Evolution of bone metastases in patients receiving at least three months of checkpoint inhibitors.

Background: To investigate the evolution of bone metastases in patients receiving immune checkpoint inhibitors (ICI).

Methods: A single-center retrospective study included cancer patients with bone metastases treated with ICI at our institution between January 2014 and September 2019. Clinical and biological data were collected from medical records and independent expert review of imaging was performed. Target and non-target lesions were identified and followed up to 1 year. Patients were then classified as bone responder or non-responder. Comparisons between groups were performed with Student's t test or Mann-Whitney test.

Results: Among 1108 patients screened, 192 patients had bone metastases and 48 patients were included in the final analysis, with lung cancer, renal carcinoma and melanoma as most represented cancer type. Half of the patients experienced stability, condensation or peripheral sclerosis of bone lesions. Initial progression before stabilization with or without sclerosis of bone lesion occurred for 19% of patients (pseudoprogression). There was an association between bone response and global oncological outcomes. Bone responder patients had a significant decrease in morphine and co-analgesic prescription as well as a significant decrease in alkaline phosphatases compared to non-responder patients.

Conclusion: Bone response was observed in half of patients with available imaging and follow-up after 3 months of ICI treatment, with sclerosis observed in one-third of bone lesions at month 3, in all tumor types. Up to 20% of patients experienced a pseudoprogression of bone lesions such as previously described in primary tumor and other metastatic sites. Bone response was associated with improvement of pain and survival.