Skeletal muscle infiltration in carcinoma is a rare entity. Intramyofiber skeletal muscle invasion is the rarest type of muscle infiltration. Here we present one such case of intramyofiber skeletal muscle invasion in a case of breast carcinoma.
Keywords: Breast carcinoma, intramyofiber invasion, skeletal muscle invasion
|How to cite this article:
Dey S, Chatterjee U, Datta C. Intramyofiber skeletal muscle invasion: An unusual pattern of muscle infiltration in breast cancer. Indian J Pathol Microbiol 2022;65:478-9
|How to cite this URL:
Dey S, Chatterjee U, Datta C. Intramyofiber skeletal muscle invasion: An unusual pattern of muscle infiltration in breast cancer. Indian J Pathol Microbiol [serial online] 2022 [cited 2022 May 3];65:478-9. Available from: https://www.ijpmonline.org/text.asp?2022/65/2/478/343186
Muscle invasion in breast cancer is now rare because of advent of neoadjuvant chemotherapy. However when present, it is often associated with higher stage and poor prognosis. Muscle infiltration by cancer is of two types: either by direct invasion or by metastasis. The usual morphological patterns are invariably infiltration of the connective tissue that forms the perimysium and endomysium between the muscle bundles and fibers. This needs to be differentiated from myositis. Patients with myositis usually present with selective proximal muscle weakness and elevated serum levels of creatinine kinase (CK), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), and alanine aminotransferase (ALT). Recent The European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification divided myositis into five groups; out of which polymyositis is frequently associated with internal malignancies. Another rare pattern of muscle infiltration is intramyofiber invasion where tumor cells break the sarcoplasmic membrane and grow along the muscle fiber sarcoplasm without disrupting the architecture. One such case of intramyofiber skeletal muscle invasion in a case of breast carcinoma is illustrated here.
A 50-year-old woman presented with a right-sided breast lump measuring 5 cm across and with axillary nodes. She underwent a modified radical mastectomy and the sections showed histological features of invasive breast carcinoma No special type (NST), modified Bloom–Richardson grade II with lymph nodal involvement. In addition, sections were taken from the axillary pad of fat that contained pectoralis minor muscle fibers. Longitudinal and transverse sections showed intrasarcoplasmic muscle infiltration by tumor cells maintaining the shape of the muscle fibers. In transverse sections 12–16 tumor cell nuclei per muscle fiber were identified and many of them had a thin rim of sarcoplasm around the periphery. This thin rim of sarcoplasm was brought out better on desmin stain. The tumor nuclei showed positivity for Estrogen receptor (ER), progesterone receptor (PR), and were negative for Her2Neu, in keeping with the primary tumor [Figure 1]. There was no evidence of lympho-mononuclear cell infiltration at endomysial or perimysial location to indicate myositis. Serum CK, LDH, and AST levels were within normal limits on the seventh postoperative day. There were no associated symptoms of proximal muscle weakness, skin rash, or dysphagia.
|Figure 1: (a) Scan power showing cross-section of muscle with dark stained tumor cells within some myofibers (H and E,40x). (b) Longitudinal section of muscle showing similar tumor cells within myofiber. (c) Low-power view showing rim of sarcoplasm around the tumor cells; inset shows high power of same. (d) High-power view showing similar tumor cells, peripheral normal sarcoplasm (400x). (e) Low power showing desmin positive muscle fibers and desmin negative tumor cells (100x); inset shows high-power view of desmin positive sarcoplasm (400x). (f) Low-power view showing ER-positive tumor nuclei (100x); inset shows high power of same (400x)|
Intramyofiber muscle invasion by carcinoma is a rare phenomenon and only two cases have been reported so far., Intramyofiber muscle infiltration has occasionally been reported in cases of Ewings, Non-Hodgkin’s lymphoma (NHL), and leukemia, Skeletal muscle invasion itself is uncommon possibly due to a hostile microenvironment created by muscle pH and mechanical tumor destruction by motion. The exact mechanism of intramyofiber invasion is not clear as tumor cells need to break through the sarcolemma to grow along the myofiber. Sarcolemma along with external lamina is very resistant to enzymatic, mechanical, and chemical damage due to the supporting proteoglycans maintaining the stability.
Recently, Magnetic resonance (MR) scans have proven to be useful in detecting muscle invasion and metastasis but even on MR scan, the features of muscle invasion are not very clear. For these reasons, muscle infiltration in carcinoma is often under-reported and missed. From a diagnostic point of view, intramyofiber infiltration must be recognized as a pattern of muscle invasion. On low power, it can easily be missed as it maintains the shape of the muscle fibers. The prognostic significance of this type of infiltration pattern is unknown because of the small number of reported cases.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
Source of Support: None, Conflict of Interest: None