Lymph Node Status in Canine Mast Cell Tumors

In the Literature

Ferrari R, Marconato L, Buracco P, et al. The impact of extirpation of non-palpable/normal-sized regional lymph nodes on staging of canine cutaneous mast cell tumours: a multicentric retrospective study. Vet Comp Oncol. 2018;16(4):505-510.

The Research …

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

… The Takeaways

Key pearls to put into practice:

• Palpation characteristics are an insensitive method for detecting metastatic disease in MCTs and many other cancers.

• The use of the Patnaik 3-tier⁸ and Kiupel 2-tier⁹ histologic grading systems in this study highlights a problematic issue with the Patnaik system. Patnaik grade II MCTs are the most common MCT classification¹⁰; however, this study found discrepancies between the Patnaik grade II classification of some lymph nodes when they were compared with the Kiupel grading system. These discrepancies create a gray area in how to manage Patnaik grade II MCTs.

• Removal of the regional lymph node with MCT resection may yield a high rate of metastatic disease, as seen in this study.

• Larger MCTs (>3 cm) have a higher rate of nodal metastasis.