Historical development of psycho-oncology in Japan: From clinical observation to national cancer policy.

Psycho-oncology has emerged as a multidisciplinary field addressing the psychological, social, and behavioral dimensions of cancer. Although its development has been well documented in Western countries, Japan has followed a distinct trajectory shaped by its cultural context, healthcare system, and national cancer policy. Building on early clinical observations, epidemiological studies clarified the prevalence, determinants, and longitudinal course of psychological distress across the cancer trajectory. Communication-preference research subsequently informed the development of the SHARE communication framework, while patient-directed communication support using Question Prompt Lists promoted shared decision-making. Research on survivorship, end-of-life care, and supportive care further expanded psycho-oncology from the management of psychiatric disorders to comprehensive supportive cancer care. These scientific advances became increasingly integrated into national cancer policy following enactment of the Cancer Control Act. Overall, these developments illustrate how psycho-oncology in Japan evolved from clinical observation to evidence-based practice and ultimately became integrated into routine cancer care through implementation science and national cancer policy. Despite these advances, important challenges remain, including disparities in access to psychosocial care, a limited specialist workforce, and variability in the quality of patient-clinician communication, underscoring the need for continued implementation and quality improvement.