Season may not alter cancer survival in short term

NEW YORK (Reuters Health) - Some studies have found that patients with certain cancers seem to survive longer when they're diagnosed during summer and autumn months, but it now appears that this may be largely due to higher death rates in general during winter months, report UK researchers from King's College London.

Dr. David Robinson and colleagues note in the International Journal of Cancer that none of the previous studies accounted for monthly variations in both short-term survival and for mortality rates in the general population.

To address this, the investigators looked at data on 606,501 men and 580,946 women diagnosed with cancer from 1975 through 2004.

Compared with a winter diagnosis, men and women diagnosed with colorectal or lung cancer during summer had substantially decreased mortality within the first month of diagnosis.

The investigators found similarly decreased mortality among men diagnosed with prostate cancer, and women diagnosed with breast cancer.

However, these short-term survival benefits lessened in analyses that factored in monthly variations in general mortality. In other words, the apparent short-term phenomenon of better summer/autumn survival appears "caused by generally higher mortality in the winter months," Robinson and colleagues explain.

On the other hand, their assessment of long-term survival (over 5 years) showed decreased mortality among men and women diagnosed with lung cancer and women diagnosed with breast cancer during the autumn, as opposed to the summer.

This may indicate a true "seasonally variable protective mechanism," but it might not apply everywhere. Seasonal differences in cancer survivability are likely due to biological factors, patients' expectations of health, health care provisions, as well as fluctuations in general mortality, the team points out. As such, findings from one country may not be generalizable to other countries.

SOURCE: International Journal of Cancer, May 2009.