Oral Embryonal Rhabdomyosarcoma and Its Management: A Rare Enigmatic Pediatric Case Report with Immunohistochemistry.

Aim and background: Malignant tumors are rarely seen in children, of which lymphomas and sarcomas like rhabdomyosarcoma and Ewing sarcoma prevail. Histopathologically, these lesions show numerous round cells, which make it difficult to differentiate between one another. Molecular analysis such as immunohistochemistry has proved to be beneficial and cost-effective. The current report aims to highlight an enigmatic case of embryonal rhabdomyosarcoma (ERMS), emphasizing the role of immunohistochemistry. Case description: A 3-year-old female patient presented to the dental outpatient department with a chief complaint of a progressively enlarging, diffuse swelling over the left cheek region, persisting for the past 2 weeks. Radiographic examination revealed a poorly defined radiopacity involving the maxillary sinus, leading to a provisional diagnosis of odontogenic myxoma. However, tru-cut biopsy from the lesion demonstrated undifferentiated small round to oval cells with occasional strap-like cells and an absence of odontogenic islands, contradicting the initial impression. Subsequent immunohistochemical analysis revealed cytoplasmic desmin positivity, a high Ki-67 labeling index, and negativity for S-100 and CK-19. Based on the immunohistochemical findings, a definitive diagnosis of ERMS was rendered. The patient underwent chemotherapy, and posttreatment evaluation with positron emission tomography and computed tomography (PET-CT) demonstrated marked tumor regression. Conclusion: This case report highlights the crucial importance of using tru-cut biopsy along with immunohistochemical analysis to obtain an accurate and timely diagnosis of ERMS, which facilitates the early start of appropriate targeted treatment. Clinical significance: The resolution of diagnostic challenges in ERMS hinges on the use of meticulous biopsy technique coupled with advanced immunohistochemical analysis.