Proliferating activity in columnar cell lesions of the breast

With the introduction of mammographic screening, columnar cell lesions (CCLs) are observed more and more frequently because they are often associated with microcalcifications. Until now, the proliferative activity of these lesions has not been previously evaluated. Ki67 index was performed by immunohistochemistry in CCLs without atypia [columnar cell change (CCC) n = 20 and columnar cell hyperplasia without atypia (CCH without atypia) n = 20], flat epithelial atypia (FEA DIN1A n = 20), low-grade intraductal carcinoma (DIN1C n = 20), high-grade intraductal carcinoma (DIN 2-3 n = 20). Adjacent terminal duct-lobular unit (TDLU) of normal breast tissue served as control. Ki-67 index is extremely low and close in CCLs without atypia (CCC mean 0.1% and CCH mean 0.76%) and paradoxically is lower than in normal TDLU (mean 2.4%) (p < 0.001). In the FEA, in comparison with normal TDLU and CCLs without atypia, the Ki67 is higher (mean 8.2%) (p < 0.001) but extremely close to those of DIN1C (mean 8.9%) (p = 0.6 NS). Lastly, the Ki67 index is higher in DIN 2-3 (mean 25.4%) than in CCLs without atypia and FEA (p < 0.001). CCLs are disparate lesions having in common cells with columnar configuration but different proliferative characteristics. These data represent findings of biological interest which could help us to better understand these controversial lesions.