Sexual, reproductive and contraceptive risk factors were investigated in a matched community-based case-control study of carcinoma-in-situ of the uterine cervix in Sydney. The risk was related strongly to the number of sexual partners: women who had had seven or more sexual partners in a lifetime had a six-fold increased risk compared with those with one or no partner. Early age at first sexual intercourse was also a risk factor, but this effect was reduced substantially after adjustment for the number of partners, with only a two-fold excess risk persisting for those with first intercourse before the age of 16 years as compared with those whose first sexual intercourse was at the age of 25 years or later. The long-term use of oral contraceptive agents was associated with an elevated risk (relative risk, 2.3 for more than six years of use); this effect was maintained for both oestrogen and progestogen doses. The risk increased with the number of induced abortions that had been undergone (relative risk, 2.2 for two or more abortions), but this effect was not statistically significant. A protective effect was found for women who had had a tubal ligation, for those who practised the rhythm method of birth control, and for women who breastfed. It is possible that these reduced risks may relate to unmeasured variables of life-style.
PIP: The extent to which sexual, reproductive, and contraceptive factors are associated with an increased risk of in situ cervical cancer was investigated in 117 Australian women with newly diagnosed cervical intraepithelial neoplasia type 3 and 196 matched controls. The risk of carcinoma in situ of the uterine cervix was found to increase from 4.5 for women with 2-3 sexual partners to 8.1 for those with 7 or more partners when compared to the risk for women with 1 or 0 partners. When these effects were adjusted for the other known risk factors of carcinoma in situ--age at 1st sexual intercourse, the duration of oral contraceptive (OC) use, and smoking--women who reported 2-3 sexual partners had an adjusted risk of 3.2, those with 4-6 partners had an adjusted relative risk of 4.2, and those with 7 or more had an adjusted risk of 6.3 compared to women with 1 or 0 partners. The effect of early age at 1st intercourse on the risk of carcinoma in situ was reduced substantially after adjustment for the number of sexual partners, with only a 2-fold excess risk persisting for those with 1st intercourse before the age of 16 years compared with those whose 1st intercourse occurred at 25 years of age or later. Longterm OC users were also found to be at increased risk of carcinoma in situ. Women with more than 6 years of OC use had an adjusted relative risk of 2.3 compared with never users. There were also increasing risks with increasing lifetime dosages of estrogen and progestogen. Risk increased to 2.2 for women who had undergone 2 or more abortions compared with women who had never had an abortion, but this effect was not statistically significant. Finally, a protective effect against carcinoma in situ of the uterine cervix was found among women who had undergone tubal ligation, those who utilized the rhythm method of fertility control, and women who breastfed; however, these reduced risks may be related to unmeasured life-style variables. No relationship was noted between the risk of carcinoma in situ and age at menarche, number of pregnancies, the age at 1st live birth, or the age at 1st breastfeeding.