Cancer and myositis: new insights into an old association.

PURPOSE OF REVIEW: The association between the idiopathic inflammatory myopathies and the development of malignancy has been appreciated for nearly a century, but its meaning and significance have remained unclear. Significant advances in our understanding of the epidemiology and pathophysiology of this association have recently been made. This review will describe the major epidemiological evidence linking inflammatory myopathies with cancer, and will use this evidence to highlight a recently proposed model for the development of cancer-associated myositis.

RECENT FINDINGS: The temporal relationship between the development of cancer and myositis is reminiscent of that seen in neurological paraneoplastic disorders, in which antigens targeted for an immune response are expressed at high levels in the inciting tumor and the affected neuronal tissue. It has also recently been observed that regenerating cells in myositis muscle, but not its normal counterpart, express high levels of myositis-specific autoantigens. These same antigens are expressed at high levels in several cancers known to be associated with the development of myositis, but not in corresponding normal tissue.

SUMMARY: These observations suggest a model of paraneoplasia focusing on common autoantigen expression and immune targeting between cancer tissues and muscle tissue in myositis.