['Effective adjuvant chemotherapy (Adj.C) for completely resected non-small cell lung cancer (NSCLC) was recently established. However, there may be some unresolved adverse effects, as have been observed in early stage populations or long-term survivors after other types of Adj.C. The substantial risk in such patients was examined by a mathematical method.', 'Variables X and Y were defined by two outcomes of Adj.C: X = the ability to eliminate micro-metastasis and Y = the development of effects that threaten life. Then, the following formula was generated: Survival benefit = (death rate) X - (death rate) X Y - (survival rate) Y. We then solved for X and Y and verified our findings using reported data from clinical trials.', 'By solving two simultaneous equations for the formula applied to the data for stage (1) IA and (2) IIIA in the LACE study (J Clin Oncol 26:5043-5051, 2008), X and Y were 2.6 and 1.9, respectively. When these values were applied in the formula for stage IB patients in the same study, the theoretical (-2.3 %) and reported values (2.5 %) were close. When these were applied for stage IB-IIIA patients in the IALT study (N Engl J Med 350:351-360, 2004), the theoretical (5.0 %) and reported values (4.1 %) were also similar.'] Does substantial risk affect the stage-dependent outcomes of cisplatin-based adjuvant chemotherapy for completely resected non-small cell lung cancer?