Immune-related osteoblastic bone alterations mimicking bone metastasis in a small-cell lung cancer patient treated with durvalumab: a case report.

Background: Chemotherapy combined with immunotherapy is currently the standard first-line treatment for advanced small-cell lung cancer (SCLC). Immunotherapy can induce specific adverse events, called immune-related adverse events (irAEs). IrAEs of bones have rarely been reported. However, identifying bone irAEs could be important in avoiding misdiagnosis and ensuring appropriate patient management. This is the first report describing the diagnosis of irAEs of osteoblastic bone changes mimicking bone metastasis in a SCLC patient treated with durvalumab.

Case description: In this report, we describe a unique and challenging case in which a 54-year-old female patient with SCLC treated with durvalumab, an immunotherapy drug, exhibited osteoblastic bone changes that appeared similar to bone metastasis on imaging but were actually a side effect of immunotherapy. Before treatment, imaging revealed no bone metastasis. In the third month after treatment with durvalumab, computed tomography (CT) revealed multiple bone alterations, predominantly osteoblastic lesions with minor osteolytic changes. Various imaging tests suggested bone metastasis, but she had no symptoms related to bone disease. Notably, the lesions in the chest had achieved a partial response. Based on a comprehensive analysis of the CT-guided pathological biopsy results, the patient's symptoms, and the biological characteristics of SCLC, we determined that these bone changes were irAEs occurring in the skeletal system. The patient was followed up for 10 months, during which time the bone lesions remained stable.

Conclusions: IrAEs of bones are rare, and their manifestations vary. Sometimes, the imaging manifestations of bone irAEs are difficult to distinguish from bone metastasis. If patients show variable treatment responses between different lesions, careful evaluation (including a pathological biopsy) is necessary.