Immunohistochemical evaluation of STAT3-p-tyr705 expression in feline mammary gland tumours and correlation with histologic grade

We describe the expression of pStat3-ser727 (signal transducer and activator of transcription 3 phosphorylated on serine 727) in normal, hyperplastic and neoplastic feline mammary gland tissue assessed by immunohistochemistry in 56 cats. The samples included 4 normal mammary non-lactating tissues, 13 hyperplastic lesions (9 lobular and 4 fibroepithelial) and 39 tumours (6 benign and 33 carcinomas). For immunohistochemistry, tissue sections were incubated with anti-pStat3-ser727 monoclonal antibodies and visualized with EnVision-DAB polymer. pStat3-ser727 positivity was quantified in a semi-quantitative manner, differentiating cytoplasmic and nuclear localization. Intense anti-pStat3-ser727 immunoreactivity was detected in epithelial neoplastic cells and in the fibro-component in two fibroepithelial hyperplastic lesions. The immunostaining was dot-like in the cytoplasm and homogeneous in the nuclei in both benign and malignant lesions. Statistically significant relations were observed between nuclear expression of pStat3-ser727 and the pleomorphism score (p = 0.006), mitotic activity (p < 0.0001), and histological grade (p < 0.0001). In contrast, no significant correlations were observed for cytoplasmic pStat3-ser727. These findings add new and interesting information on the potential role of the phosphorylated form of Stat3 in malignant lesions.