An Atypical Presentation, Diagnostic Challenges, and Treatment Response of a Malignant Small Round Cell Tumor in the Lumbo-Inguinal Region of an Infant.

Malignant small round cell tumors are a heterogeneous group of aggressive neoplasms characterized by small, round cell morphology. The undifferentiated cells in these tumors exhibit a high nuclear-cytoplasmic ratio, and definitive histologic diagnosis via light microscopy can be extremely challenging. Diagnostic accuracy significantly improves with immunohistochemistry, molecular analyses, and cytogenetic studies, enhancing diagnosis and treatment, and ultimately leading to better survival rates. Unfortunately, these tests are often not readily available in low and middle-income countries, where childhood cancer rates are highest. We present a case of a male infant who developed a progressive ulcerative mass over a giant congenital melanocytic naevus in the lumbosacral region. Immunohistochemical analysis of the ulcerative mass was positive for Oscar keratin. Despite the high diagnostic uncertainty, the working diagnosis was extra-renal Wilms' Tumor with loco-regional metastasis based on the positive Oscar Keratin. Following the SIOP protocol for Wilms' Tumor management, he underwent neoadjuvant chemotherapy, surgery, and adjuvant chemotherapy. He achieved complete remission with multimodal treatment and is alive 2 years after treatment.