Multi-gene mutation metastatic castrate-resistant prostate cancer

Abstract

Gene panel sequencing of metastatic castrate-resistant prostate cancer (mCRPC) can assist in identifying appropriate targeted therapies. Although some studies have reported single DNA mutations, this is the first case of mCRPC with five different DNA mutations based on gene panel analysis. The patient, a 75-year-old man, initially presented with haematuria. Laboratory investigation revealed elevated prostate-specific antigen levels, and CT showed an enlarged prostate gland with metastatic lymph nodes. A 12-core biopsy revealed adenocarcinoma of the prostate. Gene panel sequencing demonstrated five different DNA mutations associated with sensitivities to olaparib and pembrolizumab. Treatment failure after hormonal therapy with leuprorelin and bicalutamide resulted in the initiation of chemotherapy with docetaxel. Over the past decade, development of genome sequencing analysis may guide us with more precise targeted therapy specific to mCRPC early on, especially with poly (ADP-ribose) polymerase inhibitors may show survival benefits.

Background

Prostate cancer is the most commonly diagnosed non-cutaneous malignancy; an estimated 191 930 men were diagnosed in the USA in 2020 (as reported on Cancer. Net). Prostate cancer is also the most common type of cancer in men and the second-leading cause of cancer-related death in men in the USA,^1–3 and the incidence of metastatic castrate-resistant prostate cancer (mCRPC) is 12.1%. Restoration of androgen activity, reflected by rise in prostate specific antigen (PSA) leads to mRCP with the mean survival of patients with mCRPC is around 1–2 years, and nearly 90% of them develop skeletal metastases, which are associated with almost 100% mortality.

Several studies have identified genomic defects in DNA repair genes in mCRPC, which may be exploited for targeted therapy. One such targeted therapy is poly (adenosine diphosphate (ADP)-ribose) polymerase (PARP) inhibitors, which are DNA-damaging agents that target factors responsible for DNA repair. Approximately 90% of patients with mCRPC have clinically actionable molecular aberrations.⁴ Although germline and somatic DNA mutation analyses can identify mutations that guide therapeutic decision making, such analyses are underused in mCRPC, with only 15% of patients receiving mutational analysis.

Along with antiandrogen therapy, identifying germline and somatic gene mutations that affect cell repair in mCRPC cells, early on block the activity of a protein known as PARP, which helps cells mend specific types of damage to DNA may impact on survival in mCRPC, when tumour burden is low.

To date, studies have identified only one germline or somatic DNA mutation found during sequencing in mCRPC patients. In this case report, we present a 76-year-old man with mCRPC who had five different DNA mutations identified through gene panel testing.

Case presentation

The patient was a 75-year-old man who initially presented to his primary care physician with gross haematuria for a few days. Examination of his complete blood count revealed haemoglobin levels of 8.8 g/dL (normal: 12.0–15.7 g/dL), a white cell count of 7.0×10³/µL (normal: 4.5–11.0×10³/μL), a haematocrit proportion of 27.6% and a platelet count of 181×10³/µL (140–440×10³/μL). The patient had PSA levels of 4 ng/mL. Because of a concern of prostate cancer, a 12-core biopsy was obtained, which indicated adenocarcinoma of the prostate gland with a Gleason score of 4+4. CT of the abdomen showed diffuse wall thickening of the bladder with hyperenhancement and an enlarged prostate gland measuring 6.8×8.7 cm (figure 1). Borderline pelvic and enlarged mesorectal lymph nodes were also observed. CT and bone scans revealed locally advanced cancer with possible metastasis to the lymph nodes. Standard treatment was started with the luteinising hormone-releasing hormone agonist leuprorelin, the nonsteroidal antiandrogen bicalutamide and radiation treatment for metastatic prostate cancer. Gene sequencing showed positivity for a pathogenic variant of ataxia telangiectasia mutated (ATM) kinase, a pathogenic variant of cyclin-dependent kinase 12 (CDK12), mismatch repair status protein deficiency, and microsatellite instability (MSI). The tumour mutational burden (TMB) was high. ATM and CDK12 deficiencies are sensitive to olaparib, and MSI and high TMB are sensitive to pembrolizumab.

Figure 1.

CT of the abdomen showed diffuse wall thickening of the bladder with hyperenhancement and increased size of the prostate gland measuring 6.8×8.7 cm.

