Mast cell tumors (MCT) are histopathologically graded in two ways; using either the Patnaik or Kiupel grading systems, and often with both. The first system consists of three levels where grade 1 is considered a well-differentiated tumor, grade 2 as intermediate, and grade 3 as an undifferentiated tumor, thus the most aggressive. Kiupel has only two grades; low-grade and high-grade. In one study, pathologists placed 85% of grade 2 tumors in Patnaik’s system as low-grade in the Kiupel system. Another study showed that 30% of grade 2 Kiupel tumors had metastasized to the local lymph node at the time of diagnosis. There is no doubt that Kiupel grade 2 MCT is a serious diagnosis!
In the latest issue of the Journal of Small Animal Practice, a research group has published a multi-institutional study examining the benefits of removing the local lymph node when a dog presents with a Kiupel grade 2 mast cell tumor. The study is retrospective, and 49 dogs with MCT metastasis to lymph nodes were included. All had the tumor removed with at least a 2 cm margin and simultaneously underwent a protocol using vinblastine, prednisolone, and toceranib, as well as treatment for any paraneoplastic conditions. 18/47 dogs did not have the lymph node removed simultaneously, and there was a statistically significant difference in survival in these dogs compared to those who had the lymph node removed (29/47); 250 versus 371 days (median value). Furthermore, the group found that the risk of tumor progression locally and in the lymph node, and tumor-related death was several times higher in the group that did not have the lymph node removed. The tumor’s size was, not surprisingly, correlated with the risk of local recurrence.
Even with a retrospective and relatively small study, I think we can safely say that it can be beneficial to stage MCTs before surgery, and also to remove the lymph node while at it. It doesn’t take much longer, and is well worth it if the patient can gain a few extra months in lifespan.
More information for the curious:
https://doi.org/10.1111/jsap.13525
