Analysis of human mammary fibroadenoma by Ki-67 index in the follicular and luteal phases of menstrual cycle

Fibroadenoma is the most common benign mammary condition among women aged 35 or younger. Expression of Ki-67 antigen has been used to compare proliferative activity of mammary fibroadenoma epithelium in the follicular and luteal phases of the menstrual cycle. Ninety eumenorrheic women were selected for tumour excision; they were assigned to either of the two groups, according to their phase of menstrual cycle. At the end of the study, 75 patients with 87 masses were evaluated by epithelial cell Ki-67 expression, blind (no information given concerning group to which any lesion belonged). Both groups were found to be homogeneous relative to age, menarche, body mass index, previous gestation, parity, breastfeeding, number of fibroadenomas, family history of breast cancer and tabagism. Median tumour size was 2.0 cm and no relationship between proliferative activity and nodule diameter was observed. No typical pattern was observed in the expression of Ki-67 in distinct nodules of the same patient. Average values for expression of Ki-67 (per 1000 epithelial cells) in follicular and luteal phases were 27.88 and 37.88, respectively (P = 0.116). Our findings revealed that proliferative activities in the mammary fibroadenoma epithelium did not present a statistically significant difference in the follicular and luteal phases. The present study contributes to clarifying that fibroadenoma is a neoplasm and does not undergo any change in the proliferative activity during the menstrual cycle.