however, the resulting damage to the testes is large. Additionally, cumulative doses to the testes above 2.5 Gy can lead to irreversible azoospermia [35,44]. In their study of 11 patients with rectal cancer (mean age, 55.2 y) who were administered 50 Gy of intrapelvic irradiation, Hermann et al [46] reported that irradiation of 3.56 Gy to the testes increased the risk of permanent infertility and hypogonadism. The combined damage caused by antineoplastic agents and radiation therapy is significant, with 83% of patients having permanent azoospermia due to total body irradiation and cyclophosphamide administration prior to stem cell transplantation for leukemia [47]. Cranial radiation does not directly affect the testis, but the hypothalamic-pituitary-gonadal axis is disturbed, and gonadotropin secretion is reduced, which reduces spermatogenesis and fertility [36]. Although fertility may be restored by supplementation with gonadotropin after treatment, FP should be done because there is a risk of cancer recurrence [36]. Unlike anticancer drugs, there is not much difference in the risk classification of radiation according to literature (Table 1).

In recent years, the use of molecular targeting agents, such as tyrosine kinase inhibitors, in cancer treatment has been increasing. These agents target the molecules involved in the growth of cancer cells and suppress cell proliferation signals to inhibit the proliferation of cancer cells. In a review, Wyns et al summarized the impact of targeting agents, which have been approved by the U.S. Food and Drug Administration (FDA) in recent years (Table 2) [48]. Although little information is available on the association between these agents and fertility, sperm cells express tyrosine kinase proteins involved in meiosis, capacitation, and acrosome reactions [49]. Since there is no data for all agents, future data accumulation is necessary.

Table 2. FDA approved targeted therapies for treating childhood cancer or benign hematological diseases and their impact on male fertility.

Molecule	FDA approved indications (paediatric)	Treatment group	Fertility outcome
Imatinib	Ph+ CML in chronic phase and newly diagnosed Ph+ AML	TKIs	Testicular and epididymal weights reduced in male rats exposed at 3/4 of the maximum human clinical dose. Short-term treatment in prepubertal rats does not cause infertility or affect the health of the offspring. In clinical adult human studies: imatinib crosses the blood-testis barrier and decreases sperm count, survival rates, and activity in CML-CP patients. No impact on reproductive organ structure and sex hormone levels. Severe oligozoospermia when imatinib is taken during prepuberty in humans.
Dasatinib	Ph+ CML in chronic phase and newly diagnosed Ph+ AML (age ≥1 y)		No studies on spermatogenesis. In repeated dose studies on rats: reduced size of testis. In clinical adult human studies: 9 reported pregnancies in partners of Dasatinib treated men resulted in birth of normal infants.
Everolimus	Subependymal giant cell astrocytoma with tuberous sclerosis – not candidates for curative surgical resection (age ≥3 y)	mTOR KI	Sperm motility, sperm count, and plasma testosterone levels were diminished in rats treated with at 5 mg/kg. Fertility index increased from 0% to 60% after 12–13 weeks of no treatment.
Gemtuzumab	Newly diagnosed (age ≥1 months) or relapsed/refractory CD33-positive AML (age ≥2 y)	Monoclonal antibody	No studies on spermatogenesis. Decreased fertility index in rats Degeneration of ST and decreased epididymal sperm, not reversable after 6-week drugfree period in monkeys.
Voxelotor	Sickle cell disease (age ≥12 y)	HbS polymerization inhibitor	Sperm motility and morphology decreased in rat models when administered at doses 5 times the human exposure.

Agents that have not been reported to affect spermatogenesis so far are excluded.

AML: acute myeloid leukemia, CML: chronic myeloid leukemia, CML-CP: CML chronic phase, FDA: U.S. Food and Drug Administration, HbS: hemoglobin S, mTOR: mechanistic (mammalian) target of rapamycin, Ph+: Philadelphia chromosome positive, ST: seminiferous tublues, TKI: tyrosine kinase inhibitor.

Data from Wyns et al (Hum Reprod Update 2021;27:433-59) [48].

