Abstract
When the T-classification criteria of UICC's TNM system (1987) are applied to a gingival carcinoma with no special modifications, most gingival carcinoma may be classified as T4 because gingival tissue is so thin that a carcinoma on the gingiva can easily to reach the underlying bone tissue, Several modifications of T4 criteria have been proposed to rectify this situation.
According to the following criteria. T classification was made on 26 patients with gingival carcinoma of the lower jaw who had visited our clinic and had received no previous treatment for the concerned carcinoma: (1) the original T-classification criteria of UICC; (2) modified criteria A proposed by the Japanese Association for Head and Neck Tumors, which indicates that a tumor is classified as T4 when the tumor invades more deeply than the alveolar bone; (3) modified criteria B, which indicates that a tumor is classified as T4 when the tumor invades deeply enough to reach the mandibular canal. The other criteria for T1-3 in the modified criteria A and B are the same as the original criteria of UICC.
Individual T-classification criteria were compared involving their appropriateness for clinical use, and the following results were obtained: (1) Modified criteria B showed the most well-balanced distribution of patients for each T category. (2) Significant differences in cumulative survival rates (Kaplan-Meier's method) were found between the T2 and T3 groups, as well as between the T2 and T4 groups for modified criteria B (log rank test, p<0.05) . As a result, modified criteria B were felt to be the most practical for clinical use.
