CD44+/CD24– Cancer Stem Cells Are Associated With Higher Grade of Canine Mammary Carcinomas

The CD44þ/CD24– phenotype identifies cancer stem cell (CSC) properties in canine mammary carcinoma (MC); however, the histopathological features associated with this phenotype remain to be elucidated. Here, we determined whether the CD44þ/CD24– phenotype was associated with hormonal receptor (HR; estrogen receptor [ER] and/or progesterone receptor [PR]) status and/or triple (ER, PR, and human epithelial growth factor receptor 2)–negative (TN) subtype; conventional histological evaluation was also performed. We found that, as single markers, both CD44þ and CD24þ were associated with less aggressive histological types, low grade, and a non-TN subtype; both markers were associated with HR positivity. On the other hand, a CD44þ/CD24– phenotype was associated with higher grade of carcinoma. Therefore, our results suggest that immunohistochemical phenotyping for CD44/CD24 is useful for the evaluation of tumor behavior as well as CSC-like properties in canine MCs.