The importance of adding quality of life (QL) evaluation in cancer research has been emphasised inrecent years. This document provides a summary of the findings of research on cancer patients' quality of life.According to descriptive research, cancer therapy appears to reduce the quality of various areas of life. Thefindings of research comparing two or more groups of cancer patients are inconsistent. The anticipation thatparticular treatment methods will have a detrimental impact on patients' QL is validated in some research but notin others. Even the premise that cancer patients have lower QL than the general population is unsubstantiated.This research provides reasons for these surprising outcomes. To begin, the definition and operationalizationof the notion QL varies from research to study. QL may relate to an overall evaluation or to the evaluation ofspecific areas of life, as well as to the patient's subjective experience or the appraisal of the situation by others.Second, various methodological issues, particularly those related to reliability, validity, and design, are discussed.Finally, it is proposed that psychological mechanisms may account for the lack of differences between cancerpatients and others, and therefore, theoretically, explain the documented inconsistencies.