The impact of timely cancer diagnosis on age disparities in colon cancer survival in New Zealand

Objective: We described the role of patient-related and clinical factors on age disparities in colon cancer survival among patients aged 50-99 using New Zealand population-based cancer registry data linked to hospitalization data. Design: We included new colon cancer cases diagnosed between 1 January 2006 and 31 July 2017, followed up to 31 December 2019. We linked these cases to hospitalisation data for the five years before the cancer diagnosis. We modelled the effect of age at diagnosis, sex, deprivation, comorbidity, and route to diagnosis on colon cancer survival by stage at diagnosis (localized, regional, distant, missing). Results: Net survival decreased as the age at diagnosis increased, notably in advanced stages and missing stage. The excess mortality in older patients was minimal for localised cancers, maximal during the first six months for regional cancers, the first 18 months for distant cancers, and over the three years for missing stages. The age pattern of the excess mortality hazard varied according to sex for distant cancers, the route to diagnosis for regional and distant cancers, and comorbidity for cancer with missing stages. Conclusion: The present population-based study shows that factors reflecting timeliness of cancer diagnosis most affected the difference in survival between middle-aged and older patients, probably by impacting treatment strategy. Because of the high risk of poor outcomes related to treatment in older patients, efforts made to improve earlier diagnosis in older patients are likely to help reduce age disparities in colon cancer survival in New Zealand.