Multiple primary malignancies: sequential development of Ewing sarcoma and carcinoid tumor in a single patient.

Introduction and importance: Multiple primary malignancies (MPMs) involve two or more distinct primary cancers in one individual, either simultaneously or at different times. The incidence of MPMs is rising due to advancements in cancer detection, improved survival rates, and long-term treatment effects. This case report, likely the first of its kind, highlights a rare instance of a 30-year-old female developing a carcinoid tumor 5 years after Ewing sarcoma, emphasizing the need for vigilant monitoring of cancer survivors. Case presentation: A 30-year-old female with a history of Ewing Sarcoma diagnosed 5 years prior, initially presenting with a vascular, hard mass on her right shoulder, underwent neoadjuvant chemotherapy and surgical excision. She recently presented with high-grade fever, cough, weight loss, and severe chest pain. Imaging and biopsy confirmed a high-grade carcinoid tumor. Histopathology showed positive markers for Synaptophysin, CD56, and Chromogranin, with a Ki-67 index of 30-40%. The patient passed away after one cycle of chemotherapy. Clinical discussion: Diagnosing and managing MPMs is challenging due to the complexity of distinguishing primary tumors from metastases. This case fits the Warren and Gates' criteria for MPMs. This case confirmed Ewing sarcoma and atypical carcinoid tumor as distinct primary malignancies. Delayed diagnosis worsens outcomes, especially for aggressive atypical carcinoids. This case underscores the importance of thorough diagnostics, long-term follow-up, and improved healthcare infrastructure. Conclusion: This case report emphasizes the importance of a multidisciplinary approach, regular follow-ups, and timely detection for effective management of MPMs.