FERTILITY AFTER CANCER TREATMENT (RECOVERY AND FERTILITY TREATMENT)

The recovery of testicular function after cancer treatment depends on the number of surviving spermatogonia. A treatment with low cytotoxic effect may cause the sperm count to decrease; however, recovery generally occurs at approximately 12 weeks [34]. Conversely, treatments with high cytotoxic effects can cause azoospermia if the spermatogonia do not remain, and even if they do remain, the recovery may take several years. The possibility of recovery decreases, and the period until recovery is delayed if the dose or number of treatment courses is large, even if the same agent/regimen is used throughout. Suzuki et al [50] investigated the time to recovery of spermatogenesis in 45 patients who received antineoplastic agents for testicular cancer (bleomycin, etoposide, cisplatin [BEP] therapy). The authors reported that although 44 patients had recovered, the period until recovery increased with an increase in the number of treatment cycles. Further, no patient in the group that underwent five or more courses recovered spermatogenesis within 2 years [50]. Martinez et al [51] reported that it takes approximately 1 year after adriamycin, bleomycin, vinblastine, dacarbazine (ABVD) therapy and 2 years after cyclophosphamide, hydroxydaunorubicin (adriamycin), oncovin (vincristine), prednisone/mechlorethamine, oncovin (vincristine), procarbazine, prednisone-adriamycin, bleomycin, vinblastin (CHOP/MOPP-ABV) therapy for patients with malignant lymphoma to recover to their pretreatment sperm count levels. Similarly, the sperm count also recovers after radiation therapy at low doses. However, the recovery after 1 Gy of irradiation takes 7 months, whereas the recovery after 6 Gy takes 24 months [34].

After cancer treatment, young male patients are often worried about the recovery of spermatogenesis and the development of chromosomal abnormalities and DNA fragmentation in their sperm. Some patients are concerned that chromosomal and DNA abnormalities may increase the prevalence of malformations in their children. In cases of testicular cancer (BEP therapy), the proportion of sperm with chromosomal aneuploidy increases after two or more treatment courses but normalizes after 24 months [52]. For malignant lymphoma, the proportion of aneuploid spermatozoa detected 3 months after treatment with ABVD therapy and 12 months after treatment with CHOP therapy is higher than the proportion detected before treatment; however, it decreases after the treatment [51]. Thomson et al [53] compared the semen analysis results and SDF rates of male patients who underwent cancer treatment in childhood with those of the participants in a normal control group. Eleven of the 33 cancer survivors had azoospermia only, whereas the remaining patients had decreased sperm count in addition to azoospermia. However, the SDF rate of the patient group was not significantly different from that of the normal control group [53]. Bujan et al [54] also measured pretreatment and post-treatment SDF in patients with testicular cancer who received chemotherapy and radiation therapy. Their results showed that the SDF rate increased 6 months after treatment, but not significantly, and returned to the pretreatment rate in approximately 1 year [54].

Patients and oncologists often have the impression that all patients lose their fertility after cancer treatment. However, the spermatogenesis function of many patients recovers after cancer treatment [55]. Reportedly, 33% of childhood cancer survivors have normal sperm counts and motility [53]. Moreover, 64% of low-stage seminoma (Stages I and IIA) survivors have naturally conceived children [56]. A cohort study of 8,670 male cancer survivors in Denmark and Sweden indicated that 8,162 of the survivors experienced spontaneous pregnancies [57]. Spontaneous pregnancy is possible even in patients who have undergone chemotherapy or radiotherapy. If spermatogenesis cannot be restored, FP may be performed. Currently, the progress of assisted reproductive technology is remarkable, allowing even patients with a low sperm count who did not undergo FP to have children [58]. Even if the patient has azoospermia or an ejaculatory disorder, it is possible to obtain his sperm by performing testicular sperm extraction (TESE) and microsurgical epididymal sperm aspiration [59]. Shin et al [60] reported that they were able to collect sperm from 47% of patients with azoospermia after chemotherapy using micro-TESE. If obstructive azoospermia is present due to cancer surgery or radiation therapy, sperm can be retrieved using conventional TESE or microsurgical epididymal sperm aspiration [30]. There is no difference in clinical pregnancy and live birth rates between cancer survivors and patients who have undergone general infertility treatment [61]. The incidence of congenital malformations in children whose fathers are cancer survivors is slightly higher but not significantly different from that in ordinary children [58,62].

Reassessment of spermatogenesis after treatment is necessary [63]; however, all male cancer survivors require SB after treatment. Communicating this information to patients can alleviate anxiety regarding cancer treatment and fertility prospects largely [58].

