Health indices for disease incidence risk and duration in the Semi-Markov setting

Over the last decade, the number of years of life lost (YLL) became a popular tool in biostatistics and epidemiology to measure discrepancies in life expectancy or mortality between a cohort of patients and the general population. Its prominence in the literature is primarily due to its ease of interpretation and because information on the cause of death is not required. Moreover, multi-state models are a powerful statistical approach to study the evolution of individuals between several "states". Derived from data collected by the Belgian Cancer Registry, encompassing 161,007 cases of melanoma, thyroid, and female breast cancer, a three-state (healthy-cancer-death) illness-death model is used to illustrate how it can be applied to cancer registry data to estimate the incidence risk, and the number of years of life lost due to cancer at different ages at diagnosis and given that the patient survived some years after diagnosis. Results suggest that the probabilities of being diagnosed with cancer over the next 20 years for a healthy individual remain rather low for melanoma and thyroid cancers for both sexes, but considerably increases with age for female breast cancer. Results also suggest that, for female breast cancer, the number of years of life lost before the age of 70 years due to cancer is highest when diagnosed at young ages and then decreases with age at diagnosis, whereas for melanoma and thyroid cancers, it peaks when diagnosed at later ages (between 35 and 55 years depending on the cancer and sex). It also turns out that the number of years of life lost before the age of 70 due to cancer is larger for men than for women for both melanoma and thyroid cancers. Last, it is found that, for melanoma and thyroid cancer patients diagnosed between the age of 20 and 70 years, once they have survived their cancer for 10 years, the number of years of life lost before the age of 70 due to cancer remains below one year. This indicates that, up to the age of 70 years, these patients lose a limited number of years of life due to cancer compared to the general population.