Introduction: In Chile, the cancer mortality rate ratio between older adults and individuals under 65 years of age is 12.14. This excess mortality may be attributed to cancer-specific factors or comorbidities commonly observed in older adults.

Objective: To compare the frequency of advanced clinical stages at diagnosis, for the five most epidemiologically significant malignant neoplasms – breast, prostate, lung, colorectal and gastric cancers – between older adults (≥65 years) and individuals between 40 and 64 years of age.

Methods: We conducted a retrospective study of health insurance beneficiaries, identifying new cases of breast, prostate, lung, colorectal and gastric cancers diagnosed between 2018 and 2022. Age-adjusted incidence rates and the proportion of advanced clinical stages (III and IV) were compared between older adults and younger individuals.

Results: The cancer incidence rate ratio between older and younger adults ranged from 1.77 to 6.315 (p < 0.0001). For lung, colorectal and gastric cancers, the majority of patients were diagnosed at advanced clinical stages. Conversely, for breast and prostate cancers, the proportion of advanced stages was 18.07% and 40.37%, respectively. Older adults exhibited a significantly higher risk of advanced-stage diagnosis only for gastric cancer.

Discussion: The incidence of major cancers was markedly higher among individuals aged 65 and older. However, there were no significant differences in the proportion of advanced clinical stages at diagnosis across most cancer types, except for gastric cancer. The elevated cancer-related mortality observed in older adults may be more closely associated with comorbid conditions rather than the stage at diagnosis.