Differential CD133 expression distinguishes malignant from benign papillary lesions of the breast.

Malignant papillary lesions are, in contrast to their benign counterpart, rare malignant tumors in the breast. To differentiate between benign or atypical and malignant papillary lesions can be difficult, especially in core biopsy specimens. In the present study, excisional or more extensive surgical specimens of 33 papillary carcinomas, 2 micropapillary carcinomas, and 17 atypical papillomas of the breast were reviewed and classified according to the latest WHO classification. Thirty-three intraductal papillomas and 49 invasive carcinomas, no special type (NST), were included in the study for comparison. CD133 expression in papillary carcinomas was significantly lower than that in benign and atypical papillomas (p < 0.001). CD133 expression in invasive carcinoma NST was also significantly higher than that in papillary carcinomas. Our data suggests that absence of expression of CD133 can be a useful marker in the differential diagnosis between malignant papillary lesions and their benign or atypical mimics. The characteristic loss of CD133 expression in papillary carcinomas of the breast also indicates that these lesions are distinct from other types of breast cancer.