Pulmonary Pleomorphic Carcinoma Mimicking Primary Sarcoma of the Neck: A Case Report and Literature Review.

We describe our challenge in diagnosing an unusual and rapidly progressing case of pulmonary pleomorphic carcinoma (PPC)-a rare, poorly differentiated, or undifferentiated non-small-cell carcinoma that can metastasize locally or distantly and has a poor prognosis. Our patient was an elderly man with a one-month history of abdominal pain, anorexia, and weight loss, diagnosed with atrophic gastritis via endoscopy, and treated medically without improvement. A week later, this patient developed pain in the head, neck, and shoulder area, and further examination revealed a thickening of his left neck and shoulder, with no palpable lymph nodes. Computed tomography (CT) of the neck, chest, and abdomen led us to believe that we might be dealing with primary sarcoma of the neck since no lung mass was evident. Further investigation could not be performed because the patient's status deteriorated rapidly. An autopsy revealed that soft tissue in the left neck and the mesentery was invaded by poorly differentiated polymorphic malignant cells, which were also seen in the lung lesion. Immunohistochemically, these malignant cells were all positive for AE1/AE3, CAM5.2, TTF-1, Napsin-A, and Vimentin. The cells were also positive for programmed death-ligand 1 staining with a low level of tumor proportion score (over 1%). The final diagnosis was PPC with metastases to soft tissues in the left neck and the mesentery. A review of previous case reports of PPC revealed that soft tissue is an uncommon site for metastasis, and that our CT findings were rather unusual. We hereby present our case and review of published case reports, with the hope that an awareness of the heterogeneous features of PPC could prompt timely biopsy and histological diagnosis.