Aims: Male breast cancer represents - mor aggressiveness and drug resistance. CSCs are characterized by CD44 and/or ALDH1 expression. In this study, we investigated their expression in male breast cancer. Method: Two in situ ductal carcinoma (DCIS) and 18 invasive duc- tal carcinoma (IDC) male breast cancer cases were studied with Jefferson IRB approval. Membrane staining of CD44 was scored by the percentage of positivity. Cytoplasmic expression of ALDH1 was considered positive. Results: Ten cases had high CD44 expression, which were all IDC. Both DCIS and in situ component of IDC were CD44 low. ALDH1 was only positive in 15 IDCs. ALDH1+ cells were mostly in the invasive component. Both DCIS cases were negative for ALDH1. Among the 15 ALDH1+ IDCs, five with only invasive component had a higher percentage (aver- age 4.4%) of positive cells compared to the other eight with in situ components (average 2.0%). Metastatic cells in sen- tinel lymph nodes had a similar expression pattern of CD44 and ALDH1 as their primary tumor. Conclusion: CD44 and ALDH1 are expressed in male breast cancers and they are overexpressed in invasive cancer compared to carcinoma in situ. These findings suggest that CSCs play an important role in the progression to invasive carcinoma.
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