Comparative features of ductal carcinoma in situ and infiltrating ductal carcinoma of the breast on fine-needle aspiration biopsy. 
To evaluate the usefulness of fine-needle aspiration biopsy of the breast in separating ductal carcinoma in situ (DCIS) from infiltrating ductal carcinoma, the authors reviewed 16 preoperative fine-needle aspiration biopsies from biopsy-proven exclusive DCIS and 39 fine-needle aspiration biopsies from infiltrating ductal carcinomas with or without an in situ component.  Seven (44%) of the DCIS and eight (21%) of the infiltrating ductal carcinomas had inadequate material for diagnosis on the aspiration biopsy.  Five (32%) of the DCIS and 29 (74%) of the infiltrating ductal carcinomas caused suspicion or had positive results for malignancy.  Four (25%) of the DCIS and two (5%) of the infiltrating ductal carcinomas showed atypical cells.  Morphologic features of the atypical or malignant cells in the adequate specimens from these two lesions were similar except that the cells from the infiltrating ductal carcinomas showed more irregular nuclear spacing (94% vs. 44%, P less than 0.01) and more pronounced nuclear overlapping (65% vs. 33%) than those from the DCIS.  In addition, the fine-needle aspiration biopsies of the DCIS tended to be hypocellular (less than 10 cells/10X) (44% vs. 6.5%, P less than 0.05) and to contain benign epithelial cells (22% vs. 6.5%) and macrophages (33% vs. 13%).  Although the suspicion of DCIS might be raised when hypocellularity, benign epithelial cells, and macrophages are noted in a fine-needle aspiration biopsy of the breast that has positive results or causes suspicion for malignancy, fine-needle aspiration biopsy cannot be relied upon to distinguish DCIS from infiltrating ductal carcinoma.