Quality of life (QOL) is a subjective assessment and is included among patient-re-ported outcome (PRO) studies. QOL is as important for cancer patients as objectiveassessments such as survival and response rates. However, PRO studies are more diffi-cult to conduct than are studies to assess objective data. Regarding QOL studies whichare important among PRO studies, first we describe QOL, which Dr. Hayashi promotedaiming to improve. Then we describe the methods of assessing QOL. Finally, we in-troduce a novel self-monitoring QOL intervention. In the methods of assessing QOL,Minimal clinically important difference (MCID) and response shift are major challengesamong the methods of assessing QOL. MCID enables recognition of the patient’s per-ceptions, as well as the clinical outcomes. It is important to consider response shift wheninterpreting actual change of QOL. In the introduction of novel self-monitoring QOLintervention, QOL assessments are often seen as being for research purposes, thoughQOL self-monitoring should also be implemented in daily clinical routines. QOL as-sessment is often used as an outcome measure in clinical trials, and cancer diagnosisand treatments affect patients’ QOL. However, medical personnel may not sufficientlyunderstand patients’ problems, including QOL. In advancing the study of QOL, it is afuture task to address how QOL assessment information is to be fed back to patients.