Background

Older patients with colon cancer have poorer cancer survival than middle-aged patients. Cancer management in older patients may be complex, and older patients are underrepresented in clinical trials. As a consequence, older adults with cancer are likely to receive suboptimal treatment. While age is an important prognostic factor, only a few population-based studies described the role of patient and clinical factors on age disparities in colon cancer survival per se. 

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.

Method

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.

Impact statement

Our study allowed a better description of age disparities in colon cancer survival. It also encourages further investigation of age disparities in survival from other cancers, and the effect of other factors, especially, treatment on age disparities in survival.