33rd Annual Scientific Meeting proceedings

Introduction
Integumentary mast cell tumor (MCT) is regarded as a biologically non-aggressive cancer in cats. However, nodal metastases have been recently reported in 20-58.8% of cases. The aim of this study is to assess the impact of regional (RLN) versus sentinel lymph node (SLN) extirpation in cats with MCT.

Materials and Methods
25 client-owned cats presented for MCT excision were retrospectively enrolled. Blinded RLN excision or SLN excision guided by near-infrared fluorescence (NIRF) or by radiopharmaceutical and methylene blue (MB) was performed concurrently. Retrieved variables were: signalment, number of MCT, location and number of excised SLN/RLN, correspondence or not between SLN and clinically expected RLN. Histopathological reports were revised for status of the node, tumor grade and margins.

Results
Six cats had multiple MCT, 19 had a single MCT. The RLN was excised in 18 cats, while in 7 the SLN was removed after mapping with NIRF (n=5) or radiopharmaceutical and MB (n=2). The SLN did not correspond to the RLN in 71.4% of cases. Multiple RLN were removed in 2/18 cats, and multiple SLN in 5/7 cats. At histopathology, all MCT were low-grade, excised with tumor-free margins. Metastases were detected in 53% of RLN and in 85.7% of SLN.

Discussion
Despite all MCT being low-grade, nodal metastases were frequently detected, suggesting that lymphadenectomy should be implemented in feline MCT. The high non-correspondence rate between the SLN and RLN, and the higher rate of nodal metastases encountered in SLN, suggest that SLN mapping could allow for a more accurate staging.