Rheumatoid factor isotypes and cancer prognosis.

The relationship between rheumatoid factor (RF) and cancer was studied during a long-term health survey done in the Reykjavik area of Iceland since 1967. A total of 16,299 blood samples from 13,858 persons attending this health survey between 1974 and 1983 were screened for the presence of RF. In 1987, RF-positive participants in this study (n = 270) and matched RF-negative control subjects (n = 223) were evaluated for incidence and prognosis of cancer with information obtained from the comprehensive Icelandic Cancer Registry. The average observation time for this cohort was 9.3 years. Participants with raised immunoglobulin A RF in their original blood sample showed an increased risk of having cancer compared with both other members of the cohort and the national cancer incidence. Their total mortality was also higher during the study period. By contrast, patients with cancer and elevated immunoglobulin M RF before the diagnosis of cancer were more likely to survive than those who were immunoglobulin M RF negative. Cancer incidence in the RF-negative control group was not different from the expected national incidence of cancer in Iceland for that age group. It is suggested that elevation of immunoglobulin A RF is an adverse phenomenon in relation to cancer; elevation of immunoglobulin M RF is associated with a favorable prognosis.