Polymyositis, dermatomyositis and malignancy: a further intriguing link

The association between malignancy and autoimmune myositis has been largely described and confirmed by numerous epidemiological studies. The temporal relationship between the two pathologic conditions can vary: malignancy may occur before, at the same time or following the diagnosis of myositis. Beside these observations, the molecular mechanisms underlying this association are still unknown, even though it has been demonstrated a possible antigenic similarity between regenerating myoblasts and some cancer cell populations. To better identify peculiar histopathologic features common to cancer and myositis, we screened muscle biopsies from patients affected with polymyositis, dermatomyositis, myositis in association to cancer, and from patients affected with newly diagnosed cancer, but without myositis. Similarly to the histopatologic features that were observed in the muscle from myositis patients, especially in those with cancer associated myositis, in patients affected with malignancy at the clinical onset of disease we observed early sign of myopathy, characterized by internally nucleated and regenerating myofibers, most of them expressing the neural cell adhesion molecule. The hypothesis that in a particular subset of individuals genetically predisposed to autoimmunity, an initial subclinical tumor-induced myopathy may result in an autoimmune myositis, represents a further intriguing link behind the association of these two conditions.

Subclinical myopathy in patients affected with newly diagnosed colorectal cancer at clinical onset of disease: evidence from skeletal muscle biopsies

OBJECTIVE

To evaluate skeletal muscle biopsy from asymptomatic patients affected with newly diagnosed colorectal cancer and to identify pathological features which may be indicative of tumor-associated muscle disorders, potentially leading to cachexia.

METHODS

Patients affected with newly diagnosed colorectal cancer at clinical onset of disease underwent biopsy of the rectus abdominis muscle during elective laparoscopic tumor resection, before chemotherapeutic treatment. Morphometric analyses, ATPase histochemistry and immunohistochemical studies using antibodies directed to N-CAM and to MHC-emb, two sound makers of muscle denervation and injury-induced muscle regeneration, were performed on intraoperative muscle biopsies from ten patients. Muscle biopsies from rectus abdominis of seven subjects affected with non-neoplastic condition, which underwent laparoscopic surgery, were used as controls.

RESULTS

In patients' biopsies, we observed a surprisingly high percentage of myofibers with internalized or central nuclei compared to controls (9.15 +/- 8.9 versus 0.6 +/- 0.9, p<0.0003). In addition, in the 30% of patients, small myofibers expressing the MHC-emb have been identified (0.4 +/- 0.5 positive fibers/mm(2)), while in 50% of patients, larger fibers positive for N-CAM have also been detected (0.7 +/- 1.1 positive fibers/mm(2)), suggesting that investigated muscle biopsies exhibit other evidence of muscle fiber injury/regeneration and/or denervation. Among the 10,000 analysed myofibers in control biopsies, no MHC-emb and N-CAM-positive muscle fibers have been detected. Thus, patients affected with newly diagnosed colorectal cancer at clinical onset of disease display early signs of a subclinical myopathy.

DISCUSSION

Factors and mechanisms of this cancer-associated myopathy are yet unknown. The facts that the great majority of the abnormally nucleated myofibers are of the fast type and that regenerating myofibers are present, suggest a myogenic response to the colorectal cancer and not to the laparoscopic modalities of the biopsy harvesting. Follow-up of the patients will elucidate the clinical relevance of our observation, and further studies investigating the molecular mechanism underlying this early cancer-associated myopathy will hopefully provide some pathogenetic clues leading to the identification of potential specific targets for therapeutic intervention to prevent tumor cachexia.