Identifying lymph node status in mast cell tumors (MCTs) is important for determining prognosis and whether further staging is necessary. Although palpation and cytology of regional lymph nodes are often performed, their value is limited; thus, histopathology remains the gold standard.1-3 It is generally understood that enlarged lymph nodes should be removed in all cases, but less is known regarding how to manage lymph nodes that are normal in size or nonpalpable, as well as how to definitively diagnose metastatic disease on histopathology. A recent study categorized lymph nodes as HN0 (nonmetastatic), HN1 (premetastatic), HN2 (early metastasis), or HN3 (overt metastasis), according to the degree of metastatic cell aggregates present and evaluation of lymph node architecture.4
In the current study, the authors aimed to assess the metastatic rate of nonpalpable or normal-sized regional lymph nodes in dogs with MCTs. Included in the study were 93 dogs with solitary cutaneous MCTs that were negative for distant metastasis. Regional lymph nodes that were nonpalpable or normal in size were removed, and clinical characteristics, including tumor size and histologic grade, were evaluated. Of the 93 dogs, 46 were found to have histologically detectable metastatic disease. The only clinical factor significantly associated with metastatic disease was a tumor diameter >3 cm.
These study findings highlight the importance of regional lymph node removal at the time of MCT removal. Lymph node status is important for staging and potential chemotherapy decision-making and may also guide the need for further staging, as MCTs tend to metastasize to the regional lymph nodes before becoming widely metastatic.5 Removal of metastatic lymph nodes may also provide a survival advantage.6 Regional lymph node removal was a high-yield test in this study; however, further investigation is needed to determine whether sentinel lymph node mapping would be a more effective method of staging.7
