Weishaar's classification system for nodal metastasis in sentinel lymph nodes: Clinical outcome in 94 dogs with mast cell tumor

Abstract Background The therapeutic role and prognostic relevance of lymphadenectomy in mast cell tumor (MCT) has historically been evaluated on regional rather than sentinel lymph nodes. Hypothesis/Objectives To update information about the association of histological nodal (HN) classes with clinical outcome in dogs with MCT after tumor excision and extirpation of normal‐sized sentinel nodes (SLN) guided by radiopharmaceutical. Animals Ninety‐four dogs with histologically‐confirmed treatment‐ naïve MCT (71 cutaneous, 22 subcutaneous and 1 conjunctival MCT) were included if without: distant metastases, lymphadenomegaly, concurrent mixed cutaneous, and subcutaneous MCT. Methods This was a monoistitutional cohort study. Tumors characteristics were retrieved and SLNs were classified according to Weishaar's system. Incidence of MCT‐related events (local, nodal, distant relapse), de novo MCT or other tumors and death (MCT‐related and non‐MCT‐related), were recorded. Incidence curves were compared among the HN classes. Results Twenty‐seven dogs had HN0, 19 HN1, 37 HN2, and 11 HN3 SLN. Thirteen (2 HN0, 4 HN2, and 7 HN3) received adjuvant chemotherapies. Kiupel high grade, increasing number of SLN and lymphocentrums were associated with higher HN classes. Five dogs died for MCT‐related causes: 1 low‐grade (HN0) and 1 subcutaneous (HN3) had a local relapse, 2 high‐grade had distant relapse (HN3‐HN0) and 1 dog developed disease progression from a de novo subcutaneous MCT. No nodal relapse was registered. Fourteen dogs developed de novo MCTs. Conclusion/Discussion Low grade/low‐risk MCT with nonpalpable and normal sized SLN have a favorable outcome independently from the HN. Result should be considered strictly related to the successful SLN detection guided pre‐ and intraoperative by radiopharmaceutical markers.