Rune Jacobsen, Erik Bostofte, Gerda Engholm, Johnni Hansen, Jørgen H. Olsen, Niels E. Skakkebæk, Henrik Møller.
 

Centre for Research in Health & Social Statistics

The Danish National Research Foundation, Copenhagen

Rune Jacobsen, researcher

Gerda Engholm, senior researcher

The Sperm Analysis Laboratory, Copenhagen

Erik Bostofte, consultant

Institute of Cancer Epidemiology,

The Danish Cancer Society, Copenhagen

Johnni Hansen, researcher

Jørgen H. Olsen, head of department

Department of Growth and Reproduction,

National University Hospital, Copenhagen

Niels E. Skakkebæk, professor

Thames Cancer Registry,

Guy’s, King’s and St Thomas’ School of Medicine, London

Henrik Møller, professor
 

Correspondence to:

Rune Jacobsen,

Centre for Research in Health & Social Statistics

The Danish National Research Foundation,

Sejrøgade 11,

DK-2100, Copenhagen

Email: cerefo@inet.uni2.dk
 
 
 

Abstract

Objective To explore the associations between semen characteristics and subsequent risk of testicular cancer.

Design Cohort study.

Study subjects Men who had a semen analysis done at the Sperm Analysis Laboratory in Copenhagen in the period 1963-1995 (n=32442). As the basis for comparison for testicular cancer incidence served the total population of Danish men.

Outcome measures Standardised morbidity ratios.

Results Males of couples with fertility problems were more likely to develop testicular cancer than other men (89 cases; standardised morbidity ratio=1.6; 95% confidence interval: 1.3-1.9). The risk was relatively constant over time from semen analysis to testicular cancer diagnosis. Analysis according to specific semen characteristics showed that low semen concentration (standardised morbidity ratio: 2.3), poor motility of the spermatozoa (standardised morbidity ratio: 2.5) and high proportion of morphologically abnormal spermatozoa (standardised morbidity ratio: 3.0), were all associated with an increased risk of testicular cancer. The only other cancer site that showed increased incidence was "peritoneum and other digestive organs" (6 cases; standardised morbidity ratio: 3.7; 95% confidence interval: 1.3-8.0). Of these, two cases were probably and two cases were possibly extra-gonadal germ cell tumours.

Conclusion The results point towards the existence of common aetiological factors for low semen quality and testicular cancer. Low semen quality may also be associated with increased incidence of extragonadal germ cell tumours.

Introduction

The possible decrease in semen quality ^{1, 2}, and the increase in testicular cancer incidence in many populations, ^{3, 4, 5} lead to the question whether these temporal trends are independent phenomena or, alternatively, somehow connected to each other. ^{6, 7, 8} Case-control studies on subfertility and subsequent risk of testicular cancer have shown conflicting results. ^{8, 9} However, a recent Danish population based cohort study also found an increased risk of testicular cancer in men with few children for their age, ¹⁰ thus supporting the earlier Danish case-control study ⁸. In both of the Danish studies on subfertility as a risk factor for testicular cancer, the used measure of fertility was the number of children fathered at a given age. Hereby, some men with normal reproductive potential will inevitably be classified as having low relative fertility, because they have no or few children for reasons unrelated to their ability to reproduce. A more direct measure of subfertility is provided by semen analysis where fertility is characterised by various semen measures, e.g. spermatocyte concentration, motility and morphology. ^{11, 12} It has been shown that men with testicular cancer often have abnormal semen characteristics, ^{13, 14} but no study has investigated the association between abnormal semen quality and testicular cancer in a prospective design. In the present paper we explore the incidence of testicular cancer in relation to semen characteristics in 32442 men who had semen analysis done at the Sperm Analysis Laboratory in Copenhagen in the period 1963-1995.
 

Materials and methods

Information on males of couples with fertility problems who had a semen analysis done at the Sperm Analysis Laboratory in Copenhagen in the period 1963-1995 (n=32442) was linked with the Danish Cancer Registry, which holds information on all cases of cancer in the Danish population from 1943 to 1995. ¹⁵ Men who visited the laboratory for other reasons (e.g. semen analysis following vasectomy) were excluded from the analysis. Men with previous cancer to semen analysis were excluded. For men who had multiple semen tests only their first test was used in the analysis. Similarly, only the first cancer diagnosis in a given man was included in the analysis. For each man information on date of birth, dates of birth of their children and date of death were obtained from the Central Population Register and from the National Death Register. Following these linkages, information was available for each man on date of birth, birth dates of children, date of first semen analysis, sperm concentration (million/ml), sperm motility (poor, good), morphologically abnormal spermatozoa (%), date of cancer diagnosis, cancer diagnosis, and date of death. The methods used for the semen analysis have been described. ¹⁶

