Osteoblastic response as a healing reaction to chemotherapy mimicking progressive disease in patients with small cell lung cancer.

The osteoblastic response (OR) phenomenon as a healing reaction during effective chemotherapy-defined by the appearance of new osteoblastic bone lesions while disease response in other tumor sites was well documented-has previously been described for breast and prostate cancer. The purpose of this study was to investigate this phenomenon that could erroneously be interpreted as progressive disease in patients with small cell lung cancer (SCLC) and to establish guidelines for interpretation of follow-up computed tomography (CT) examinations in this situation. Twenty-four patients with newly diagnosed SCLC and bone metastases were retrospectively included in this study. The characteristics of bone lesions in CT examinations were correlated with bone scintigraphy and magnetic resonance imaging, if available. In target lesions the CT density quantified in Hounsfield units (HU) was evaluated at baseline and during follow-up. New osteoblastic lesions occurred during follow-up in 17 of 24 patients. OR was proven in 4 patients and considered most likely in 11 patients; mean density increase in target lesions was 153 HU. The study indicates that osteoblastic response as a healing reaction seems to occur in the majority of patients with SCLC and bone metastases and should not be misinterpreted as progressive disease.