Outcome and follow-up

All prostate cancer can be manipulated initially with endrocrine therapy. Identifiable germline mutations in patients with prostate cancer may help us in sequencing of adjuvant therapy in case of mCRPC disease. Our patient failed haromonal treatment, and since the patient had not received any previous chemotherapy, docetaxel therapy was initiated as a next line of therapy. At present, the patients PSA levels continued to decrease to 1.1 ng/mL. He is scheduled to receive proton beam radiation therapy. In the event of failure of therapy or disease progression, as with knowledge of his gene sequencing panel, olaparib and pembrolizumab would be initiated.

Discussion

Understanding the progression of therapy in mCRPC requires insight from the progression of therapy, the mechanism of normal DNA cell repair, identifying germline and somatic gene mutations that affect cell repair in mCRPC cells and progression of disease.

The general therapy for prostate cancer is androgen deprivation therapy, especially for disseminated disease, because the tumour depends on the androgen receptor (AR) for proliferation.⁵ However, over time, tumour progression can lead to androgen deprivation therapy failure and CRP, which generally occurs after 12–24 months. Second-generation AR-directed therapies (abiraterone acetate/prednisone or enzalutamide) are administered if patients fail first-line chemotherapy (docetaxel or cabazitaxel).

mCRPCC has a both germline and somatic gene mutation leading to PSA rise and tumour load with visceral and bone metastasis. According to the National Comprehensive Cancer Network guidelines, genetic germline testing is recommended to identify the germline and somatic mutations in DNA repair genes (table 1).^{6 7}

Table 1.

Germline and Somatic mutations in DNA repair genes

Germline mutations17
Mutation	Extended form
MLH1	MutL homolog1
MSH2	MutS homolog 2
MSH6	MutS homolog 6
PMS2	PMS1 homolog 2
BRCA1	Breast cancer 1
BRCA2	Breast cancer 2
ATM
PALB2	Partner and localiser of BRCA2
FANCA	Fanconi anaemia complementation group A
Somatic gene mutations4
RAD51D	RAD51 paralog
CHEK2	Checkpoint kinase 2
Microsatellite instability
dMMR	Deficient mismatch repair

Although previous studies have shown that 90% of patients with mCRPC have genetic aberrations, they have described only a single mutation in any one patient.⁴ Our study is unique in that we observed five germline DNA mutations based on gene panel sequencing: ATM, CDK12, deficient mismatch repair, MSI and TMB. There have been no other reports of gene panel sequencing with two or more simultaneous gene mutations. There are also no comparison studies of individuals with single or multigene metastatic prostate cancer. Pritchard et al performed a multicentre study to better understand germline mutations in metastatic prostate cancer. We have expanded on their results by including specific germline DNA mutations, as well as the highest number of germline mutations detected in one patient.⁸ The results of these previous studies can be found in the supplemental appendix of Pritchard et al and in table 2.⁹

Table 2.

Comparison of Studies with Germline DNA Mutations vs Our Study

Source of study	Total no of patients	Patients with mutations	Germline DNA mutations	Max no of germline mutations in one patient
Stand Up to Cancer- Prostate Cancer Foundation Discovery Series	150	15 patients (10%)	ATM, BRCA1, BCRA2, RAD51D	1
Stand Up to Cancer- Prostate Foundation Validation Series	84	9 patients (10.7%)	ATM, BRCA1, BRCA2, FAM175A	1
Royal Marsden Hospital	131	16 patients (12.2%)	ATM, BRCA2, CHEK2, MRE11A, MSH6, NBN, PALB2, RAD51C, RAD51D	1
University of Washington	91	8 patients (8.8%)	ATM, BRCA2, CHEK2, GEN1, MSH2	1
Weil Cornell Medical College	69	7 patients (10.1%)	ATM, ATR, BRCA2, CHEK2, RAD51D	1
University of Michigan	43	4 patients (9.3%)	ATM, BRCA1, GEN1, PMS2	1
Memorial Sloan Kettering Cancer Center	124	23 patients (8.5%)	ATM, BRCA1, BRCA2, BRIP1, CHEK2, NBN, PALB2, PMS2	1
Our Study	1	100%	ATM, CDK12, deficient mismatch repair, MSI, TMB	5

ATM, ataxia telangiectasia mutated; BRCA, breast cancer; BRIP1, BRCA1 Interacting Protein 1; CHEK2, checkpoint kinase 2; FAM175A, BRCA1-A complex subunit Abraxas 1; GEN1, Gen, Holliday junction 5’flap endonuclease; MRE11A,; MSH6, MutS homolog; MSI, microsatellite instability; NBN, Nibrin; PALB2, partner and localiser of BRCA2; PMS2, PMS1 homolog 2; RAD51, RAD51 paralog; TMB, tumour mutation burden.

