Osteoblastic Bone Reaction Developing During Treatment With Sintilimab and Bevacizumab in a Patient With KRASG12V-Mutant Lung Adenocarcinoma.

Osteoblastic bone reaction, the occurrence of new osteoblastic lesions, is a paradoxical phenomenon during the treatment of cancers and can be defined as disease progression or bone metastases. Osteoblastic bone reactions usually occur in patients who receive treatments such as chemotherapy or hormonal or targeted therapy; however, it is difficult to differentiate them from disease progression or an increase in osteoblastic activity in response to therapy. Although osteoblastic bone reaction in lung cancer has been described in a few reports, it has never been reported in patients with KRAS^G12V-mutant lung adenocarcinoma treated with immunotherapy and antiangiogenesis. Here, we describe a case of a 77-year-old male with KRAS^G12V-mutant lung adenocarcinoma whose osteoblastic bone response was found during treatment with sintilimab and bevacizumab. We showed the course of the disease as well as systematic imaging manifestations of lung cancer with osteoblastic bone reaction and discussed their mechanisms.