[Pathological characterization of atypical ductal hyperplasia of the breast].

To clarify the pathological features of atypical ductal hyperplasia (ADH) defined by Page's criteria, histological patterns and the extent of 17 lesions of ADH including clinging carcinoma were examined. The nuclear measurements (mean nuclear area and irregularity of nuclear shape) and the MIB-1 labeling index of ADH were compared with those of noncomedo DCIS with lower grade nuclei, and usual ductal hyperplasia (DH). All ADH were classified into cribriform or micropapillary/clinging types. The extent of ADH was always less than 2.5 mm in the cribriform type (1.4 mm in average), against 5 mm or greater in 6 of 8 lesions of the micropapillary/clinging type (7.1 mm in average). Nuclei of ADH tended to be smaller (< or = 8 microns) than DH and DCIS (p < 0.05), and less irregular in shape than DH (p < 0.01), although indistinguishable from lower grade nuclei of DCIS using these parameters. The MIB-1 labeling index of ADH was very low (0-2.3%) and was the best parameter to distinguish from DCIS (p < 0.01). It was also suggested that the lower level of proliferative activity is one of the most distinctive features of ADH.