[Malignancy-associated myositis]

Inflammatory myopathies, also referred to as myositis, are a heterogeneous group of chronic inflammatory muscle diseases characterized by various clinical features and histological changes; in addition, patient with these disease exhibit positivity for autoantibodies as well as progressive inflammatory muscle damage and experienced weakness. Although it has been well known for a century that myositis, particularly dermatomyositis, can be associated with malignancy, it was not until recently that the result of robust epidemiological studies confirmed this association. Malignancy-associated myositis differs from primary myositis in many aspects. Prognosis and life expectancy for patients are determined on the basis of the underlying malignancy. Therefore, patient-specific examinations to detect an underlying cancer are important for the management of these patients. Recently, a novel myositis-specific autoantibody (anti-p155 or p155/p140 antibody) was identified in malignancy-associated myositis. The discovery of this autoantibody is important not only for an early diagnosis of adult-onset myositis patients with a higher risk of malignancy but also for a better understanding of the pathogenesis of paraneoplastic myositis. In addition, it has also been recently found that both regenerating cells in myositis muscles and several cancers known to be associated with myositis express high levels of myositis-specific autoantigens. Therefore, a model of paraneoplasia focusing on the expression of common autoantigens expression and immuno-targeting between cancer and muscle tissues in myositis has been proposed. In this review, we aim to describe epidemiological evidence for an association between myositis and malignancy, and to describe the clinical features of malignancy-associated myositis. We also aim to focus on a recently proposed model to understand the development of malignancy-associated myositis.