Use of p63 and CD10 in the differential diagnosis of papillary neoplasms of the breast

Papillary neoplasms of the breast represent a complex spectrum ranging from benign to malignant lesions. The myoepithelial cell (MEC) layer is generally continuous in papillomas and increasingly discontinuous to absent in atypical and malignant counterparts. Identification of MECs can be difficult on morphological grounds and currently relies on immunomarkers. We investigated the potential role of p63 and CD10 in 20 papillary lesions and compared them with 1A4 and calponin. In 18 cases, adjacent normal breast tissue was available for study. All four markers were diffusely positive in all samples of normal tissue and benign papillomas indicating similar sensitivity in the identification of MECs. Intense positivity was found in 100% of the cases with 1A4 and CD10, but in only 76% with calponin and in 60.5% with p63 (differences statistically significant, p < 0.05), suggesting that the former two render more reproducible results. The most specific markers were p63 and CD10 which showed cross-reactivity in 0% and in up to 33% of the cases respectively. 1A4 and calponin showed diffuse cross-reactivity in all cases. When assessing benign versus atypical papillomas, the best parameters were diffuse positivity using CD10 or p63, and continuous MEC layer, mainly using CD10. When comparing benign papillomas to carcinomas all parameters were equally useful with 1A4 and CD10. Regardless of the marker, intense positivity was the only parameter that could distinguish atypical papillomas from papillary carcinomas. p63 staining, which renders a nuclear and mostly discontinuous reactivity, was not as useful as the other markers when the parameter continuous MEC layer was evaluated. Although CD10 seems to combine the highest specificity and reproducibility with a good sensitivity, reproducibility of 1A4 is higher. Thus, a minimum panel to assess papillary lesions should include both markers. Although p63 is the most specific, its nuclear and discontinuous pattern may lead to erroneous diagnosis, especially in the differentiation between benign papillomas and atypical/malignant lesions.