Cancer patients receiving chemotherapy will sometimes conceal their discomfort, but an excessive endurance for adverse drug reactions (ADRs) can lead to a poorer prognosis. The aim of this study was to clarify the association between ADR endurance and a preference of cancer patients for aggressive treatments. A cross-sectional study was undertaken of inpatients under 75 years of age receiving injectable systemic chemotherapy or oral chronic medications at hospitals in Japan. Subjects were asked to respond to a validated questionnaire to assess the extent of their ADR endurance and whether they would choose a novel, more aggressive therapy if their life expectancy was estimated at 2 years. Study participants were separated into the chemotherapy group (n = 36) and the non-chemotherapy group (n = 78). In the chemotherapy group, patients who had moderate ADR endurance scores were more likely to choose the new therapy (0-33, 34-67, and 68-100 points: 0.0, 54.5, and 27.3 %; χ (2) test, p = 0.15). Additionally, every patient on long-term chemotherapy (≥3 years) had high ADR endurance scores but did not choose the new, riskier treatment. In the non-chemotherapy group, the proportion of those choosing the new therapy was linearly associated with higher ADR endurance scores (25.9, 38.2, and 64.7 %; p = 0.04). Cancer patients may prefer aggressive therapies, even when self-estimations of ADR endurance are not very high, especially if they have been receiving chemotherapy for a short period of time. These patients should be observed with great caution.