Evaluation of the Role of Positron Emission Tomography (PET) in Patients with Suspected Paraneoplastic Syndrome

Objectives Paraneoplastic syndromes (PNS) are a diverse and uncommon group of diseases related to indirect effects of malignancy. Symptoms are likely immune-mediated and often precede detection of the underlying malignancy. Patients may undergo extensive (and possibly low-yield) evaluations, including FDG PET/CT, to detect the primary tumor. However, the usefulness of FDG PET/CT in this setting is not well established. The purpose of this study is to evaluate the role of FDG PET/CT in suspected PNS.

Methods We performed a retrospective review of the results of 204 FDG PET/CTs performed at our institution for suspected PNS from 2006-2014. Study reports were classified into 3 categories - suggestive of malignancy (positive) / abnormal but not specific for malignancy (indeterminate) / no evidence of malignancy. Clinical chart review was performed for those in the first two categories.

Results Of these studies, 25 (12.3%) showed findings suggestive of malignancy, 56 (27.4%) demonstrated findings indeterminate for malignancy, and 123 (60.3%) showed no evidence of malignancy. Further clinical evaluation of the 25 patients with positive studies yielded 14 cases (56%) of pathology-confirmed malignancy. Of the 56 patients in the indeterminate category, 9 patients (16%) had pathology-confirmed malignancy. Lung cancer (including histological subtypes of squamous cell, small cell, and adenocarcinoma) and lymphoma (including B and T cell histology) represented the most common malignancies detected.

Conclusions In the setting of suspected PNS, FDG PET-CT had a relatively low rate of detection of primary malignancy (11.2%). Still, the cancer detection rate in patients with PNS is greater than in screening programs utilizing FDG PET/CT to detect occult cancer in the general population (1-2%). Further studies are necessary to determine whether FDG PET-CT may be of greater yield for particular subpopulations of patients with PNS (such as those with positive paraneoplastic antibodies).