To analyze whether fibromyalgia (FM) and FM-like symptoms are related to an increased incidence of cancer.
We identified 1361 patients referred on suspicion of FM in the period 1984-99 from hospital records. Following the American College of Rheumatology (ACR) criteria, patients were divided into subgroups with and without confirmed FM. The cohort was followed to the end of 1999 and linked to the files of the Danish Cancer Register. Site-specific standardized incidence ratios (SIR) were calculated.
We found no association between FM and cancer in 1132 female patients with confirmed FM at our institution (SIR 1.2, 95% CI 0.8-1.8). In 106 women referred for muscle pain and/or tenderness who did not meet the criteria for FM, an increased overall SIR was observed (SIR 2.5, 95% CI 1.2-4.6), with increased risk for breast cancer (SIR 4.8, 95% CI 1.6-11.3) and lymphatic and hematological cancers (SIR 10.6, 95% CI 1.2-38.2). There were 4 lung cancers in 84 men with confirmed FM (SIR 12.6, 95% CI 3.4-32.4).
Neither confirmed FM nor those without confirmed FM predicted cancer. An increased risk of breast cancer was found among those who did not meet the ACR criteria for FM. These patients should be investigated if they develop any new or warning symptoms of malignancy, and treating physicians should be vigilant with screening procedures such as mammography.