Resumen
Thymic epithelial neoplasms consist of thymomas, thymic carcinoids and thymic carcinomas. Carcinomas are malignant tumors of the thymus; they compromise only 4%-14% of thymic epithelial neoplasms. Thymic carcinoma cells do not resemble healthy cells but similar to cancer cells that originate from other parts of the body and grow more quickly when the tumor is found and more difficult to treat. Thymic carcinoma rarely occurs in children. We reported a case of undifferentiated thymic carcinoma in 11 months old female. After two courses of chemotherapy the patient developed increasing respiratory compression and unfortunately died because of respiratory failure.