Role of age and tumour stage in the temporal pattern of ‘cure’ from stomach cancer: A population-based study in Osaka, Japan

Abstract

Objectives: To evaluate progress in stomach cancer care in Japan since 1975. Design: Population-based study of data extracted from the Osaka Cancer Registry. Setting: Population-based cancer registry in the area of Osaka Prefecture. Participants: All 66,032 cases diagnosed with a stomach cancer in Osaka Prefecture, Japan between 1975 and 2000 and registered in the Osaka Cancer Registry. Main outcome measures: ‘Cure’ fraction and median survival time for ‘uncured’ patients were estimated with multivariable mixture ‘cure’ model. The role played by age and stage at diagnosis on the changes in ‘cure’ parameters between 1975 and 2000 was evaluated. Missing stage was handled by multiple imputation approach. Results: More than 50% of the patients diagnosed with a stomach cancer in 1996–2000 were estimated ‘cured’ from their cancer, corresponding to a 20% increase since 1975–1980. Median survival time for ‘uncured’ patients however remained unchanged at about 8 months. ‘Cure’ fraction was over 85% for localised tumours and 30% for regional tumours, but stayed as low as 2.5% for distant metastatic cancers. Improvement was underestimated by about 10% because of ageing of cancer patients. Changes in stage distribution explained up to 40% of the increase in ‘cure’ fraction among men and up to 13% in women. Overdiagnosis was unlikely to play any role in these patterns. Conclusions: ‘Cure’ fraction from stomach cancer dramatically increased in Osaka, Japan since 1975, partly because of earlier stage at diagnosis, but mostly due to improvement in treatment of stomach cancer patients. This study, based on a leading country in term of stomach cancer management, provides insightful results for other countries in which ‘cure’ fraction is usually much lower.