Introduction

Canine mast cell tumors (cMCTs) vary in their biological behavior, treatment, and prognosis, based on their grade. Immune cell infiltration has been associated with prognosis and response to treatments in some human cancers, and immune-targeting therapeutics are increasingly being explored in veterinary oncology. However, currently little is known about the immune microenvironment in low- and high-grade cMCTs. Therefore, the objective of this study was to determine the prevalence of T lymphocytes, T regulatory lymphocytes, and macrophages, in low- and high-grade cMCTs.

Methods

The Louisiana Animal Disease Diagnostic Laboratory (LADDL) database was searched for cases of cMCTs. Twenty-five low-grade and 25 high-grade formalin-fixed paraffin-embedded cMCT samples were identified.

Immunohistochemistry (IHC) was performed to detect CD3, FoxP3, and Iba1 on sequential sections. Three 400x fields with the highest numbers of CD3+ cells were identified for each tumor. The percentage of CD3+, FOXP3+, and Iba1+ cells was quantified in each of these three “hot-spot” fields using ImageJ software.

Results

Immune cell infiltrates in five high-grade and four low-grade cMCTs have been quantified so far. Numerically higher average

Conclusion

T lymphocytes and macrophages may be increased in high-grade, compared to low-grade cMCTs, although analysis of remaining samples will be needed to determine if statistical significance exists between groups. Increased immune infiltrates in high-grade tumors may indicate that the immune microenvironment plays a role in the aggressive behavior of high-grade cMCTs.