Distribution of Inflammatory Infiltrate in Feline Mammary Lesions: Relationship With Clinicopathological Features.

Inflammation is a frequent finding in feline mammary neoplasms. Recent research suggests that the presence and location of tumour-associated immune cells might play a significant role in the clinical outcome of feline mammary carcinomas. The present study aimed to characterise the overall inflammatory infiltrates in healthy, hyperplastic/dysplastic, benign and malignant lesions of the feline mammary gland, and to evaluate its association with clinicopathological features. Perilesional and intralesional inflammatory foci were evaluated in 307 lesions from 185 queens, and categorised according to its distribution and intensity. The presence, location and density of tertiary lymphoid structures were also assessed. A control group included 24 queens without mammary changes. The presence of intralesional and perilesional inflammatory infiltrate was observed in a majority of the lesions (80.8% and 90.2%, respectively), but differed according to the type of mammary lesion, being more remarkable in malignant neoplasms. Only scarce individual cells were observed in 28.1% of the normal mammary glands. Data analysis revealed statistically significant associations (p < 0.05) between the presence of a more prominent intralesional and perilesional inflammatory reaction and several clinicopathological features associated with worse prognosis, including clinical stage, tumour size, mitotic count, lymphovascular invasion and lymph node metastasis. Furthermore, tertiary lymphoid structures were significantly more frequent in tumours with an infiltrative growth and lymph node metastasis. According to our results, the inflammatory reaction present in different types of feline mammary lesions is associated with the development of more aggressive tumours.