Abstract Introduction Squamous cell carcinoma of the lung typically presents with local or intrathoracic manifestations, while distant metastases most often involve the bone, brain, liver, or adrenal glands. Metastatic spread to skeletal muscle and other soft tissue sites is exceedingly uncommon. Recognition of such atypical metastatic patterns is essential, as they may precede or obscure the primary diagnosis. We describe a patient who presented with digital and skeletal muscle metastases as the initial manifestation of underlying pulmonary squamous cell carcinoma. Case A 78-year-old man presented to our center with a rapidly enlarging, non-draining lesion on the left fifth digit and a cyst-like mass in the left antecubital fossa that had developed over two months, along with progressive left hip pain for six months. Punch biopsy of both lesions revealed squamous cell carcinoma. PET/CT imaging demonstrated a hypermetabolic right lower lobe pulmonary lesion with mediastinal, hilar, and cervical lymphadenopathy, as well as abnormal uptake in the left gluteus maximus, distal biceps, antecubital fossa, and flexor surface of the fifth finger. Endobronchial ultrasound-guided biopsy confirmed primary pulmonary squamous cell carcinoma with metastases to skeletal muscle and soft tissue sites. Discussion Metastases to skeletal muscle from lung cancer are exceptionally rare and may closely resemble benign or inflammatory lesions, often causing diagnostic delays. Their presence generally indicates aggressive disease behavior. Hematogenous spread is thought to be the primary route, with factors such as muscle contractile activity, local pH, and metabolite accumulation limiting tumor implantation. Even with advanced imaging, muscle lesions can appear nonspecific and may be misinterpreted as abscesses or soft tissue tumors, highlighting the importance of histopathologic confirmation. Clinically, muscle metastases typically present as localized pain or swelling, and persistent symptoms despite treatment should prompt evaluation for malignancy. In this case, hip pain preceded the development of rapidly enlarging soft tissue lesions in the extremities. PET/CT was pivotal in identifying the primary lung tumor and delineating the extent of dissemination. Prognosis remains poor, and early recognition of atypical metastatic presentations is critical for timely diagnosis and accurate prognostic assessment. This abstract is funded by: None
Javed et al. (Fri,) studied this question.