Risk factors for fibroadenoma: a case-control study in Australia.

Risk factors for fibroadenoma were examined in a case-control study involving 117 fibroadenoma cases ascertained by a major private pathology laboratory in Adelaide, Australia, between January 1983 and October 1985. For each case a population control was randomly selected from the electoral roll in Adelaide and matched to the corresponding case by sex, age, and socioeconomic grading of area of residence. Another 189 women whose first biopsy for benign breast disease was examined in the same laboratory during the same time period as those of the cases, but did not show evidence of epithelial proliferation, were also included in the study as a biopsy control group. Risk of fibroadenoma was associated inversely with the Quetelet index, but there was no evidence of an association with age at menarche or menopausal status. The risk of fibroadenoma decreased with an increasing number of full-term pregnancies and was increased in association with use of oral contraceptives at an early age (under 20 years); however, these two associations were observed only when cases were compared with the population controls. Alcohol consumption and dietary fat intake were found not to be associated with altered risk of fibroadenoma, while in multivariate analyses, duration of cigarette smoking and daily vitamin C intake were both shown to have inverse associations with risk of fibroadenoma. Although fibroadenoma does share some risk factors with breast cancer, there is insufficient evidence to suggest that it represents a precursor state.