Joshua M Lawrenz1, Jaymeson Gordon1, Jaiben George1, Collin Haben1, Brian P Rubin2, Hakan Ilaslan3, Nathan W Mesko1, Lukas M Nystrom1. 1. J. M. Lawrenz, J. Gordon, J. George, C. Haben, N. W. Mesko, L. M. Nystrom, Department of Orthopaedic Surgery, Cleveland Clinic, Cleveland, OH, USA. 2. B. P. Rubin, Department of Anatomic Pathology, Cleveland Clinic, Cleveland, OH, USA. 3. H. Ilaslan, Department of Radiology, Cleveland Clinic, Cleveland, OH, USA.
Abstract
BACKGROUND: Patients older than 40 years presenting with osteolytic bone lesions are likely to have a diagnosis of carcinoma, even if they had no prior cancer diagnosis. For patients with no prior cancer diagnosis, there is a well-accepted algorithm to determine a potential primary site. That algorithm, however, leaves approximately 15% of people without a detectable primary tumor site, making treatment decisions extremely difficult. Positron emission tomography (PET) fused with CT, more commonly known as PET/CT, has emerged as an important staging modality for many other malignancies but has been used in a very limited fashion in musculoskeletal oncology. QUESTIONS/PURPOSES: We asked (1) What is the ability of PET/CT to detect the source of the primary tumor in patients with a skeletal metastasis of unknown primary? (2) How does PET/CT perform in detecting metastases in other sites in patients with a skeletal metastasis of unknown primary? METHODS: A retrospective analysis between 2006 and 2016 of the pathology database of a single tertiary center identified 35 patients with a biopsy-proven skeletal metastasis (histologically confirmed carcinoma or adenocarcinoma) and a PET/CT scan that was performed after the standard diagnostic evaluation of the primary cancer site. Patients were identified through use of our pathology database to identify all biopsy-proven bone carcinomas. This was then cross referenced with our imaging database to identify all patients who were at any time evaluated with PET/CT. During this time, we identified 1075 patients with biopsy-proven metastatic bone disease through our pathology database. Any indication for a PET/CT was included, and was most often done for staging of the identified malignancy or evaluation for the unknown source. Data regarding the ability of PET/CT to find or confirm the primary cancer and all metastatic sites were evaluated. The standard diagnostic evaluation (history and physical, laboratory evaluation, CT of the chest/abdomen/pelvis and whole body bone scan) identified the primary cancer in 22 of the 35 patients. Among the 35 patients, there were a total of 176 metastatic sites of disease identified, with 115 identified with the standard diagnostic evaluation (before PET/CT). RESULTS: Among patients with a skeletal metastasis of unknown primary, PET/CT was unable to identify the primary cancer in 12 of 13 patients. PET/CT confirmed the site of the known primary cancer in all 22 patients. There were 176 total metastatic sites. Of the 115 metastases known before PET/CT, PET/CT failed to identify three of 115 (3% false-negative rate). CONCLUSIONS: PET/CT may not provide any additional benefit over the standard evaluation for identification of the primary cancer in patients with a skeletal metastasis of unknown primary, although it may have efficacy as a screening tool equivalent or superior to the standard diagnostic algorithm for evaluation of the overall metastatic burden in these patients. LEVEL OF EVIDENCE: Level III, diagnostic study.
BACKGROUND: Patients older than 40 years presenting with osteolytic bone lesions are likely to have a diagnosis of carcinoma, even if they had no prior cancer diagnosis. For patients with no prior cancer diagnosis, there is a well-accepted algorithm to determine a potential primary site. That algorithm, however, leaves approximately 15% of people without a detectable primary tumor site, making treatment decisions extremely difficult. Positron emission tomography (PET) fused with CT, more commonly known as PET/CT, has emerged as an important staging modality for many other malignancies but has been used in a very limited fashion in musculoskeletal oncology. QUESTIONS/PURPOSES: We asked (1) What is the ability of PET/CT to detect the source of the primary tumor in patients with a skeletal metastasis of unknown primary? (2) How does PET/CT perform in detecting metastases in other sites in patients with a skeletal metastasis of unknown primary? METHODS: A retrospective analysis between 2006 and 2016 of the pathology database of a single tertiary center identified 35 patients with a biopsy-proven skeletal metastasis (histologically confirmed carcinoma or adenocarcinoma) and a PET/CT scan that was performed after the standard diagnostic evaluation of the primary cancer site. Patients were identified through use of our pathology database to identify all biopsy-proven bone carcinomas. This was then cross referenced with our imaging database to identify all patients who were at any time evaluated with PET/CT. During this time, we identified 1075 patients with biopsy-proven metastatic bone disease through our pathology database. Any indication for a PET/CT was included, and was most often done for staging of the identified malignancy or evaluation for the unknown source. Data regarding the ability of PET/CT to find or confirm the primary cancer and all metastatic sites were evaluated. The standard diagnostic evaluation (history and physical, laboratory evaluation, CT of the chest/abdomen/pelvis and whole body bone scan) identified the primary cancer in 22 of the 35 patients. Among the 35 patients, there were a total of 176 metastatic sites of disease identified, with 115 identified with the standard diagnostic evaluation (before PET/CT). RESULTS: Among patients with a skeletal metastasis of unknown primary, PET/CT was unable to identify the primary cancer in 12 of 13 patients. PET/CT confirmed the site of the known primary cancer in all 22 patients. There were 176 total metastatic sites. Of the 115 metastases known before PET/CT, PET/CT failed to identify three of 115 (3% false-negative rate). CONCLUSIONS: PET/CT may not provide any additional benefit over the standard evaluation for identification of the primary cancer in patients with a skeletal metastasis of unknown primary, although it may have efficacy as a screening tool equivalent or superior to the standard diagnostic algorithm for evaluation of the overall metastatic burden in these patients. LEVEL OF EVIDENCE: Level III, diagnostic study.