Palpation of enlarged lymph nodes is often assumed to be indicative of primary or metastatic disease. This study evaluated 100 dogs with histologically confirmed oral malignant melanoma. The presence of metastatic disease in regional lymph nodes was checked for, and mandibular lymph node size was evaluated to see if node size alone is an accurate and reliable means of tumor staging. Dogs were categorized into two groups: those without metastatic lymph nodes (47, or 47%) and those with metastatic lymph nodes (53, or 53%). Of the 47 dogs that had no evidence of metastasis, 23 dogs (49%) had enlarged mandibular lymph nodes and 24 (51%) had normal-sized nodes. However, of the 53 dogs with evidence of mandibular lymph node metastasis, 37 (70%) had enlarged nodes and 16 (30%) had normal-sized nodes. Of the 40 dogs from both groups that had normal-sized nodes, 16 (40%) had microscopic evidence of disease. These results suggest that lymph node size as a predictor of metastasis is insufficient for clinical staging of malignant melanoma.

COMMENTARY: This study emphasizes the importance of cytologic and/or histologic evaluation of regional lymph nodes for accurate staging of oral neoplasia. Three lymphocentrums drain the oral cavity, so it is important to perform a thorough evaluation because the superficial mandibular nodes alone may not provide the most accurate information. If surgical resection is performed, intraoperative evaluation along with sampling of nodes from all three lymphocentrums may provide more complete information, especially for this tumor type.

Association between lymph node size and metastasis in dogs with oral malignant melanoma: 100 cases (1987-2001). Williams LE. JAVMA 222:1234-1236, 2003.