Patients with rheumatic diseases have an increased risk overall for cancer compared to the normal population. This is most pronounced for patients with SLE, but patients with rheumatoid arthritis have also a significantly increased risk. Unpublished data from Sweden also indicate that such an association exist for patients with Morbus Bechterew as well as patients with psoriatic arthritis.
However, the increased cancer risks are not general phenomenon for cancer as such. There are distinct differences in the patterns of cancer occurrence compared to the general population. Smoking related cancers, especially lung cancer, occur in excess for both rheumatoid arthritis and SLE patients as opposed to cancers of the gastrointestinal tract (especially colorectal cancer) which are inversely associated with all four disease entities mentioned above, possibly due to the pharmacotherapy these patients are exposed to.
Hematopoetic cancers (lymphomas and leukemias) also occur more than that expected in patients with rheumatic diseases. In the case of SLE and rheumatoid arthritis these excess risks are especially prominent for lymphomas, but there is also a somewhat less pronounced increased risk for leukemias. This increased risk can probably, to some extent, be explained by immunosuppressive therapy. However, the increased risk for lymphomas in a Swedish setting was already present in these patient groups before the introduction of such therapies during the 1970’s. Moreover, the risk estimates for lymphomas have not been altered after the introduction of such therapies. The absence of an impact of immunosuppressives can, perhaps, to some extent be due to a substantially increased absolute risk of lymphomas in the general population, which means that the cumulative incidence of lymphomas among patients with rheumatic disease is presently higher than it was 20 years ago.
High disease activity in patients with rheumatic arthritis seems to be associated with an even more pronounced risk for lymphomas. There are indications that anti-inflammatory therapy have a protective effect, although better data is needed before such an association can be firmly established.
In conclusion, rheumatic diseases are associated with increased risk for cancer. Hematopoetic cancers are, however, the only malignancy where a causal association has been established.
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