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Histologic types of breast carcinoma in relation to international variation and breast cancer risk factors. WHO Collaborative Study of Neoplasia and Steroid Contraceptives.
INTERNATIONAL JOURNAL OF CANCER. 1989 Sep 15; 44(3):399-409.Associations between breast cancer risk factors and histologic types of invasive breast carcinoma were studied in 2728 patients. Lobular and tubular carcinomas occurred with increased relative frequency in most high risk groups. The proportion of these types increased with age to a maximum at 45-49 years and decreased in the following decade. Significantly increased proportions of lobular and tubular carcinomas were also associated with high risk countries, prior benign breast biopsy, bilateral breast cancer, concurrent mammary dysplasia, high age at 1st livebirth, never-pregnant patients compared to those with a 1st livebirth before age 20, private pay status, and length of education. Nonsignificant increases were associated with family history of breast cancer, less than 5 livebirths, less than 25 months total breastfeeding, use of oral contraceptives or IUD, and high occupational class. As a general trend, the higher the overall relative risk, the higher the proportion of lobular and tubular carcinomas. The occurrence of other histologic types also increased breast cancer risk, but to a smaller degree than for lobular/tubular carcinomas. It is suggested that all hormonally related, socioeconomic, and geographic risk factors enter their effect by selectively increasing the number of lobular cells at risk. Family history of breast cancer and age over 49 years did not follow the general trend of parallel increases in the proportion of lobular/tubular carcinomas and breast cancer risk, and may operate through other mechanisms. (author's)