Ki-67 expression in sclerosing adenosis and adjacent normal breast terminal ductal lobular units: a nested case–control study from the Mayo Benign Breast Disease Cohort

Sclerosing adenosis (SA) increases risk for invasive breast cancer (BC) 2.1 times relative to that in the general population. Here, we sought to evaluate whether the proliferation marker Ki-67 stratifies risk among women with SA. A nested case–control sample of patients with SA was obtained from the Mayo Clinic Benign Breast Disease Cohort. Ki-67 expression was evaluated in SA lesions and in the adjacent normal terminal duct lobular units (TDLU) in women who did (cases, n = 133) or did not (controls, n = 239) develop BC. Ki-67 was scored by intensity and number of positively stained cells per one high-power field (magnification, ×40) (40× HPF) for both SA and normal TDLU. Associations of Ki-67 expression with case–control status were assessed using conditional logistic regression. Higher Ki-67 expression was significantly associated with case–control status in both SA (P = 0.03) and normal background TDLU (P = 0.006). For the SA lesion, >2 average positively stained cells/40× HPF showed an adjusted odds ratio (OR) of 1.9 (95 % CI, 1.1–3.4) compared to samples with an average of ≤2 positively stained cells. For background TDLU, lobules with >2 but ≤6 average positively stained cells showed an adjusted OR of 1.3–1.5, whereas those with an average of >6 positively stained cells had an OR of 2.4 (95 % CI, 1.1–5.3) compared to those with an average of <2 positively stained cells. Among women with SA, increased Ki-67 expression in either the SA lesion or the normal background TDLU carried an approximately twofold increased odds of subsequent BC as compared to lower Ki-67 expression.