Development of Symptomatic Bone Marrow Metastasis After Complete Response to Immunochemotherapy in Squamous Cell Lung Carcinoma.

INTRODUCTION: Symptomatic bone marrow metastasis in squamous cell lung cancer after achieving a complete response to immunochemotherapy has not been reported previously. CASE PRESENTATION: A 63-year-old Japanese man was referred to our hospital for further examination of an abnormal chest radiograph. Whole-body computed tomography revealed left hilar swelling and osteolytic lesions. Bronchoscopic examination led to a diagnosis of squamous cell lung carcinoma with multiple bone metastases. He was treated with carboplatin/Nab-paclitaxel and pembrolizumab, and achieved complete response as determined by positron emission tomography with fluorodeoxyglucose-computed tomography. Despite pembrolizumab maintenance therapy for 1 year, thrombocytopenia, anemia, and leukoerythroblastosis occurred. Bone marrow biopsy revealed squamous cell carcinoma cells within fibrotic tissue, confirming the diagnosis of symptomatic bone marrow metastases. The patient died 1 month after this diagnosis. CONCLUSION: Recurrence presenting bone marrow metastasis should be considered in patients with squamous cell lung cancer, even achieving complete response to immunochemotherapy, particularly those with bone metastases.