Primary pulmonary sarcomas are exceptionally rare, and pulmonary spindle cell sarcomas represent an even rarer, highly aggressive subset. Their clinical presentation is often nonspecific, and rapid local invasion may culminate in malignant spinal cord compression (MSCC), posing urgent diagnostic and therapeutic challenges. A 60-year-old man with a history of follicular lymphoma treated with O-CHOP and obinutuzumab maintenance subsequently developed a metachronous undifferentiated spindle cell sarcoma of the right upper lobe with pleural dissemination (FNCLCC grade 2). Despite multimodal therapy including cisplatin/etoposide and thoracic radiotherapy, followed by ifosfamide-imaging in June 2025 demonstrated rapid progression. Right-sided video-assisted thoracoscopic surgery revealed a massive, unresectable tumor infiltrating the chest wall. A subsequent gemcitabine/docetaxel regimen was initiated; shortly thereafter, the patient developed acute urinary retention and rapidly progressive lower-limb sensory symptoms evolving to paraparesis. Computed tomography showed a 127 × 99 × 165 mm right upper-lobe mass with osseous invasion and intraspinal extension at Th4–Th6 and Th11–Th12, with additional liver and bilateral renal metastases. Laboratory testing demonstrated severe anemia, thrombocytopenia, and markedly elevated inflammatory markers. Management included transfusion support, high-dose corticosteroids, antibiotics for MRSE urinary infection, and opioid-based analgesia. Given disseminated disease and ECOG 4 performance status, neurosurgical decompression and further systemic therapy were withheld, and the patient was discharged to home hospice. Abrupt neurological deterioration in aggressive thoracic sarcoma mandates urgent evaluation for MSCC; in terminal disseminated disease, early goal-concordant palliative care is essential.