Expected numbers of cancer cases in the cohort as estimated by multiplying years at risk with primary cancer rates in the Danish population, and standardised morbidity ratios and 95% confidence intervals were calculated using a Fortran computer program. ¹⁷ The standardised morbidity ratios were calculated for each type of cancer by time since first semen analysis and by stratification of the semen characteristics according to standard definitions of subfertility. ¹² The group of azoospermic men was divided into those with previous born children and those without children, in order to address the possibility that some azoospermic men had not given information on sterilisation or other circumstances resulting in a sudden azoospermia. To examine the separate and joint effects of the three semen characteristics, the cohort was stratified into groups according to their combination of semen measures.
 

Results

Overall, the cohort members had an increased risk of testicular cancer and of cancers in the group "peritoneum and other digestive organs" (Table 1). No increased risk for other specific types of cancer was observed in the cohort. For testicular cancer there were 89 cases, giving a standardised morbidity ratio of 1.6 (95% confidence interval: 1.3-1.9). Of the 89 cases of testicular cancers, 50 were seminomas, 37 were non-seminomas and 2 were unspecified. For "peritoneum and other digestive organs" the standardised morbidity ratio was 3.7 (95% confidence interval: 1.3 - 8.0), based on 6 observed cases. The standardised morbidity ratio for cancers of all other sites combined was 1.0 (95% confidence interval: 0.9 - 1.1).

The standardised morbidity ratios for testicular cancer stratified by time since first semen analysis until testicular cancer diagnosis are shown in Table 2. The highest risk of testicular cancer was found within the first 2 full years following the first semen analysis (standardised morbidity ratio=1.8) and remained relatively constant afterwards. The trend in the standardised morbidity ratios over the four periods of follow-up was not statistically significant (P=0.46).

The standardised morbidity ratios of testicular cancer, stratified by semen quality measures, are shown in Table 3. In univariate analyses, low semen concentration, poor semen mobility and a high proportion of abnormal spermatozoa, were all associated with increased standardised morbidity ratios, whereas the not subfertile groups had standardised morbidity ratios closer to unity. The group of azoospermic men who had fathered children before semen analysis showed lower risk of testicular cancer than azoospermic men without children (standardised morbidity ratio: 2.0 vs. 3.5). Men who were not azoospermic but who had sperm concentrations below 20 mill spermatozoa/ml had a higher risk of testicular cancer than men with more than 20 mill/ml (standardised morbidity ratio: 2.3 vs. 1.1).

The univariate, separate and joint effects of the three semen quality measures were analysed in the subgroup of 29177 men who had some spermatozoa in the semen sample (Table 4). The separate effect of low concentration on the risk of testicular cancer was approximately the same as the univariate effect (standardised morbidity ratio: 2.1 and 2.3, respectively). Out of 10509 men with low semen concentration, 9187 had low concentration as the only abnormal characteristic. Very few men had poor motility only or a high proportion of abnormal spermatozoa only, and no case of testicular cancer was observed in these groups. It was therefore not possible to identify a separate effect of poor motility or of having a high proportion of abnormal spermatozoa. However, the risk of testicular cancer increased with increasing number of sub-fertility measures present. The standardised morbidity ratio was 1.9 for one sub-fertility measure, 2.7 for two measures and 9.3 for all three sub-fertility measures.

The details on the six cases of cancer in "peritoneum and other digestive organs" are shown in Table 5. Case 1 may have had a testicular cancer prior to his leukemia, and an extragonadal germ cell tumour is also possible for Case 2 who had increased tumour markers. The notifications suggest that Cases 3 and 5 had extragonadal germ cell tumors. Case 4 and 6 seemed unlikely to have extragonadal germ cell cancers.

Discussion

The present retrospective cohort study, based on more than 30,000 males of infertile couples, showed a strong association between subfertility and subsequent risk of testicular cancer. All men of couples with fertility problems were 1.6 times more likely to develop testicular cancer than the Danish male population in general. The overall analysis included some fully fertile men from couples where only the woman was subfertile, and the observed higher risk of testicular cancer in the cohort overall would be even higher if only men from couples with a male problem were included. Men in the cohort with semen characteristics classified as subfertile, had 2-3 fold increased risk compared to the population risk.

No epidemiological investigation has been conducted previously on specific sperm characteristics and subsequent risk of testicular cancer. However, investigations on spermatogenesis in patients with unilateral testicular cancer¹⁸ and on risk of testicular cancer in men considered subfertile due to a low number of children for their age^{8, 10} are consistent with these findings.

