Reacción a "The Basque Country’s colorectal cancer screening programme was associated with a 50 per cent reduction in mortality from this cause among adults aged 50 to 69"

The study is of a very high standard, but we must not lose sight of the fact that it is an observational study and the evidence it generates must be put into context. In this case, the context is that the effectiveness of colorectal cancer screening has been demonstrated through randomised clinical trials (one of the most reliable sources of evidence for establishing causality). Therefore, although – as the authors note in the discussion – there are factors that may have changed during the study period and which may have contributed to the decline in mortality from colorectal cancer (for example, health behaviours or access to the healthcare system), it is reasonable to assume that screening has made a significant contribution to the decline in colourectal cancer-specific mortality.

The main implication of this study is that it highlights the importance of a public health system with robust policies on cancer prevention and screening. In the case of the Basque Country, the colorectal cancer screening programme has been in place without interruption since 2009, which has helped to generate the benefits reported in this study.