Evaluation of splenic and hepatic mast cell numbers in dogs with cutaneous mast cell tumors independent of histological tumor grade

Introduction Canine cutaneous mast cell tumors (cMCTs) are the most common skin tumors of the dog, representing up to 21 % of all cutaneous neoplasms. As their biologic behavior is highly variable, adequate staging is essential for further therapeutic decisions. Although, the necessity of fine-needle aspiration (FNA) of the spleen and liver, especially in lower grade tumors (Patnaik grade I/II and Kiupel low grade) is still subject to debate.

Objective The aim of this study was to determine the number of mast cells (MCs) in the spleen and liver in dogs with cMCTs of all histological grades and to investigate their association with survival time.

Methods Cytological spleen and liver samples collected at our institution from dogs with cMCTs between May 2007 and December 2018 were reevaluated and the number of MCs per low-power field (10× objective) that were not associated with connective tissue was noted. Four groups were created: none (no MCs), rare (occasional scattered, individualized MCs), low (< 5 individualized MCs), and high/cluster (> 5 individualized or clusters of MCs).

Results In total 104 dogs were evaluated. Spleen samples from 100 dogs were included and 28 %, 56 %, 13 %, and 3 % were classified as none, rare, low, and high, respectively. A significant difference in the tumor-specific median survival time (TS-MST) (p < 0.0001) between the 4 groups (not reached vs. 2180 vs. 899 vs. 37 days) was noted. Fifty-two liver samples were evaluated with 50 %, 37 %, and 13 % belonging to none, rare and low groups, respectively. There was no significant difference in the TS-MST (p = 0.99) between 3 groups (not reached vs. not reached vs. 1426 days). The majority of tumors were Patnaik grade I/II (74 %), or low-grade (64 %) MCTs.

Conclusion The data shows that in our population the dogs with an increasing number of splenic MCs survived significantly shorter than the dogs with no or occasional splenic MCs. As such, the results suggest that evaluation of splenic MCs might be needed even in lower grade tumors. However, the evaluation of MCs in the liver is inconclusive, as the high/cluster group was not represented.

Publication History

Article published online:
15 February 2021