Impact of cancer and other causes of death on mortality of cancer patients: A study based on Japanese population-based registry data.

Cancer registry data provide a very important source of information for improving our understanding of the epidemiology of various cancers. In this work, we estimated the 5-year crude probabilities of death from cancer and from other causes for five common cancers, namely stomach, lung, colon-rectum, prostate and breast, in Japan, using population-based registry data. Based on data on 344 676 patients diagnosed with one of these cancers between 2006 and 2008 in 21 prefectures participating in the Monitoring of Cancer Incidence in Japan (MCIJ) and followed-up for at least 5 years, we used a flexible excess hazard model to compute the crude probabilities of death for different combinations of sex, age and stage at diagnosis. For tumours diagnosed at the distant stage, as well as for regional lung tumours, the vast majority of deaths at 5 years in cancer patients were attributable to the disease itself (although this proportion was only around 60% in older prostate cancer patients). For localised and most regional tumours, the impact of other causes of death on the total mortality increased with age at diagnosis, especially for localised breast, colorectal and gastric cancer. By allowing the partition of the mortality experience of cancer patients into a cancer- and an other-cause-specific component, crude probability of death estimates provide insight into how the impact of cancer on mortality might differ among populations with different background mortality risks. This might be useful for informing discussions between clinicians and patients about treatment options.