MYOD1 (L122R) mutations are associated with spindle cell and sclerosing rhabdomyosarcomas with aggressive clinical outcomes

Bharat Rekhi,Pawan Upadhyay,Manoj P Ramteke,Amit Dutt

doi:10.1038/modpathol.2016.144

Abstract

Recurrent mutations in the myogenic transcription factor MYOD1 and PIK3CA were initially described in a subset of embryonal rhabdomyosarcomas. Recently, two independent studies demonstrated presence of MYODI (L122R) mutations as the basis to re-classify a spindle cell rhabdomyosarcoma, along with a sclerosing rhabdomyosarcoma, distinct from an embryonal rhabdomyosarcoma. We analyzed a much larger cohort of 49 primary rhabdomyosarcoma tumor samples of various subtypes, collected over a period of 9 years, for the presence of MYOD1 (L122R), PIK3CA (H1047), and PIK3CA (E542/E545) mutations, along with immunohistochemical analysis of desmin, myogenin, and MYOD1. Although activating PIK3CA mutations were absent across the sample set analyzed, we report 20% MYOD1 (L122R) mutation in rhabdomyosarcomas, found exclusively in 10 of 21 spindle cell and sclerosing rhabdomyosarcomas, occurring mostly in the head and neck region along with extremity sites (64%), than the paratesticular and intra-abdominal sites. Furthermore, while all 10 MYOD1 mutant spindle cell and sclerosing rhabdomyosarcoma samples showed diffuse and strong MYOD1 immunoexpression, 7 of 31 samples of rhabdomyosarcoma with wild-type MYOD1 were negative for MYOD1 expression. Clinically, a striking correlation was found between MYOD1 mutation and the clinical outcomes available for 15 of 21 cases: 5 of 7 patients with spindle cell and sclerosing rhabdomyosarcomas, harboring MYOD1 mutation, were alive-with-disease and 2 of 8 patients with spindle cell and sclerosing rhabdomyosarcomas, with mutant MYOD1, were free-of-disease. Taken together, we present the first report of MYOD1 (L122R) mutation in the largest cohort of 49 rhabdomyosarcomas reported so far, that are associated with a relatively aggressive clinical course. Moreover, consistent with the earlier two studies, this study further reinforces a relationship between spindle cell and the sclerosing rhabdomyosarcoma—now recognized as a single subtype, distinct from an embryonal rhabdomyosarcoma.

Highlights

Various investigators have unraveled genetic events underlying cases of spindle cell and sclerosing RMS
Kohsaka et al[14] initially described a recurrent MYOD1 (L122R) mutation defining a clinical subset of embryonal RMSs associated with PI3K-AKT pathway mutations
We present a systematic analysis of activating mutations in MYOD1 and PIK3CA along with the expression of desmin, MYOD1, and myogenin in a much larger cohort of 49 primary samples of RMS collected over a period of 9 years: comprising of 21 spindle cell and sclerosing RMSs, 10 embryonal RMS,s 17 alveolar RMSs, and a single case of a pleomorphic RMS

Summary

Introduction

Various investigators have unraveled genetic events underlying cases of spindle cell and sclerosing RMS. Kohsaka et al[14] initially described a recurrent MYOD1 (L122R) mutation defining a clinical subset of embryonal RMSs associated with PI3K-AKT pathway mutations. MYOD1 in adult spindle cell RMSs,[15] and pediatric and adult sclerosing RMSs16 reinforcing a relationship between these two morphological variants of a RMS. We present a systematic analysis of activating mutations in MYOD1 and PIK3CA along with the expression of desmin, MYOD1, and myogenin in a much larger cohort of 49 primary samples of RMS collected over a period of 9 years: comprising of 21 spindle cell and sclerosing RMSs, 10 embryonal RMS,s 17 alveolar RMSs, and a single case of a pleomorphic RMS

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Results

Conclusion