Estimation of life expectancy and the expected years of life lost in patients with major cancers: Extrapolation of survival curves under high-censored rates

Objectives: There exists a lack of extrapolation methods for long-term survival analysis when censored rates are high (25-50%). This study aimed at estimating life expectancy (LE) after the diagnosis of cancer and the expected years of life lost (EYLL) using a newly developed semiparametric method. Methods: Patients (n = 425,294) diagnosed with 17 different types of major cancer were enrolled. All of the patients were registered with the Taiwan Cancer Registry between 1990 and 2001; their survivals were followed through the end of 2004. The survival function for an age- and sex-matched reference population was generated using the Monte Carlo method from the life table of the general population. Lifetime survival of the cancer patients (up to 50 years) were obtained using linear extrapolation of a logit-transformed curve of the survival ratio between the cancer and reference populations. The estimates were compared with the results from the extrapolation of fitted Weibull models. Results: The 15-year survival, LE, and EYLL for 17 different types of cancer were determined, of which the LE of breast, cervical, ovarian, and skin cancers exceeded 15 years; nasopharyneal, leukemia, bladder, kidney, and colorectal cancers exceeded 10 years. Validity tests indicated that the relative biases of the extrapolated estimates were usually <5% under high censoring rates. Conclusions: The newly developed method is feasible and relatively accurate to project LE and EYLL, which could also be merged with data pertaining to quality of life, for a more detailed outcome assessment in the future.