Background/Aim: Patients diagnosed with cancer are expected to choose one or more treatment modalities after receiving corresponding explanations of the options. When making these choices, patients consider the effects of treatment and aspects related to their quality of life. These concerns can cause confusion and conflict owing to the complicated information provided by medical caregivers. The objective of the study was to identify perceptions of cancer treatment in patients with cancer and the decision-making factors affecting their treatment choices. Patients and Methods: In this observational (cross-sectional) study, an online questionnaire survey was administered to 194 Japanese cancer patients with treatment experience. Patient information, perceptions of explanations provided by healthcare professionals, treatment views, and reasons for treatment decisions were subjected to a simple tabulation. Content and factor analysis was conducted to determine important treatment selection elements. Results: Regarding treatment perception, 60.3% of respondents (n=117) considered treatment a financial and family burden, 47.4% (n=92) had concerns about physical pain, and 40.2% (n=78) were worried about increased stress. Regarding decision-making quality, 95.9% determined their preferred treatment within one week, 49.0% reported difficulties in making their decisions, and 83.0% chose their treatment themselves. Major decisive factors were prolonging life, opinions of medical staff, and accepting treatment risks (68.0%, 68.6%, and 60.3% of patients, respectively). The main attitudes toward treatment were anxiety, expectations of benefit, and expectations of support and care. Conclusion: SDM should enable patients to visualize the changes that their bodies will experience and include discussions on prognosis. Psychological care should be prioritized to alleviate anxiety and improve readiness for decision-making; attention should be paid to the extent and timing of information provision.