SNOWMASS, COLO. — A novel myositis-specific autoantibody shows promise for predicting which patients with idiopathic inflammatory myositis are at increased cancer risk, Dr. Robert L. Wortmann said at a symposium sponsored by the American College of Rheumatology.
“It looks like we may have found a marker that's more predictive of cancer than any marker we've had before,” observed Dr. Wortmann, professor of medicine at Dartmouth-Hitchcock Medical Center, Lebanon, N.H.
Case-control and population-based cohort studies show patients with idiopathic inflammatory myositis are at increased risk of cancer. A serologic test to help identify the subgroup warranting intensive cancer surveillance is needed.
Dr. Wortmann credited Dr. Hector Chinoy of the University of Manchester (England) and coworkers at the University of Pittsburgh with demonstrating the new autoantibody's utility in predicting cancer-associated myositis. The antibody is a doublet directed against a 155-kDa protein and a 140-kDa protein.
The investigators tested for this and a comprehensive array of more conventional myositis-specific autoantibodies in a large cohort comprising 109 white adults with polymyositis, 103 with dermatomyositis, and 70 myositis/connective tissue disease overlap patients with primary diagnoses including systemic sclerosis, mixed connective tissue disease, Sjögren's syndrome, and systemic lupus erythematosus.
Sixteen of the 282 patients had cancer-associated myositis, defined as cancer developing within 3 years of diagnosis of the myositis. Fifteen of the 16 had dermatomyositis and 1 had a connective tissue disease overlap syndrome, confirming reports that cancer risk is greater in dermatomyositis than in polymyositis.
Anti-155/140-kDa antibody was found exclusively in dermatomyositis patients, with a prevalence of 18%. The antibody was present in 8 of 16 patients with cancer-associated myositis, but in only 11 of 266 without it. Seven of eight anti-155/140-kDa antibody-positive patients who developed cancer did so within 1 year of dermatomyositis diagnosis.
A positive anti-155/140-kDa antibody test had 96% specificity, 50% sensitivity, a 42% positive predictive value, and a 97% negative predictive value for cancer-associated myositis.
The combination of a positive anti-155/140-kDa antibody test and a negative result on a routine myositis antibody panel testing for anti-Jo-1, anti-U1-RNP, anti-U3-RNP, anti-PM-Scl, and anti-Ku antibodies detected 15 of 16 cases of cancer-associated myositis. The combination had a sensitivity of 94% and a negative predictive value of 99% (Ann. Rheum. Dis. 2007;66:1345–9).
Testing for anti-155/140-kDa antibody isn't commercially available at present.