Are hospitals in Japan with larger patient volume treating younger and earlier-stage cancer patients? An analysis of hospital-based cancer registry data in Japan.

OBJECTIVE

Differences in hospital case-mix have not been adequately accounted for in hospital volume and patient outcome studies in Japan. We aimed to examine whether differences may exist by investigating the distribution of patients' stage and age across designated cancer treatment hospitals of varying patient volume across Japan.

METHODS

We analyzed data of gastric, breast, colorectal, lung and liver cancer patients who were included in the national database of hospital-based cancer registries between 2008 and 2011. We investigated the association between hospital volume, cancer stage and patient age. Hospitals were classified into five groups according to patient volume.

RESULTS

In total, 676 713 patients met the inclusion criteria. The proportion of patients with early-stage (tumor-node-metastasis Stage 0 or I) cancer was higher among high-volume hospitals for all cancer types except small cell lung cancer. The proportion of older patients (age >75 years) was smaller among high-volume hospitals for all cancer types. The difference in the proportion of patients with early-stage cancers between very low-volume and very high-volume hospitals was greatest for non-small cell lung cancer (26.5% for very low and 43.5% for very high). This difference for the proportion of older patients was also greatest for non-small cell lung cancer (48.9% for very low and 30.3% for very high).

CONCLUSIONS

We showed that the proportions of early-stage cancer patients and younger patients are greater in higher-volume hospitals compared with lower-volume hospitals in Japan. Researchers conducting volume-outcome studies and policymakers analyzing hospital performance should be cautious when making interhospital comparisons.