Stage IV squamous lung cancer: complete response followed by fatal bone marrow metastasis

What happened, in summary

This 63-year-old Japanese man had been followed without recurrence for 7 years after gastrectomy for gastric cancer. In July 2023, routine whole-body CT found thickening of the left main bronchial wall and swelling of the left hilar lymph nodes. FDG-PET/CT showed uptake in those lung and nodal areas and also revealed multiple bone lesions, including the spine and both humeri and femurs. Endobronchial ultrasound-guided transbronchial needle biopsy confirmed squamous cell carcinoma of the lung. He began systemic treatment with carboplatin, nab-paclitaxel, and pembrolizumab. After 6 cycles, chest CT showed resolution of the left main bronchial thickening and disappearance of the left hilar lymphadenopathy. FDG-PET/CT also showed complete resolution of uptake in the previously identified lesions, so the response was considered complete. He continued pembrolizumab maintenance for more than 1 year. He was later admitted with general fatigue, appetite loss, and rapidly worsening anemia and thrombocytopenia. Blood testing showed leukoerythroblastosis and rising SCC antigen and CYFRA tumor markers. Bone marrow aspiration produced a dry tap, so biopsy was performed. The marrow contained malignant cells in fibrotic tissue, and immunohistochemistry was positive for pan-cytokeratin AE1/AE3 and p40, confirming bone marrow metastasis from squamous lung cancer. PD-L1 expression in the metastatic tumor cells was high at 95%. He received multiple blood transfusions but died of aspiration pneumonia 1 month after admission. The relapse was especially dangerous because the marrow involvement caused falling blood counts, leaving few hematopoietic cell nests and making additional chemotherapy difficult despite the tumor’s very high PD-L1 expression.