Diagnosis of certain skeletal metastases may not be improved much by using PET/CT

LAS VEGAS — Due to its access challenges, additional radiation exposure for patients and inability to identify the primary cancer in 92% of patients with a skeletal metastasis of unknown primary or SMUP, researchers concluded PET/CT may not provide the added benefits it is believed to have.

Joshua M. Lawrenz, MD, of the Cleveland Clinic, said at the American Academy of Orthopaedic Surgeons Annual Meeting, “PET/CT shows minimal utility in identifying the primary cancer after unsuccessful standard diagnostic evaluation, though PET/CT may be useful as a confirmatory tool for primary cancer sites or a screening tool for metastatic burden.”

Lawrenz and colleagues studied the diagnostic performance of PET/CT in identifying SMUP due to limited data regarding its use as part of an effective workup in these cancer patients.

In a retrospective study of a 10-year period, researchers included 182 adult patients at their institution who had a standard diagnostic evaluation to identify their primary cancer, were diagnosed with a proven skeletal metastasis and had results of a PET/CT in their medical record. After the researchers excluded patients for various reasons, 35 patients were included in the final analysis.

“Thirteen patients had skeletal metastasis of unknown primary in that they failed to identify the primary cancer site with the standard diagnostic evaluation,” Lawrenz said. “In 22 patients with a known primary cancer, PET/CT confirmed a primary cancer location in all 22 patients; cancers most commonly of the lung. In the 13 patients with a skeletal metastasis of unknown primary, subsequent PET/CT newly identified the primary cancer in one patient and that was in the lung. Twelve of 13 patients remained unidentified at time of follow-up.”

In a secondary analysis that looked at how well PET/CT performed to identify or confirm metastatic sites, PET/CT found 61 new areas of uptake, according to Lorenz.

There was “a 92% positive predictive value of PET/CT in identifying new metastases. Of the 115 metastases known prior to PET/CT, PET/CT failed to identify three, lending itself to a 97% sensitivity in confirming metastatic sites,” he said.

A notable limitation of the study was the small patient cohort, Lorenz noted.

“One possible conclusion that can be drawn from this study is that given the 100% confirmation rate of PET/CT in confirming primary malignancies, that potentially PET/CT should replace standard diagnostic evaluation with no less accuracy,” he said. – by Susan M. Rapp

Reference:

Lawrenz JM, et al. Abstract 125. Presented at: American Academy of Orthopaedic Surgeons; March 12-16, 2019; Las Vegas.

Disclosure: Lawrence reports no relevant financial disclosures.