fHER2, PR, ER, Ki-67 and Cytokeratin 5/6 Expression in Benign Feline Mammary Lesions

SIMPLE SUMMARY: Feline mammary neoplasias are highly prevalent in domestic cats and present many similarities to their human counterparts. Since information about benign feline mammary lesions is still scarce and often controversial, studies using a wider panel of oncological biomarkers are necessary to understand their potential contribution to malignant lesions. This study analyzed 47 benign lesions from 27 queens, regarding the expression of estrogen and progesterone receptors (ER and PR, respectively), fHER2 protein and two malignancy indicators (Ki-67 and CK 5/6). Our results showed that most of the lesions were ER positive (91.5%), PR negative (63.8%), fHER2 negative (64.4%), Ck 5/6 negative (76.6%) and with a low Ki-67 index (78.7%). Additionally, significant correlations were found between younger ages and ER positivity and between larger lesions and negative PR status. Our results highlight the importance of estrogen receptors in the development of benign feline mammary lesions, further contributing to the development of preventive and monitoring strategies in feline mammary oncology. ABSTRACT: Biomarkers are essential in the characterization of neoplastic lesions and aid not only in the classification of the nature of the lesions, but also in the understanding of their ontogeny, development and prognosis. In cats, while mammary carcinomas are increasingly being characterized, information on their benign lesions is still scarce. Indeed, a better characterization of benign lesions could have an important role in unravelling mammary oncogenesis, similar to that in human breast cancer. Thus, in this study, the expression of five markers was analyzed in 47 benign mammary lesions (hyperplasia, dysplasia and benign tumors) collected from 27 queens. Dysplastic and hyperplastic lesions were the most common (41/47, 81.7%). Most of the lesions were classified as ER positive (43/47, 91.5%), PR negative (30/47, 63.8%), fHER2 negative (29/47, 64.4%), CK 5/6 negative (36/47, 76.6%) and with a low Ki-67 index (37/47, 78.7%). Statistical analysis revealed a correlation between younger ages and ER positivity (p = 0.013) and between larger lesions and negative PR status (p = 0.038). These results reinforce the importance of evaluating the expression of the ER status, prevalent in benign lesions, as a putative precursor in cancer progression.