The observation of impaired spermatogenesis in patients with unilateral testicular cancer ¹⁸ does not preclude the possibility that impaired reproductive capacity is secondary to the cancer. In the present study, the risk of testicular cancer was relatively constant over time since semen analysis. This indicates that the state of impaired spermatogenesis was present many years before the diagnosis of testicular cancer, pointing towards a permanent state of impaired spermatogenesis.

The use of semen characteristics as the subfertility measure in the present study eliminates the misclassification problems in studies based on numbers of children, where men with normal reproductive potential having no or few children for other reasons than their ability to reproduce, and where adoptions may influence the results.

All together, the available data points towards the existence of a common risk factor for impaired spermatogenesis and testicular cancer. Some indications exist for a prenatal offset of testicular cancer. A lower incidence of testicular cancer among men born during the second world war than men born before and after the war has been found in Denmark, Norway and Sweden. ^{19, 20, 21} Other risk factors for testicular cancer, such as low birth weight²² and congenital malformations of the male genital organs, ^23,24 further indicates that testicular cancer has its origin in foetal life. A biological indication for foetal origin of testicular cancer is that carcinoma in situ (the precursor of both seminomas and non-seminomas) has several characteristics in common with foetal germ cells.²⁵ The specific aetiological factors in testicular cancer are unknown, but maternal oestrogens and hormonal disrupting agents have been proposed as causal possible factors acting on the male foetus.^26,27

In the present study, an increased risk was also found for cancer in "peritoneum and other digestive organs". A possible explanation for this association could be that some of the observed cancers in this category were misclassified testicular or extragonadal germ cell tumors. Extragonadal germ cell tumours have been associated with testicular carcinoma in situ, ^{28, 29} suggesting a common aetiology with testicular cancer. Alternatively, the extragonadal tumour may be of metastatic origin, as has been suggested by the observation of a ‘scar’ possibly arising from ‘burned out’ testicular cancer. From the review of notification forms in the Danish Cancer Registry, we noticed some erroneous registrations. Pending further pathological review of these tumours, we conclude that the apparent excess of extragonadal germ cell tumours may, in part, be due to misclassified testicular cancers.
 

Contributors: RJ was responsible for the study design, data collection, statistical analysis, interpretation and reporting, and is the guarantor. EB, GE, JH, JHO, NES and HM contributed to the study design, data collection, interpretation and reporting.

The study was funded by the Danish Research Councils.

Competing interests: None declared.
 

Key Messages

• The incidence of testicular cancer has increased in the past 50 years, and some evidence suggests that sperm quality has decreased in the same period
• It has been hypothesised that common aetiological factors may exist for testicular cancer and male subfertility
• The association between testicular cancer and low semen quality is strong and consistent with the hypothesis of a common aetiology
• Subfertility may also be associated with extragonadal germ cell tumours

References

1. Carlsen E, Giwercman A, Keiding N, Skakkebæk NE. Evidence for decreasing quality of semen during past 50 years. BMJ 1992;305:609-13.

2. Swan SH, Elkin EP, Fenster L. Have sperm densities declined? A reanalysis of global trend data. Environ Health Perspect 1997;105:1228-32.

3. Coleman MP, Esteve J, Damiecki P, Arslan A, Renard H. Trends in cancer incidence and mortality. IARC Sci Publ 1993;121:1-806.

4. Forman D, Møller H. Testicular cancer. Cancer Surv 1994;19-20:323-41.

5. Adami HO, Bergström R, Mohner M, Zatonski W, Storm H, Ekbom A, Tretli S, Teppo L, Ziegler, Rahu M, et al. Testicular cancer in nine northern European countries. Int J Cancer 1994;59:33-8.

6. James WH. Secular trends in monitors of reproductive hazard. Hum Reprod 1997;12:417-21.

7. Møller H. Trends in sex-ratio, testicular cancer and male reproductive hazards: Are they connected? APMIS 1998;106:232-39.

8. Møller H, Skakkebæk NE. Risk of testicular cancer in subfertile men: Case-control study. BMJ 1999;318:559-62.

9. Swerdlow AJ, Huttly SR, Smith PG. Testis cancer: post-natal hormonal factors, sexual behaviour and fertility. Int J Cancer 1989;43:549-53.

10. Jacobsen R, Antoniades B, Bostofte E, Engholm G, Hansen J, Skakkebæk NE, Møller H.

Fertility and offspring sex ratio of men who develop testicular cancer: cohort study, submitted

to Human Reproduction in December, 2000

11. Bostofte E, Serup J, Rebbe H, Interrelations among the characteritics of human semen, and a new system for classification of male infertility. Fertil Steril 1989;41:95-102.

