CD44s is useful in the differentiation of benign and malignant papillary lesions of the breast.

BACKGROUND/AIMS CD44s, the standard form of CD44, has been shown to be downregulated during malignant transformation of breast cancers. It has also been reported recently to be a useful marker in differentiating between benign and malignant papillary lesions of the breast, with high expression in the former. CD44s expression in benign and malignant papillary lesions was evaluated. METHODS CD44s expression was assessed by immunohistochemistry in 101 benign papillomas and 59 papillary carcinomas (seven invasive papillary carcinomas, 41 papillary ductal carcinomas in situ, and 11 ductal carcinomas involving papillomas). RESULTS Patients' age and tumour size were significantly different between the papilloma and papillary carcinoma groups (p < 0.0001). CD44s showed positive staining in 45 papillomas (45%) and five papillary carcinomas (8%), and the difference was significant (p < 0.0001). The myoepithelial cells, when present, were also positive for CD44s in both groups, with no observable differences. Using CD44s positive staining to differentiate between benign and malignant papillary lesions gives a sensitivity, specificity, and accuracy of 45%, 92%, and 62%, respectively. CONCLUSIONS CD44s may be useful as an adjunct in the evaluation of morphologically problematic cases of papillary lesion of the breast.