[Detection of MYOD1-mutation of rhabdomyosarcoma and its clinicopathological characteristics]

Objective: To investigate a new method for rapid detection of the MYOD1 L122R mutation and to analyze the clinical and pathological characteristics of mutation-positive rhabdomyosarcoma. Methods: A MYOD1 mutation detection kit was developed using allele-specific Taqman fluorescence probe technology. A total of 80 rhabdomyosarcoma samples diagnosed at Beijing Children's Hospital, Capital Medical University from June 2022 to June 2023 were collected for testing. The detection sensitivity, specificity, and consistency rate of the kit were compared with those of the gold standard Sanger sequencing. The demographic, histopathological, and molecular genetic characteristics of patients with MYOD1 mutations were analyzed. Results: Among the 80 rhabdomyosarcoma cases, there were 46 males and 34 females, with an age of onset ranging from 0 to 16 years [mean (6.0±4.4) years], including 32 embryonal rhabdomyosarcoma, 18 alveolar rhabdomyosarcoma, and 30 spindle cell/sclerosing rhabdomyosarcoma. The new kit screened a total of 11 mutations, of which 10 were spindle cell/sclerosing rhabdomyosarcoma and one was embryonal rhabdomyosarcoma. Patients with MYOD1 mutations were typically older (four cases over 10 years old) but could also occur in young children (the youngest being 3-year and 2-month-old). The primary sites were the head and neck region in eight cases, limbs in two cases, and pelvic cavity in one case. Among the six patients with available staging information at initial diagnosis, one was classified as stage 2 and five were stage 3, all of which were intermediate risk. Among the 11 mutation patients, six had recurrence and metastasis, with three deaths; the remaining patients had not shown tumor progression until last follow-up. Compared with the wild type group, the expression level of MYOD1 in mutation patients increased significantly (χ²=10.66, P=0.01), while the event-free survival rate (χ²=9.925, P<0.01) and overall survival (χ²=4.53, P=0.03) rate decreased. Compared with Sanger sequencing, the kit achieved 100% sensitivity and specificity. The kit had a minimum mutation content detection limit of 2% and the reaction could be finished within 2 hours. Additionally, this kit might also be used to detect the expression of MYOD1, thereby aiding the diagnosis of rhabdomyosarcoma. Conclusions: The study has established a new method for accurate and rapid detection of MYOD1 mutation in rhabdomyosarcoma, particularly suitable for the formalin-fixed and paraffin-embedded samples in clinical settings. MYOD1 mutations more likely occur in spindle cell/sclerosing rhabdomyosarcoma of the head and neck region in children. Patients with MYOD1 mutations have an extremely poor prognosis, which is independent of clinical staging and grading. MYOD1 mutation detection in rhabdomyosarcoma has significant value for auxiliary diagnosis and prognostic assessment.