The validity of the mortality to incidence ratio as a proxy for site-specific cancer survival

The complement of the cancer mortality to incidence ratio [1-(M/I)] has been suggested as a valid proxy for 5-year relative survival. Whether this suggestion holds true for all types of cancer has not yet been adequately evaluated.

We used publicly available databases of cancer incidence, cancer mortality and relative survival to correlate relative survival estimates and 1-(M/I) estimates from Denmark, Finland, Iceland, Norway, Sweden, the USA and the Netherlands. We visually examined for which tumour sites 5-year relative survival cannot simply be predicted by the 1-(M/I) and evaluated similarities between countries.

Country-specific linear regression analyses show that there is no systematic bias in predicting 5-year relative survival by 1-(M/I) in five countries. There is a small but significant systematic underestimation of survival from prognostically poor tumour sites in two countries. Furthermore, the 1-(M/I) overestimates survival from oral cavity and liver cancer with >10% in at least two of the seven countries. By contrast, the proxy underestimates survival from soft tissue, bone, breast, prostate and oesophageal cancer, multiple myeloma and leukaemia with >10% in at least two of the seven countries.

The 1-(M/I) is a good approximation of the 5-year relative survival for most but not all tumour sites.