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TestisLinda Morris Brown, M.P.H.*
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The testes are the paired male reproductive glands that produce the hormone testosterone and, after sexual maturity, spermatozoa (sperm). The testes form in the abdominal cavity early in fetal development and usually descend into the scrotum before birth. Almost all testicular cancers are germ cell tumors. There are two major histological groupings of testicular cancer: seminoma and nonseminoma. Seminomas are more common in men 35 and older, while nonseminomas are more common in younger men 15-24 (Brown et al., 1986a).
Testicular cancer is rare in the United States, accounting for only 1 percent of cancers in males. It is, however, the most common malignancy among white males aged 20 to 34 and the second most common among white males aged 15 to 19 and 35 to 39. The incidence rate for white males (5.1 per 100,000) is over six times that for black males (0.8 per 100,000) (Ries et al., 1994). In the United States, the incidence rates of testicular cancer among Hispanics, Native Americans, and Asians are less than those for whites, but greater than those for blacks (Muir et al., 1987). Men in Scandinavian countries have the highest incidence of testicular cancer in the world--a rate 45 percent greater than that for white men in the United States (Parkin et al., 1992). Mortality from testicular cancer is low in both white (0.3 per 100,000) and black (0.1 per 100,000) U.S. males (Ries et al., 1994). Because of advances in treatment, survival was 94 percent in 1983-90, up from 79 percent in 1974-76. The incidence of testicular cancer has doubled in the past two decades, with the most striking increases occurring among young men 15-44. Undescended testis, inguinal hernia, testicular trauma, mumps orchitis, elevated testicular temperature, vasectomy, electromagnetic fields (EMF), and hormonal, prenatal, and occupational factors have been implicated in the development of testicular cancer in young adults. Individuals with cryptorchidism or undescended testis are at an increased risk for developing testicular cancer, with approximately 10 percent of testicular cancer patients reporting a history of this condition. Risks of testicular cancer associated with undescended testes have ranged from 2.5 to 17.1 (Brown et al., 1987), with the excess risk in cryptorchid men decreasing with increasingly early age at correction (Pottern et al., 1985; Strader et al., 1988a). Inconsistent findings regarding the degree and significance of the risk of testicular cancer associated with inguinal (groin) hernia have been reported (Coldman et al., 1982; Pottern et al., 1985; Swerdlow et al., 1987a). Significantly elevated risks have been suggested for other antecedent conditions including hydrocele, atrophic testis, and supernumerary nipples (polythelia) (Goedert et al., 1984; Swerdlow et al., 1987a; Haughey et al., 1989; Brown et al., 1987). Also, a higher rate of cryptorchidism, inguinal hernia, and hydrocele was reported in families prone to testicular cancer, suggesting a relationship between urogenital maldevelopment and predisposition to testicular cancer (Tollerud et al., 1985). An association between testicular trauma and testicular cancer has been suggested (Brown et al., 1987; Coldman et al., 1982); however, another study (Swerdlow et al., 1988a) found no association with traumas commonly encountered in everyday life. Although a recent study in upstate New York (Haughey et al., 1989) reported elevated risks for men who preferred baths to showers and who reported having a disease associated with a high fever, three other case-control studies found no excess risk associated with elevation of testicular temperature by external means (Brown et al., 1987; Swerdlow et al, 1988a; Karagas et al., 1989). Two suggested risk factors, vasectomy and EMF exposure from the use of electric blankets, have not been found to be significant risk factors for testicular cancer (Brown et al., 1987; Strader et al., 1988a; Verreault et al., 1990). Maternal factors including nausea of pregnancy severe enough to require treatment, unusual bleeding or spotting during pregnancy, as well as low birth weight and early birth order have been associated with excess risk of testicular cancer (Depue et al., 1983; Brown et al., 1986b; Swerdlow et al., 1987b; Gershman et al., 1988) and suggest that raised maternal levels of available estrogen early in pregnancy may be related to development of testicular cancer in the son. Although in utero DES exposure has been linked to vaginal cancer in daughters and to testicular abnormalities in sons of women who took it to prevent miscarriages (DES Task Force, 1981), prenatal DES exposure has not been linked to testicular cancer (Brown et al., 1986b; Moss et al., 1986; Gershman et al., 1988). An association between employment in professional occupations and the risk of testicular cancer has been reported in several case-control studies (Graham et al., 1977; Ross et al., 1979; Swerdlow et al., 1988b). Farming has been associated with excess risk of testicular cancer in some studies (Mills et al., 1984; Wiklund et al., 1986), but not in others (Brown and Pottern, 1984; Jensen et al., 1984; Sewell et al., 1986). A recent case-control study found a significant increase in risk for exposure to fertilizers (Haughey et al., 1989). The dramatic increase in testicular cancer incidence over time for young men suggest that an environmental factor, with a similar variation over time, might be responsible. Given the magnitude of this increase, one would expect that this factor should have been identified by analytical epidemiological studies. However, to date the factors responsible for these dramatic increases remain elusive. The increases do not appear to be related to improved diagnostic practices nor to any of the risk factors identified to date in case-control studies. |
* From the Biostatistics Branch, Division of Cancer Etiology, National Cancer Institute, Bethesda, Maryland
