Surgical treatment variation in a prospective, randomized trial of chemoradiotherapy in gastric cancer: The effect of undertreatment

Background: Intergroup 0116 (Southwest Oncology Group 9008), a national, multicenter, two-armed, prospective, randomized trial of adjuvant postoperative chemoradiotherapy, has demonstrated significant benefit. Methods: We prospectively captured complete surgical information, including the treatment of various lymph node stations, for 553 of the 556 eligible participants in this trial. Before any survival analysis, we coded D level by using the Japanese general rules and used the Maruyama program to estimate the likelihood of disease in undissected regional node stations, defining the sum of these estimates as the Maruyama Index of Unresected Disease (MI). We analyzed survival with Cox multivariate regression. Results: Fifty-four percent of participating patients underwent D0 lymphadenectomy. The median MI was 70 (range, 0-429). In contrast to D level, MI proved to be an independent prognostic factor, even with adjustment for the potentially linked variables of T stage and number of positive nodes. We detected no significant interaction between surgical or pathologic variables and the favorable effect of adjuvant treatment, but the power to detect such interaction was generally low. Conclusions: MI, a measure of unresected regional nodal disease in gastric cancer, proved an independent predictor of survival. Surgical undertreatment, as observed in this trial, clearly undermined survival.