Canine oral melanoma is a common, aggressive tumor with limited treatment options. Tumor-infiltrating lymphocytes (TILs) are important in antitumor immunity. This study used histopathology and immunophenotyping by flow cytometry to evaluate the presence and distribution of TILs in canine oral melanoma, including the frequency of CD8+ T cells, CD4+ T cells, and regulatory T cells. Fifty samples of oral melanoma from 45 dogs that did not receive treatment prior to surgery were included in the study. The distribution of TILs in the tissue (brisk, nonbrisk, and absent) was evaluated in 48 samples. Twenty-eight (58%) samples had a brisk distribution pattern, 10 (21%) samples had a nonbrisk pattern, and 10 (21%) samples had an absent TIL pattern. Comparing the histological evaluation and the immunophenotyping data, it was observed that samples with a brisk TIL pattern had a higher frequency of CD8+ T lymphocytes (P = .05) and a lower frequency of CD4+/CD25+/FoxP3+ Tregs (P = .03), compared to the samples with nonbrisk and absent infiltrate patterns. Patients with a higher survival rate had higher TIL scores (P = .002), a brisk or nonbrisk TIL pattern (P = .001), and an increased frequency of CD8+ T lymphocytes infiltrating the tumor (P = .003). Our analysis suggests that the evaluation of TILs in canine oral melanoma is relevant to predict tumor aggressiveness and patient prognosis.
Keywords: T lymphocytes; dogs; melanoma; regulatory T cells; tumor microenvironment; tumor-infiltrating lymphocytes.