Several studies have assessed the role of next-generation sequencing in studying mCRPC and its potential for improving patient care. The Stand Up To Cancer-Prostate Cancer Foundation International Dream Team pursued whole-exome and transcriptome sequencing of 150 mCRPC biopsies. CDK12 had a mutation frequency of 4.7%, MLH1 a mutation frequency of 1.3%, MSH2 a mutation frequency of 3.0%, and ATM a mutation frequency of 7.3%.⁶ Applying these frequencies to our study would provide a 1 in 100 000 chance of detecting all these mutations in the same patient at the same time. No previous study has found more than one germline mutation in one patient at a time. Our results, like those of previous studies, shows the necessity of sequencing for germline and somatic DNA mutations. This information may help guide the diagnosis and management of mCRPC.^{6 7 9} With the limited amount of studies, further research and trials need to be undertaken to clinically qualify the rarer genomic mutations.

Second-line hormonal treatments, such as abiraterone and enzalutamide, have been used in mCRPC after chemotherapy failure. Alternating between chemotherapy and antihormonal therapy has also shown some promising effects. When these therapies do not work, PARP inhibitors should be considered.^{10 11} The mechanism of action includes inhibition of repair of DNA single-strand and double-strand breaks in cancer cells.^{2 5 12} The most commonly administered PARP inhibitor is olaparib.⁶ Studies have shown longer progression-free survival and better overall response with olaparib compared with enzalutamide or abiraterone.¹³ The effects of this drug have been studied in breast cancer (BRCA1) and BRCA2 mutation carriers and patients with other germline mutations.^{6 14} Other PARP inhibitors include rucaparib, veliparib, niraparib and talazoparib. The side effects of PARP inhibitors include anaemia, thrombocytopaenia, fatigue and gastrointestinal toxicities.⁶ Because of the high frequency of gene mutation in highly aggressive disease compared with localised prostate cancer or normal tissues, these drugs are particularly useful in mCRPC.¹⁵

PD-L1 inhibitors have also been recently approved for later line treatments if PD-L1 expression is high and the patient has MSI.¹⁵ PD-L1 is a ligand that binds to the PD-1 receptor on T cells and has the ability to reduce the production of T-cells and cytokine release. PD-1 inhibitors block its interaction with PD-L1, which can help to restore T-cell function.¹⁶

In conclusion, we present a rare case of mCRPC with five DNA mutations based on gene panel testing. Many of these individuals become castrated because they fail androgen deprivation therapy. A biopsy is used for diagnosis along with CT imaging to help guide the diagnosis of metastatic lesions. Identifying gene mutations can help guide therapy, as PARP inhibitors will prevent the repair of SSBs and DSBs to ensure the death of cancer cells. First-line therapies include chemotherapeutic options including docetaxel, and second-line hormonal therapies including enzalutamide or abiraterone. Gene panel testing will allow for further treatment planning, if previous treatments fail or have disease progression. With further research, if gene panel testing becomes more efficacious, then may also be possible to apply to earlier prostate cancer disease stages.¹²

Patient’s perspective.

I didn’t think that this journey would end up like this and I didn’t think they would spread. I couldn’t believe that my bloody urine caused all of this. I am definitely thankful to everyone who supported me and I was shocked to hear that there were five different mutations do to my tumortumour. I want other people to learn from me because I have a unique kind of cancer. When I heard about hte proton beam therapy, I felt that in addition to chemotherapy, that it will help. I will always continue to fight against my prostate cancer.

Learning points.

• Patients with metastatic castrate-resistant prostate cancer should undergo germline and somatic DNA mutation analyses to identify therapies specific for these mutations.

• Gene panel testing will allow for further treatment planning, if previous treatments fail or have disease progression.

• First-line chemotherapy for prostate cancer includes docetaxel and second-line hormonal therapy includes enzalutamide or abiraterone.

• Olaparib and other polymerase inhibitors repair both single-and double-strand breaks in tumours with DNA repair deficiency.

Ethics statements

Patient consent for publication

Obtained.