A comparison of population-based data from six wealthy countries has demonstrated that differences in stage at diagnosis explain some but not all of the international variation in overall lung cancer survival.

“Wide disparities in stage-specific survival exist, suggesting that other factors are also important, such as differences in treatment,” concluded Dr. Sarah Walters, of the Cancer Research UK Cancer Survival Group at the London School of Hygiene and Tropical Medicine (London, United Kingdom), and colleagues, in the BMJ journal Thorax.

According to an accompanying statement from BMJ, stage at diagnosis has often been suggested as one of the primary reasons why lung cancer survival is low in certain countries, such as the United Kingdom: Patients don’t see their doctors until it’s too late for treatment to be effective. To explore this theory, Walters and fellow researchers obtained population-based data that had been routinely collected on all 57,352 persons aged 15 to 99 years who had been diagnosed with lung cancer in the 2004–2007 period and registered in regional and national cancer registries in Australia, Canada, Denmark, Norway, Sweden, and the United Kingdom.

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Average age at diagnosis was 70 years. The United Kingdom had the highest proportion of patients for whom data on stage were missing.

The investigators used the information to estimate net survival at 1 year and excess hazard up to 18 months after diagnosis. Their analysis revealed that age-standardized 1-year net survival from non-small cell lung cancer (NSCLC), which accounts for the majority of all lung cancers, ranged from 30% (United Kingdom) to 46% (Sweden). Survival was also high in Australia and Canada (both 42%), and intermediate in Norway (39%) and Denmark (34%).

Although patients in the United Kingdom and Denmark had lower survival compared with patients elsewhere, partly because of a more adverse stage distribution, wide international differences also existed in stage-specific survival. Net survival from TNM stage 1 NSCLC was 16% lower in the United Kingdom than in Sweden, and net survival for TNM stage IV disease was 10% lower. Walters’ team found similar patterns for small cell lung cancer. 

Differences in the pattern of disease, in delays in diagnosis, or in the testing for each stage may account for some of the variation in survival rates. The authors noted that low stage-specific survival in the United Kingdom could conceivably arise in part because of suboptimal staging, leading to inappropriate treatment and greater mortality. Other factors such as differences in quality of and access to treatment were also deemed likely to play a part.