AGE AT FIRST FULL-TERM PREGNANCY, LACTATION AND PARITY AND RISK OF BREAST-CANCER - A CASE-CONTROL STUDY IN SPAIN

A case-control study was carried out in Spain to assess associations b etween parity, lactation and age at first full-term pregnancy and brea st cancer. From November 1989 to February 1992, 184 incident breast ca ncer histologically confirmed cases were interviewed and matched by ag e. and residence to 184 hospitalized patients and 184 community contro ls selected by random digit dialing. Multiple logistic regression was used to assess the independent influence of each factor on the risk of breast cancer in relation to other factors included in the model. Age at first full-term pregnancy was associated with breast cancer risk w ith an estimated odds ratio of 3.5 (95% CI 1.41-9.83) for women with t heir first birth after 30 years in comparison with those whose first b irth was before age 21. Breast cancer risk decreased with increasing n umber of full-term pregnancies, OR 0.3 (95% CI 0.16-0.78) for women wh o had had more than 3 full-term pregnancies in comparison with nullipa rous women, Among parous women, the estimated OR for women with more t han 3 children was 0.4 (95% CI 0.13-0.81) after allowance for age at f irst childbirth and lactation. The estimated OR was 2.6 (95% CI 1.4-4. 7) for women with a positive history of breast cancer in first-degree relatives. Breast cancer was not associated with total duration of lac tation. The study indicates that parity is an independent risk factor associated to breast cancer and that the women with a late age at firs t full-term pregnancy constitute a high-risk group.