Why is colon cancer survival improving by time? A nationwide survival analysis spanning 35 years

There is limited information present to explain temporal improvements in colon cancer survival. This nationwide study investigates the temporal changes in survival over a 35-year period (1970-2004) in Iceland and uses incidence, mortality, surgery rate, stage distribution, lymph node yield, tumor location and histological type to find explanations for these changes. Patients diagnosed with colon cancer in Iceland 1970-2004 were identified (n=1962). All histopathology was reassessed. Proportions, age-standardized incidence and mortality, relative, cancer-specific and overall survival and conditional survival were calculated. When comparing first and last diagnostic periods (1970-1978 and 1997-2004), 5-year relative survival improved by 12% for men and 9% for women. At the same time surgery rate increased by 12% and the proportion of stage I increased by 9%. Stage-stratified, improved 5-year relative survival was mainly observed in stages II and III and coincided with higher lymph node yields, proportional reduction of stage II cancers and proportional increase of stage III cancers, indicating stage migration between these stages. Improvement in 1-year survival was mainly observed in stages III and IV. Five-year survival improvement for patients living beyond 1 year was minimum to none. There were no changes in histology that coincided with neither increased incidence nor possibly influencing improved survival. Concluding, as a novel finding, 1-year mortality, which previously has been identified as an important variable in explaining international survival differences, is in this study identified as also being important in explaining temporal improvements in colon cancer survival in Iceland. What's new? Icelanders are surviving colon cancer more often than they used to; between 1970 and 2004, the survival rate increased by 12% for men and 9% for women. What changed? For this article, the authors collected data on factors like incidence, mortality, surgery rate, stage, and histological type to pinpoint how the improvement came about. The biggest gains, they found, occurred within the first year after diagnosis; 1-year survival improved, particularly for patients with later stage tumors, while the 5-year survival rate of those surviving beyond 1 year did not change.