COMMENTS

The epidemiology of testicular germ cell cancer is relatively well understood, but less is known about the epidemiology of ovarian germ cell cancer. Cases of testicular (7910) and ovarian (453) germ cell cancer diagnosed 1960-1999 were extracted from the Thames Cancer Registry. The incidence rate in males doubled in the period from 2.0 to 4.4 per 100,000. In females the rate was much lower but the rate of increase over the period was similar to the increase in males. In both sexes the incidence increased sharply around the age of onset of puberty and decreased in older age groups. The biological mechanism of initiation of germ cell carcinogenesis is similar in males and females and probably occurs with roughly the same frequency in the two sexes. In males, the initiated cell population is promoted by the normal action of adult sex hormones to form carcinoma in situ, consisting of many millions of cells. The incidence of testicular cancer is rate limited by the development of carcinoma in situ. The key difference between males and females, which may explain the different levels of incidence, is the much lower number of susceptible cells in females at the time of puberty.