Influence of inflammatory polyarthritis on cancer incidence and survival

Patients with rheumatoid arthritis (RA), a chronic inflammatory autoimmune disease, have a high risk of death from disease - at least double the risk of the general population, studies overwhelmingly show. Evidence has been less clear on whether RA patients are exceptionally vulnerable to dying from cancer.

The first study to investigate whether patients with RA who develop cancer have a decreased rate of survival, featured in the March 2007 issue of Arthritis & Rheumatism, also examined the impact of rheumatic disease on overall cancer incidence. Conducted by a team of researchers in the United Kingdom, it focused on 2,105 patients with recent onset inflammatory polyarthritis (IP). Over time, a large proportion of new-onset IP cases evolve into RA, meeting the diagnostic criteria of the American College of Rheumatology.

Researchers followed the IP patients over a 10-year period to detect the occurrence of cancer. Among the group, they identified 123 cases of cancer for analysis. These cases included bone, lung, breast, prostate, urinary, colon, and brain cancers; cancers of the digestive, respiratory, and central nervous systems; cancers of the blood cells and cancerous tumors; but excluding non-melanotic skin cancers. Then, they compared these rates with the rates of cancer in the general population from the same geographic area, Norfolk, adjusting for difference in age and sex. Overall, the incidence of cancer was not increased in the IP subjects compared with the general population. However, the risk of blood cell cancers was increased among the IP sample, a finding researchers expected given the association between RA and lymphoma.

The study also compared the number of deaths in patients with cancer and inflammatory arthritis with that of cancer patients without a history of inflammatory arthritis. The finding was striking: a 40 percent increase in mortality in patients who suffered both IP, or RA, and cancer.

"The results of this study demonstrated that 5-year cancer survival in patients with IP is substantially reduced in comparison with that in the general population, even after adjusting for differences in age, sex, and cancer site, whereas the overall cancer incidence does not seem to be increased," observes Alan Silman, M.D., an epidemiologist with the University of Manchester and the study's leading researcher. Whether targeted cancer therapies could improve the survival rate for RA patients remains a subject for further research.