FERTILITY PRESERVATION

FP is the only way to prevent infertility caused by cancer treatment. It is important for maintaining the quality of life of patients with cancer after treatment [64]. Considering the fertility crisis caused by cancer treatment, the American Society of Clinical Oncology (ASCO) published guidelines for FP in 2006, which were then updated in 2013 and 2018. These guidelines state that oncologists should discuss SB with postpubertal patients with cancer who received any type of cancer treatment [38,65,66]. The National Comprehensive Cancer Network, like the ASCO, advocates that cancer treatment centers should develop sperm cryopreservation programs for all male patients with cancer [67]. The Japan Society of Clinical Oncology published similar guidelines in 2017. Similar to the other guidelines, the Japanese guidelines recommended that cancer treatment should be prioritized first, and that as patients of a fertile age may become infertile, doctors should inform patients of potential infertility and collaborate with reproductive specialists. Therefore, it is necessary to evaluate the possibility and timing of FP during cancer treatment [68].

There are several ways to preserve the fertility of men. Cryopreservation of sperm or testicular tissues is the most popular method of FP. Shielding the testes to avoid exposure during irradiation is another method. However, shielding the testes against fractionated and scattered radiation has little protective effect [69]. Administration of a gonadotropin-releasing hormone agonist can inhibit the hypothalamic-pituitary-gonadal axis and stop spermatogenesis [70]; however, it has not been proven to be effective in humans [36,71].

The European Society of Human Reproduction and Embryology Task Force designed a cryopreservation algorithm for the preservation of sperm and testicular tissue in prepubertal and adolescent men at risk of losing fertility (Fig. 3) [72]. Sperm cryopreservation is recommended for postpubertal men if they can ejaculate and produce sperm. The European Society for Medical Oncology FP guidelines recommend that semen samples be taken at least three times [73]. The American Society for Reproductive Medicine also recommends taking as many samples as possible [74]. Since cancer treatment deteriorates sperm count and quality, sperm cryopreservation should be performed before the treatment [75]. However, cancer treatment may be prioritized depending on the general condition of the patient. In such cases, a discussion between the oncologist and a reproductive specialist may be required. It is also believed that even if the treatment is initiated before SB, SB should be performed until azoospermia is detected [76]. However, the sperm DNA collected during chemotherapy is more likely to contain gene mutations; therefore, preimplantation genetic testing may be required [77]. Patients with ejaculatory disorders, severe oligospermia, or azoospermia should undergo testicular biopsies to confirm the presence of sperm in the testes. Furthermore, either the mature testis protocol or the immature testis protocol should be selected depending on the presence or absence of sperm in the tissue [72]. Patients who have never masturbated should attempt to undergo a procedure such as vibrostimulation or electroejaculation before proceeding to biopsy [78]. Reportedly, 13.9% to 53.3% of male adolescent patients cannot ejaculate [79,80]; thus, patients and parents must be provided guidance in advance for the treatment to proceed smoothly [81]. The method used for testicular biopsy is similar to that of TESE, which is mainly performed on infertile patients with azoospermia. However, when performed for FP in patients who have insufficient semen for cryopreservation, this testicular biopsy method is called onco-TESE. Although there is no meta-analysis or extensive research on onco-TESE, the sperm retrieval rate is approximately 50% to 60% [82].

Fig. 3. An algorithm developed by Picton et al [72] for cryopreservation of testicular tissue and sperm in prepubertal and pubertal patients, which should be performed prior to high-risk treatments that may lead to infertility. Pubertal patients are first tested for semen and the storage protocol is performed if the semen contains enough storable sperm. Patients unable to produce sperm (including those who cannot ejaculate) or patients with oligozoospermia or azoospermia undergo testicular biopsy (onco-testicular sperm extraction). Intraoperative analysis is performed on the tissues obtained through biopsy. Any sperm cells detected are stored (mature testis protocol). The immature testis protocol is a method of cryopreserving tissues that contain sperm-like cells (spermatogonia to spermatid). Because there is a high probability that there are no sperm cells in the tissue, cryopreservation is employed with the hope that future medical advances will enable differentiation of sperm-like cells (germ cells) into sperm cells. Regarding prepubertal and young pubertal patients, the tissue is collected and cryopreserved on the premise that masturbation is not possible (immature testis protocol). Reproduced from the article of Picton et al (Hum Reprod 2015;30:2463-75) [72] with original copyright holder’s permission.

