Polymyositis, dermatomyositis and malignancy: a further intriguing link

Area of Science:

• Neurology
• Oncology
• Immunology

Background:

• The association between malignancy and autoimmune myositis is well-established by epidemiological studies.
• The temporal relationship between cancer and myositis varies, with cancer preceding, coinciding with, or following myositis diagnosis.
• Molecular mechanisms linking cancer and myositis remain unclear, though antigenic similarities between myoblasts and cancer cells are proposed.

Purpose of the Study:

• To identify shared histopathologic features between cancer and autoimmune myositis.
• To investigate early myopathic signs in cancer patients without myositis.
• To explore the hypothesis of tumor-induced myopathy triggering autoimmune myositis.

Main Methods:

• Screening of muscle biopsies from patients with polymyositis, dermatomyositis, cancer-associated myositis, and cancer without myositis.
• Histopathologic analysis focusing on muscle fiber characteristics and protein expression.
• Comparison of features across different patient groups.

Main Results:

• Muscle biopsies from myositis patients, particularly those with cancer-associated myositis, showed specific histopathologic features.
• Cancer patients at disease onset exhibited early myopathy signs, including internally nucleated and regenerating myofibers.
• A significant proportion of these regenerating myofibers expressed the neural cell adhesion molecule.

Conclusions:

• Early myopathic changes, including neural cell adhesion molecule expression, are observed in cancer patients.
• A subpopulation of genetically predisposed individuals may develop autoimmune myositis secondary to subclinical tumor-induced myopathy.
• This suggests a potential pathway linking cancer and autoimmune myositis through an immune-mediated response to tumor-associated muscle damage.