Rheumatoid arthritis (RA) alters the risk for developing cancer, indicate US study findings showing both positive and negative associations between the two diseases. “Large longitudinal studies, which collect detailed risk factor and treatment information, are needed to investigate the mechanisms that underlie the associations between RA and specific cancer types,” say Arti Parikh-Patel, from the Public Health Institute in Sacramento, California, and co-workers. The team collated data from statewide patient discharge records and a cancer registry for 1991–2002 and determined age-, gender-, and race-adjusted standardized incidence ratios (SIRs) for expected and actual cancer rates in 84,475 RA patients compared with the overall Californian population. Over 405,540 person-years of follow-up, 5533 cancers were reported in the RA patients, the researchers report in the journal Cancer Causes and Control. Analysis showed that both male and female RA patients had a significantly increased risk for lymphohematopoietic cancer, such as non-Hodgkin’s lymphoma and leukemia (SIR=2.07 and 1.37, respectively), and colorectal cancer (SIR=0.70 and 0.76, respectively) compared with expected rates. In addition, male RA patients had an increased risk for lung (SIR=1.65), liver, (SIR=1.85), and esophageal cancer (SIR=1.78), but a lower risk for prostate cancer (SIR=0.67) than men in the general California population. Women with RA had an increased risk for lung cancer compared with general population (SIR=1.28), but unexpectedly had significantly lower risks for cancers of the breast (SIR=0.63), ovary (SIR=0.63), uterus (SIR=0.530, and cervix (SIR=0.43), and melanoma (SIR=0.63). This novel finding could be due to RA having fewer risk factors for hormone-related diseases such as smoking, diet, obesity, or reproductive history, the researchers suggest. “The lower risks of hormone-related cancers could also be related to endogenous hormone levels, which have also been implicated in RA risk and disease severity,” they add. Hispanic RA patients had a greater risk for leukemia, and cancers of the vagina/vulva (SIR= 2.71), lung (SIR for men and women=1.75 and 1.93, respectively), and liver (SIR=2.70 and 2.65, respectively) compared with the general population. Parikh-Patel et al therefore conclude: “Since no previous research has stratified cancer risk among RA patients by race/ethnicity, further analysis of factors that influence differences in cancer risk across race/ethnic groups is needed.”
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