Cancer in the Oldest‐Old in Super‐Aging Japan: Trends and Characteristics From National Registry Data

Globally, Japan has the largest proportion of individuals aged ≥ 85 years. However, epidemiological studies on cancer in this age group are limited. This study aimed to investigate cancer trends and characteristics among the oldest-old adults (aged ≥ 85 years) in Japan, using population-based national and prefectural cancer registry data on incidence, mortality, trends, stage, and treatment patterns, and compared them with those of young-old adults (aged 65-84 years). From 1995 to 2020, the number of cancer cases among the oldest-old increased more than four-fold, with a significant average annual percent change of +5.9% (confidence interval: 5.4-6.3), surpassing growth in both the overall and young-old populations, and accounting for 15.7% of all cases in 2020. The oldest-old showed higher proportions of skin and gallbladder/bile duct cancers, and rising proportions of breast and prostate cancers. The group was more likely to be diagnosed at unstaged or advanced stages of cancer. Aggressive treatment was less commonly administered to this group, even when the stage at diagnosis was similar to that in the younger-old patients. These findings highlight distinct epidemiological and clinical cancer trends in the oldest-old. Since cancer incidence among the oldest-old will likely continue to rise, targeted healthcare and policy interventions that consider the impact of this age group at both individual and societal levels are urgently needed. To address the needs of an aging population, reconsideration of prevention, detection, and management, including guidelines and specialist availability, is suggested. Moreover, Japan must consider further cancer research in this rapidly increasing population.