Difference in net survival using regional and national life tables in Japan

1Introduction

The net survival rate of a cancer patient at a given time is estimated as the ratio of the observed survival rate to the expected survival rate of that individual, the latter being estimated from the probability of death derived from the life tables of the general population where the patients studied reside. The net survival rate of the group of cancer patients at a given time is the average of the individual net survival rates [1] .

Comorbidity is a serious issue for cancer patients, and several reports have shown a high prevalence of comorbid conditions among elderly cancer patients [2] . The number of cancer patients aged > 65 years is increasing [3] . Patients with cancer and comorbidities have poorer prognoses than those without comorbidity [4] because of its association with increased all-cause mortality [5] for elderly patients diagnosed with breast, lung, colorectal, prostate, or ovarian cancer. Therefore, many studies have been published on the effect of life table by using patients’ characteristics in relative survival. In the United States, Stroup studied the differences between relative survival calculated by the national life table and the state-specific life tables [6] .

There are disparities in cancer mortality rates among the 47 prefectures in Japan. Aomori Prefecture has been the highest in both cancer and all-cause mortality rates over the last 15 years [7] . Due to higher smoking and obesity rates in Aomori than in the national average [8] , cancer patients in Aomori may be more common in a comorbid condition of arteriosclerosis and chronic obstructive pulmonary disease relative to Japan. Thus, the net cancer survival rate of Aomori using the Aomori life table (NSA) could be higher than that obtained using the life table for the entirety of Japan (NSJ). For effective cancer controls, policymakers need to use a net survival rate based on a local life table if the difference in the net survival estimation between the two tables is large. This study aimed to estimate the magnitude of the difference in net cancer survival using the Aomori and Japanese life tables. Further, the effects of patient characteristics on the difference in net survival rates was also examined using sensitivity analyses.