Ductal carcinoma in situ of the breast with apocrine cytology: definition of a borderline category.

Papillary patterns of apocrine cells are frequent in benign breast biopsies and pose little diagnostic difficulty when the classic apocrine cytology is present. Dilemmas in diagnosis do occur, however, when the usual papillary patterns of hyperplastic apocrine epithelium are absent in hyperplastic lesion, particularly if it is extensive, presents more complex patterns, and/or lacks usual nuclear features. We classified lesions with nonclassic apocrine features into diagnostic categories to separate those with malignant potential from those that are truly benign. We selected 54 such cases sent in consultation over a 2-year period (1989 to 1991). We applied two sets of criteria: nuclear patterns (usual, borderline, and as seen in ductal carcinoma in situ) and extent of lesion (< mm, 4 to 8 mm, and > 8 mm). The cases were categorized into diagnostic groups defined by these criteria of extent of lesion and cytologic features. We believe that application of these criteria recognizing borderline features to unusual, apocrine lesions fosters reproducibility in diagnosis and thus predictability of clinical outcome. We found only 10 cases to fit into borderline categories after use of the two criteria. The clinical utility of this suggested diagnostic stratification will require follow-up studies for linkage of criteria to clinical outcomes.