Muscle invasion in oral tongue squamous cell carcinoma as a predictor of nodal status and local recurrence: just as effective as depth of invasion?

Tumor depth of invasion (DOI) is a histologic feature that consistently correlates with lymph node metastasis; however, there are many difficulties with accurately assessing DOI. The aim of this study was to identify a simpler and more reproducible method of determining DOI, by using skeletal muscle invasion as a surrogate marker of depth. Oral tongue squamous cell carcinoma American Joint Committee on Cancer (AJCC) stage T1 cases were identified in the Emory University Department of Pathology database. 61 cases, with a minimum of 2 years of follow-up, were included in the study. Cases were examined histologically to assess muscle invasion and DOI. The two methods of measurement were analyzed to determine the positive predictive value (PPV) of DOI or muscle invasion for both nodal disease and local recurrence. Cases with muscle invasion had a 23.3% PPV of occult lymph node metastasis. Cases with DOI of greater than 3 mm had a 29.7% PPV of occult lymph node metastasis. Cases with muscle invasion had a 43.7% PPV of local tumor recurrence. Cases with maximum DOI of greater than 3 mm had a 40.4% PPV of tumor recurrence. Although the PPV of muscle invasion in regards to nodal status was slightly less than DOI, it represents a more easily reproducible parameter which could guide surgeons in determining if the case warrants an elective neck dissection in a cN0 (clinically negative) neck. Interestingly, the PPV of local recurrence was higher with muscle invasion than DOI, and may represent an important indicator for extent of resection.