Sperm may be damaged by cryopreservation. Frozen and thawed sperm have 25% to 75% lower motility [15,83]. Sperm motility after thawing and washing affects the choice of treatment and the success rate of infertility treatment. However, assisted reproductive technology using frozen sperm has a clinical pregnancy rate of approximately 30% and a live birth rate of approximately 25%, which is comparable to the treatment results of general infertility treatment [61,84,85].

Unfortunately, the utilization rate of cryopreserved sperm is not very high. There are few reports of rates that exceed 10% [85]. Although its utilization rate is low, SB exerts a large burden on medical staff and patients, due to factors such as explanation time, high cost, and equipment [86]. Additionally, spermatogenesis in many patients eventually recovers [87], leading to questions regarding the need for SB [88]. However, it is unacceptable to ruin a patient’s future hope regarding SB, as it is not possible to predict accurately whether the patient will present with azoospermia after treatment. Further, if SB can motivate patients to fight cancer, as Saito et al [89] suggested, it should be done.

CRYOPRESERVATION OF TESTICULAR TISSUE AND/OR SPERMATOGONIA FOR PREPUBERTAL BOYS

For prepubertal and early pubertal boys who have not yet produced sperm, testicular biopsy should be performed to cryopreserve their tissue/germ cells from immature testis [72]. Recently, protocols in Europe and the United States have also been created that include FP for boys (Fig. 4) [36]. Spermatogonial stem cells (SSCs) in the testis can be cryopreserved, and future technological progress could permit the differentiation of germ cells into spermatozoa [30,72]. According to studies by Valli-Pulaski et al [90] and Picton et al [72], testicular tissues and spermatogonia have been preserved from approximately 1,000 patients worldwide to date. In general, less than 50% of the testis is excised and cryopreserved. There are almost no complications, and the incidence is around 2% [48].

Fig. 4. Fertility preservation protocol recommended by the Pan Care LIFE 15 Consortium and the International Late Effects of Childhood Cancer Guideline Harmonization Group, including Childhood and AYA generations (CAYA). Green columns are strongly recommended, yellow columns are moderate recommendations, and red columns are not recommended. In children, highly invasive treatments should be avoided as much as possible. Treatment, if any, should be limited to high-risk treatments. CED: cyclophosphamide equivalent dose, HSCT: haematopoietic stem-cell transplantation, TESE: testicular sperm extraction. ^*The total amount of alkylating agent is calculated by CED, and CED of 4,000 mg/m² or more is defined as high-dose, and less than that is defined as low-dose. Reproduced from the article of Mulder et al (Lancet Oncol 2021;22:e57-67) [36] with original copyright holder’s permission.

Since spermatogenesis has not yet occurred in prepubertal boys, spermatozoa are absent from the collected tissue and intraoperative analysis is not performed. A common method is to cryopreserve half of the resected There are three ways to use cryopreserved testicular tissue and SSC after cryopreservation: (1) Testicular tissue transplantation into a host animal [91] or healed host patients. This method has the advantage of being able to grow the patient’s reproductive cells and testicular tissue using the host’s biological environment [48,92]. In non-human primates, studies using other animals as hosts have succeeded in spermatogenesis [93,94]. However, this method has the disadvantages of contamination with cancer cells, the need for surgical procedures to extract sperm, and intracytoplasmic sperm injection to achieve pregnancy [48,92]. In particular, the use of xenograft has risks such as virus infection of animals, so it is difficult to recommend it clinically [48]. (2) In vitro maturation of SSC (organ culture). This is a method of promoting spermatogenesis using somatic tissue (seminiferous tubules) containing SSC. In this method, the spermatogenesis process can be observed, unlike the transplantation of testicular tissue into the host. Also, since the sperm can be collected from the culture, there is no surgical intervention for the patient. This method has been successful in mice, and offspring have also been born from the retrieved sperm [95]. A fairly efficient culture method has also been established [96]. (3) Transplantation of SSC to the testis (seminiferous tubule). The stored SSCs are transplanted into the patient’s seminiferous tubules and colonized. Sperm cells are then produced by natural spermatogenesis [97]. If the differentiation of the transplanted SSC in the testis progresses, spontaneous pregnancy is possible, and the patient does not undergo surgical invasion. It has been successful in animal models [92], but as with the two procedures, there has been no success in humans yet. The main disadvantages include the small number of SSCs that need to be grown when performed on prepubertal boys [92] and the risk of cancer cell contamination. These three preservation methods have been reported to be successful in animal models. However, it is still a treatment with a solid experimental nature, and the burden on prepubertal and early pubertal boys who receive treatment is heavy. Considering the risks and benefits, we believe this should be done only in high-risk boys likely to lose spermatogenesis completely [36,92]. Also, since this article reviews FP in cancer treatment, we will not go into detail about it, but some boys receive FP treatment in addition to those who receive cancer treatment. These include boys undergoing treatment who are likely to develop azoospermia for diseases such as sickle cell, thalassemia, and bone marrow insufficiency and boys who must undergo bilateral orchiectomy [37].

