Regenerating skeletal muscles in surgical scar endometriosis are not 'atypical'

Dear Editor, We read with great interest the Letter to Editor titled ”Atypical myocytes: A quirky impersonator in surgical scar endometriosis!”[1] The authors document aptly that regenerating myocytes can mimic a neoplasm. We, too, have seen four cases of abdominal wall endometriosis with regenerating skeletal muscle and agree with the authors that lack of awareness of the morphology of regenerating myocytes could potentially mislead unwary pathologists into suspecting a neoplastic pathology. We commend the authors’ insight for making the correct diagnosis. However, we take issue with the use of the word “atypical” in the title and in the letter itself. The word “atypical” is defined as the “state of being not typical or normal, and in medicine, connotes an abnormality in cells in tissue,” as per the National Cancer Institutes Dictionary of Cancer Terms.[2] In pathology, the word atypia usually implies precancer or an abnormal morphology that mimics cancer. However, regenerating myocytes, though showing bizarre or hyperchromatic nuclei at times, are in reality perfectly normal for their stage of differentiation and hence cannot be called atypical. Further, the letter does not cite any relevant articles. Readers would benefit from reading an article by Colella et al.[3] who described this morphology for the first time in 2010 in four cases of post-cesarean scar endometriosis. They demonstrated that these cells represented maturing myoblasts, with the least differentiated ones being closest to the endometriotic foci and the most mature myoblasts being more peripherally placed, based on their immunohistochemical profile, which recapitulated that of regenerating skeletal muscle. They found that the less differentiated cells expressed vimentin, desmin, S100, CD56, myoD1, and myogenin, but not myoglobin or p21. Intermediately differentiated cells showed a progressive loss of vimentin, CD56, and myoD1 but were positive for desmin, S100, myogenin, myoglobin, and p21. Terminally differentiated cells expressed only desmin and myoglobin. Based on these findings, they postulated that muscle cells were stimulated by growth factors or other signals from the cycling endometriotic foci. More recently, Mirza et al.[4] reported a similar case where they demonstrated the presence of intracytoplasmic myofibrils in these cells by electron microscopy, confirming that they represented myocytes. To sum up, pathologists must recognize impersonators of malignant tumors but must use etymologically correct terms. As Humpty Dumpty states in Through the Looking-glass and What Alice Found There, “When I use a word, it means just what I choose it to mean — neither more nor less.”[5] Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.