Pulmonary Metastasis on TC-99m MDP Bone Scan Mimicking Metastatic Rib Lesions in Breast Cancer

Abstract

Bone scan has been widely employed to detect osteoblastic bone metastasis because of the imaging technique's high sensitivity. However, care should be taken to distinguish false positive bone lesions which result from microcalcification of soft tissue malignancy with real osseous metastasis by correlating other modalities of fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT). We report, for the first time, a patient who was initially diagnosed with stage II left breast infiltrating ductal carcinoma and was under clinical management for 20 years. The patient subsequently presented with thoracic symptoms. Bone scan showed multiple focal uptakes within bilateral thoracic ribs. FDG PET/CT scans, however, showed numerous metabolically active bilateral pulmonary nodules with no osseous lesions in ribs. This case demonstrates abnormal findings on bone scans mimicking metastatic rib lesions from micro-calcified pulmonary metastatic nodules in a patient with breast cancer. Thus, care should be taken to correlate interpretation of high sensitivity but non-specificity bone imaging with other modalities such as FDG PET/CT. Keywords:Whole body bone scan; FDG PET/CT; Breast cancer; Pulmonary metastasis; Bony metastasis SummaryTc-99m MDP whole body bone scan is very sensitive and widely applied for clinical staging, monitoring therapeutic response, and evaluating malignant tumor recurrence in patients with malignant cancers, specifically breast cancer in female patients, prostate cancer in male patients, and other cancers including pulmonary cancers. However, attention should be paid by clinicians when they dictate bone imaging given that the various false positive findings may diminish specificity of the study. We presented a case for the first time that demonstrates abnormal findings on bone scans mimicking metastatic rib lesions from micro-calcified pulmonary metastatic nodules in the patient with breast cancer.