BARRIERS TO FERTILITY PRESERVATION AND POSSIBLE COUNTERMEASURES

The spread of FP is important for the future of cancer survivors. In the United States, 51% of young patients with cancer [6] and 25% of patients with childhood cancer [98] want to become fathers in the future. A Japanese study indicated that one-third of male cancer survivors are worried about fertility, whereas two-thirds of patients who underwent FP said that their attitude toward the treatment was positive [89].

The ASCO guidelines state that “Healthcare providers caring for adult and pediatric patients with cancer should address the possibility of fertility as early as possible before treatment starts” and “Healthcare providers should refer patients who express an interest in FP to reproductive specialists” [38]. However, some oncologists do not know how to perform sperm preservation, and are not familiar with its approximate duration or the burden it will place on the patient [99]. Undoubtedly, it is difficult to explain to the patients about a medical care procedure that they themselves are unaware. Available data indicates that 50% of cancer therapists do not talk to patients about these sequelae [99]. Moreover, several reports indicate that the main barriers to FP include a lack of communication, lack of resources and explanation time, high costs, lack of time to perform FP, and lack of knowledge on the part of doctors [69].

Reproductive medicine specialists expect cancer treatment staff to provide some information to patients regarding sperm preservation prior to FP. In cases where it is difficult to preserve the sperm, close cooperation between the cancer treatment staff and reproductive medicine specialists is required. Further, simple and smooth referrals will benefit both patients and health care professionals. Considering the abovementioned issues, it is necessary for FP facilities and cancer treatment centers to share information and cooperate with each other. In France, there were 23 facilities capable of providing FP services in the country as of 2014; these facilities form an FP utilization network and cover all regions of France [100]. FP facilities are also widely used in the UK [6]. Additionally, 85% of childhood cancer centers are capable of performing pretreatment sperm cryopreservation [101]. On the other hand, in Japan, 91 facilities perform SB as of 2018, and SB is mainly handled by gynecology practitioners (specialists in reproductive medicine). The average number of SBs performed at one facility is 1 to 5 per year because the concentration is not as advanced as at facilities in Europe and the United States [102]. Recently, hospitals and clinics in Japan that provide cancer treatment and reproductive medical care formed a network rapidly in each region (mostly prefectures) to respond to patients who desire FP [103]. Japan’s FP support network provides patients and oncologists with information on cancer and reproductive medicine, disseminates and raises awareness of medical information on regional cancer and reproductive medicine, and promptly collaborates with cancer and reproductive therapists. The Japanese government has introduced a universal health insurance system; however, it does not currently cover FP. Nevertheless, the network and prefectural government have jointly established a subsidy benefit system to reduce the financial burden of FP on patients with cancer.

CONCLUSIONS

Although there are many sequelae of cancer treatment, infertility is a serious problem that threatens the future and life plans of male patients with cancer. Some patients can recover fertility and thus avoid infertility, but unfortunately, some patients cannot have children without reproductive support. By establishing treatments to protect these patients and performing FP as an infertility prevention strategy, they can be treated for cancer without being distressed about infertility. In the future, it is necessary to provide information regarding FP to patients, parents, health care professionals, and oncologists for increasing the awareness of FP. Although there are differences depending on the region and country, infrastructure must be developed so that FP can be performed smoothly. Furthermore, since cancer treatment is generally expensive, FP requires some financial support. Furthermore, there is a need to establish techniques for performing successful extratesticular spermatogenesis in prepubertal patients. Although these procedures are very time-consuming and require patience, they are essential for the preservation of fertility in young male patients with cancer.