12. WHO Laboratory Manual for Examination of Human Semen and Sperm-cervical Mucus Interaction, Cambridge University Press, 1999.

13. Nijman JM, Schraffordt Koops H, Kremer J, Willemse PHB, Sleijfer DT, Oldhoff J. Fertility and hormonal function in patients with nonseminomatous tumor of of the testis. Archives of Andrology 1985;14:239-46.

14. Carroll P, Whitmore WF Jr, Herr HW, Morse MJ, Sogani PC, Bajorunas D, Fair WR, Chaganti RSK. Endocrine and exocrine profiles of men with testicular tumors before orchidectomy. J Urol 1987;137:420-23

15. Storm HH. The Danish Cancer Registry, a self-reporting national cancer registration system with elements of active data collection. IARC Sci Publ 1991;95:220-36.

16. Bostofte E, Bagger P, Michael A, Stakemann G. Fertility prognosis for infertile men: results of follow-up study of semen analysis in infertile men from two different populations evaluated by the Cox regression model. Fertility and sterility 1990;54:1100-06.

17. Coleman M, Douglas A, Hermon C, Peto J, Cohort study analysis with a Fortran computer program. Int J Epidemiol 1986; 15: 134-7.

18. Berthelsen JG, Skakkebæk NE. Gonadal function in men with testis cancer. Fertil Steril 1983;39:68-75.

19. Møller H. Clues to the aetiology of testicular germ cell tumours from descriptive epidemiology. Eur Urol 1993;23:8-13.

20. Bergström R, Adami HO, Mohner M, Zatonski W, Storm H, Ekbom A, Tretli S, Teppo L, Akre O, Hakulinen T. Increase in testicular cancer incidence in six European countries: a birth cohort phenomenon. J Natl Cancer Inst 1996;88:727-33.

21. Wanderås EH, Grotmol T, Fossa SD, Tretli S. Maternal health and pre- and perinatal characteristics in the etiology of testicular cancer: a prospective population- and register-based study on Norwegian males born between 1967 and 1995. Cancer Causes Control 1998;9:475-86.

22. Møller H, Skakkebæk NE. Testicular cancer and cryptorchidism in relation to prenatal factors: case-control studies in Denmark. Cancer Causes Control 1997;8:904-12.

23. United Kingdom Testicular Cancer Study Group. Aetiology of testicular cancer: association with congenital abnormalities, age at puberty, infertility, and exercise. BMJ 1994;308:1393-9.

24. Møller H, Prener A, Skakkebæk NE. Testicular cancer, cryptorchidism, inguinal hernia, testicular atrophy, and genital malformations: Case control studies in Denmark. Cancer Causes Control 1995;7:264-74.

25. Skakkebæk NE, Berthelsen JG, Giwercman A, Müller J. Carcinoma-in-situ of the testis: possible origin from gonocytes and precursor of all types of germ cell tumors except spermacytoma. International Journal of andrology 1987;10:19-28.

26. Sharpe RM, Skakkebaek NE. Are oestrogens involved in falling sperm counts and disorders of the male reproductive tract? Lancet 1993;341:1392-5.

27. Henderson BE, Benton B, Jing J, Yu MC, Pike MC, Risk factors for cancer of the testis in young men, Int J Cancer 1979 May 15;23(5):598-602

28. Daugaard G, Rorth M, von der Maase H, Skakkebaek NE Management of extragonadal germ-cell tumors and the significance of bilateral testicular biopsies. Ann Oncol 1992 Apr;3(4):283-9

29. Daugaard G, von der Maase H, Olsen J, Rorth M, Skakkebaek NE, Carcinoma-in-situ testis in patients with assumed extragonadal germ-cell tumours. Lancet 1987 Sep 5;2(8558):528-30
 
 

Table 1. Standardised morbidity ratios and 95% confidence intervals for different cancers in a cohort of 32442 men attending the Sperm Analysis Laboratory in Copenhagen in the period 1963-1995
 

*p<0.05

Table 2. Standardised morbidity ratios and 95% confidence intervals for testicular cancer, stratified by time since semen analysis.
 

*p<0.05

Table 3. Standardised morbidity ratios and 95% confidence intervals for testicular cancer for different semen characteristics.
 

* p<0.05, ¹ Excluding 2675 azoospermic men.

Table 4. Separate and joint effects among three semen quality measures and risk of testicular cancer among 29177 men with some spermatozoa present in their semen sample.
 

^{* p<0.05, 1 Excluding 2675 azoospermic men.}

Table 5. Evaluation of the six cases of "peritoneum and other digestive organs" based on notification forms and the cancer registry