Background: The osteoblastic bone flare or response is the paradoxical phenomenon of increase in the quantity and/or density of bone lesions in the presence of well-documented disease response to treatment in other tumor sites. It results from the rapid repair and increased osteoblastic activity in bone metastases responding to therapy and therefore represents treatment efficacy. Nevertheless, no reliable markers can differentiate an osteoblastic flare or response from disease progression. In non-small cell lung cancer (NSCLC) osteoblastic bone flare or response has been reported in only a few patients.
Methods: Pre- and posttreatment CT scans of NSCLC patients with osteolytic bone lesions and treated with erlotinib as a single treatment modality were reviewed.
Results: In 3 cases fulfilling these criteria and responding to erlotinib according to RECIST criteria, an osteoblastic bone response was found. With the increasing use of epidermal growth factor receptor tyrosine kinase inhibitors in patients with NSCLC harboring mutations predicting a good response, the osteoblastic response will likely be increasingly seen. Awareness of this phenomenon with epidermal growth factor receptor tyrosine kinase inhibitors is important for physicians treating patients with NSCLC, so that it is not misinterpreted as progressive disease resulting in premature cessation of effective therapy.