Prognostic Factors for Survival According to Treatment Period in Oral Squamous Cell Carcinomas

The purpose of this study was to assess changes in prognostic factors related to modification of surgical treatment on the basis of grade of tumor malignancy and to contribute to improved surgical treatment of patients with oral squamous cell carcinoma. Fourhundred three patients with oral squamous cell carcinoma treated by surgery were classified according to treatment period as follows: f irst period, 1976-1986; second period, 1987-1991; and third period, 1992-1997.Three and 5-year cumulative disease-specific survival rates according to treatment period were as follows: first period (n=187), 78.6, 76.3%; second period (n=113), 76.6, 73.7%; and third period (n=103), 88.9, 87.2%. On univariate analysis of survival according to T, N, stage, growth pattern, and mode of invasion, significant differences (P<0.05) were found for all characteristics in the first and second periods, while in the third period no significant difference was found for growth pattern or mode of invasion.Cox regression analysis of disease-specific survival identified the following as independent prognostic factors: mode of invasion (1+2, 3, 4C+4D), growth pattern (exophytic, endophytic), and N (0, 1, 2) in the first period, mode of invasion (1-3, 4C+4D) and N (0, 1, 2+3) in the second period, and only N (0, 1, 2) in the third period.Owing to the improved outcome for highly invasive carcinoma, the prognostic values during the third period differed from those during the first and second periods.