SEX-DIFFERENCES IN TIME TRENDS OF COLORECTAL-CANCER IN ENGLAND AND WALES - THE POSSIBLE EFFECT OF FEMALE HORMONAL FACTORS

Differences between the sexes in time trends of colorectal cancer inci dence 1962-87 and mortality 1960-91 in England and Wales are examined in relation to changes in female hormonal factors. There was a trend i n the sex ratio of this tumour, particularly marked for the descending colon, whereby the female excess in risk at young ages has almost dis appeared but the male excess al older ages has increased. This trend s tarted for cohorts born since the 1920s and coincided with I-he increa se in the use of oral contraceptives and, to a lesser extent, with inc reases in fertility. The decline has been particularly pronounced for women at young ages born since 1935-39, coinciding with the spread of oral contraceptive use to younger age groups. These results are consis tent with the hypothesis that female hormonal factors may play a role in the aetiology of colorectal cancer and with the possibility that or al contraceptive use might exert a protective effect in the descending colon.