[Clinicopathological features and prognosis of pediatric alveolar rhabdomyosarcoma].

Objective: To investigate the clinicopathological features, diagnosis, differential diagnosis, treatment and prognosis of pediatric alveolar rhabdomyosarcoma (ARMS). Methods: The clinical and pathological data of 25 pediatric ARMS from 2008 to 2018 in Children's Hospital of Fudan University were collected. This histomorphology was assessed, and FOXO1 gene rearrangement was detected with FISH. The treatment details and outcome were analyzed. Results: There were 13 males and 12 females, with ages range from 19 days to 14 years (median 6 years, mean 6.2 years). The ARMS were located in the limbs (13 cases), head and neck (4 cases), trunk (3 cases), abdominal cavity (3 cases), scrotum (1 case) and perianal region (1 case). The ARMS were classified histologically as classic group (18 cases), solid group (5 cases) and embryonic-alveolar mixed group (2 cases). The typical pathological characteristics were small dark round cells arranged in solid, glandular and papillary patterns. The tumor cells expressed ALK (D5F3) (21/25, 84.0%), muscle origin DES (23/25, 92.0%), myogenin (22/25, 88.0%), MYOD1 (19/25, 76.0%), and in some cases they also expressed neurogenic marker Syn (6/25, 24.0%). FOXO1 gene rearrangement was detected by FISH in 24/25 cases (96.0%). Conclusion: Pediatric ARMS is rare and has unique clinicopathological characteristics, and needs to be differentiated from other common small round cell malignancies in children. ALK, DES, myogenin, MYOD1 immunohistochemistry and FOXO1 gene rearrangement are valuable aid in the diagnosis of ARMS.