Head and Neck Rhabdomyosarcoma in Pediatric Patients: An International Collaborative Study.

Background: Rhabdomyosarcoma (RMS), a rare malignant tumor, frequently affects pediatric patients, with 35%-40% occurring in the head and neck. This study analyzes the clinicopathologic profile of pediatric head and neck rhabdomyosarcomas from Brazil, Guatemala, Mexico, and South Africa.

Methods: We reviewed 44 cases from 10 Oral and Maxillofacial Pathology services, conducting immunohistochemical analyses of desmin, myogenin, Myo-D1, and Ki67, with quantification via QuPath software. Cases with ≥ 50% myogenin expression were tested for fusion status using AP2β, NOS-1, and HMGA2. Statistical analyses included the Kruskal-Wallis test for age and marker expression comparisons, Fisher's exact test for categorical variables, Spearman's rank correlation for marker relationships, and multinomial logistic regression to assess fusion status likelihood.

Results: Cases were predominantly from Brazil (40.9%), followed by South Africa (27.3%), Guatemala (22.7%), and Mexico (9.1%). Two-thirds of patients were diagnosed in their first decade with no gender predilection. Nonparameningeal sites (45.5%) were more affected than parameningeal (40.9%) and orbital sites. Microscopically, embryonal RMS (77.3%) was most common, followed by alveolar (18.2%) and spindle cell (2.3%) tumors. Immunohistochemistry revealed positivity for myogenic markers, with significant differences in myogenin expression between embryonal and alveolar RMS variants (p < 0.05). Fusion status prediction identified two potential fusion-positive alveolar RMS cases, while all embryonal RMS and one alveolar RMS case appeared fusion-negative. Significant correlation with positive fusion status was found only between AP2β and NOS1 (p < 0.05).

Conclusion: Although there are slight clinical-demographic variations among pediatric head and neck rhabdomyosarcomas in these regions, identifying fusion status through immunohistochemistry remains a diagnostic challenge.