Parity and cancer risk in Slovakia.

Mortality data from women aged 45-74 who died between 1968 and 1977 in Slovakia, Czechoslovakia, were used to examine the effect of parity (number of live-born children) on risk of dying from each of 20 common cancers. After controlling for the effects of age and year of death, the effect of parity on risk was statistically significant at the p less than 0.001 level, for cancers of the stomach, liver, gall-bladder, breast, cervix, and ovary; and at the p less than 0.01 level for uterine corpus and brain. No effect of parity was seen for cancer of the colon or rectum. Among parous women the trend relating risk to level of parity was significant at the p less than 0.001 level for cancers of the breast, uterine corpus, ovary and brain; and at the p less than 0.01 level for stomach cancer. The findings relating parity to cancers of the breast and reproductive organs are consistent with previous reports. The associations of parity with cancers of the digestive tract deserve further study.