This study aimed to identify the CD24 and CD44 immunophenotypes within invasive ductal breast carcinoma (IDC) subgroups defined by immunohistochesmistry markers and to determine its influence on prognosis as well as its association with the expression of Ki-67, cytokeratins (CK5 and CK18) and claudin-7. Immunohistochemical expression of CD44 and CD24 alone or in combination was investigated in 95 IDC cases arranged in a tissue microarray (TMA). The association with subgroups defined as luminal A and B; HER2 rich and triple negative, or with the other markers and prognosis was analyzed. CD44+/CD24- and CD44-/CD24+ were respectively present in 8.4% and 16.8% of the tumors, a lack of both proteins was detected in 6.3%, while CD44+/CD24+ was observed in 45.3% of the tumors. Although there was no significant correlation between subgroups and different phenotypes, the CD44+/CD24- phenotype was more common in the basal subgroups but absent in HER2 tumors, whereas luminal tumors are enriched in CD44-/CD24+ and CD44+/CD24+ cells. The frequency of CD44+/CD24- or CD44-/CD24+ was not associated with clinical characteristics or biological markers. There was also no significant association of these phenotypes with the event free (DFS) and overall survival (OS). Single CD44+ was evident in 57.9% of the tumors and was marginally associated to grading and not to any other tumor characteristics as well as OS and DFS. CD24+ was positive in 74.7% of the tumors, showing a significant association with estrogen receptor, progesterone receptor and Ki-67 and a marginal association with CK18 and claudin-7. Expression of claudin-7 and Ki-67 did not associate with the cancer subgroups, while a positive association between CK18 and the luminal subgroups was found (P=0.03). CK5, CK18 and Ki-67 expression had no influence in OS or DFS. Single CD24+ (P=0.07) and claudin-7 positivity (P=0.05) were associated with reduced time of recurrence, suggesting a contribution of these markers to aggressiveness of breast cancer.

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