Embryonal Rhabdomyosarcoma Presenting as Lung Metastasis in an Adult: An Uncommon Presentation.

Rhabdomyosarcoma (RMS) is one of the most common soft tissue sarcomas of adolescents and young adults. Histologically, rhabdomyosarcoma is classified into embryonal, alveolar, pleomorphic, and spindle cell/sclerosing rhabdomyosarcomas with further subcategorization. More than 50% of embryonal rhabdomyosarcoma occur within head and neck. The retroperitoneum and pelvis are less common sites of involvement. Embryonal rhabdomyosarcomas affect mainly, but not exclusively, children between birth and 15 years of age. Alveolar rhabdomyosarcoma tends to affect older patients. The usual metastatic sites include lung, lymph nodes, and bone marrow. We are presenting a case of a 25-year-old male patient with symptoms of breathlessness, easy fatigability, and weight loss. On chest imaging, there were multiple lung nodules. A primary diagnosis of undifferentiated malignant neoplasm was made on lung biopsy. On immunohistochemistry, the malignant cells were positive for myogenin, myoblast determination protein 1 (MyoD1), and desmin. They were negative for neuroendocrine, germ cell, epithelial, melanocytic, and lymphoid markers. Further workup showed an abdominopelvic retroperitoneal mass on abdominal computed tomography (CT) scan. The biopsy on the retroperitoneal mass showed similar morphology and immunohistochemical profile. Unfortunately, the patient's condition deteriorated rapidly in the following weeks, and he passed away.