Affect on survival per increase in each millimeter of tumor depth in tongue cancer

The critical tumor depth at which the risk of occult metastasis increases in tongue cancer has been demonstrated as ≥4-5 mm. Conventional T staging might not be an accurate predictor for survival in situations wherein infiltrative growth pattern is easily overlooked. Thus risk of death associated with increase in tumor depth per millimeter might be useful to understand patient's disease status during follow up. Historical cohorts of patients with pT1N0 and pT2N0 primary squamous cell carcinoma of tongue treated between January 2010 and December 2011 were selected and analyzed in univariate and multivariate cox-regression model to indicate the risk of death associated with an increase in each millimeter of tumor depth. The median period of follow up was 34 months. Total 67 patients fulfilled the above mentioned criteria, among them 11 patients died by the end of study period. The mean (SD) age of the patients studied was 49.7 (12.7) years and their age ranged from 21 to 74 years. Among these 66 % (n = 44) were males. In the univariate log-rank test, margin status (p = 0.016), t-stage (p = 0.018) and increased tumor depth (p < 0.0001) were risk factors for occurrence of death. When adjusted for other risk factors in the multivariate cox-regression model, per one unit increase of tumor depth (mm) there was 1.07 (95 % CI 0.95, 1.21) units increased risk of death. Depth of tumor with increase in each millimeter in tongue cancer appears to be associated with risk of death irrespective of regional lymphatic spread.