Review Question - QID 215275

Occult lytic metastatic carcinoma to the bone without an identified primary source after a bone scan and CT of the chest, abdomen, and pelvis is most commonly of lung origin.

Metastatic lesions are the most common cause of destructive lytic lesions of the long bones. Patients with suspected metastatic disease should undergo a CT of the chest, abdomen, pelvis in an effort to identify the primary lesion, which is >90% sensitive. In cases where there is an occult malignancy that has metastasized the extremities, the lung is typically the primary.

Rougraff et al. discuss the diagnostic dilemma of unknown metastatic lesions in 40 patients and the diagnostic steps used to identify the primary tumor source. Their recommendations include history, physical exam, routine laboratory analysis, plain radiographs of the entire bone, chest x-ray, whole-body technetium 99 scan, CT of chest/abdomen/pelvis, and finally a biopsy. Their series indicates that occult metastatic lesions not identified on routine staging studies were most likely of lung origin.

Frassica et al. reviewed current recommendations for evaluation, treatment, and outcomes of patients with metastatic bone tumors through an instructional course lecture.

Shih et al. reviewed 177 patients with skeletal metastases and found that in 30% of the patients, the primary carcinoma could not be diagnosed. Post-mortem studies identified the lung as the most common site of an occult tumor.

Incorrect answers:
Answers 1, 3, 4, and 5: Colon, kidney, prostate, and breast primary tumors commonly metastasize to bone and can lead to pathologic fractures or pain. However, in the absence of a detectable primary tumor, metastatic bone lesions are most often the result of a lung primary, termed occult malignant tumors.