Remarkable response to anti-PD-L1 blockade in relapsed and refractory metastatic malignant giant cell tumor of bone: a case report.

[CASE] A 40-year-old man presented with malignant giant cell tumor of bone of the left distal femur. Despite distal femur resection/replacement and adjuvant chemotherapy, he experienced local recurrence and lung metastases. Salvage radiation therapy was ineffective. Biopsy of the tumor showed a PD-L1 tumor proportion score of 40%. Pembrolizumab was initiated and resulted in a major partial response. However, the patient experienced radiation recall pneumonitis necessitating stoppage of pembrolizumab. The patient then experienced another local recurrence.

[CONCLUSION] PD-L1 blockade should be considered for MGCTB expressing PD-L1. Unfortunately, pembrolizumab was stopped, which likely allowed for tumor progression in this case.