[F]-Fluorodeoxyglucose Positron Emission Tomography in the Diagnosis, Treatment Stratification, and Monitoring of Patients with Retroperitoneal Fibrosis: A Prospective Clinical Study.

Background: The ability to distinguish malignant from benign retroperitoneal fibrosis (RPF) and to select patients who are likely to respond to steroid treatment using a noninvasive test would be a major step forward in the management of patients with RPF.

Objective: To prospectively evaluate the potential of [F]-fluorodeoxyglucose positron emission tomography (FDG-PET) to improve clinical decision-making and management of RPF.

Design, Setting, And Participants: A total of 122 RPF patients were assessed and managed by a multidisciplinary RPF service between January 2012 and December 2015. Of these, 78 patients underwent 101 FDG-PET scans, as well as computed tomography and blood tests. Management was based on the findings from these investigations. Median follow-up was 16 mo.

Results And Limitations: Of the 24 patients with negative [F]-FDG-PET, none (0%) had malignancy on biopsy (negative predictive value 100%). [F]-FDG-PET identified malignancy in 4/4 patients (100%) before biopsy. All four patients had highly avid PET (maximum standardised uptake value ≥4) with atypical avidity distribution. [F]-FDG-PET revealed avidity in 19/38 patients (50%) with normal inflammatory markers and no avidity in 10/63 patients (16%) with raised marker levels. Patients with highly avid PET were significantly more likely to respond to steroids compared to those with low avidity (9/11 [82%] vs 3/24 [12%]; p<0.01) or negative PET (9/11 [82%] vs 0/14 [0%]; p<0.01). Limitations include the small number of patients and the predominance of tertiary referrals, which may represent patients with particularly problematic RPF.

Conclusions: This study has established a promising role for [F]-FDG-PET in optimising and individualising the treatment of RPF.

Patient Summary: This study shows that [F]-fluorodeoxyglucose positron emission tomography scans could reduce the need for biopsy in patients with retroperitoneal fibrosis (RPF). This technique can distinguish cancer from noncancerous RPF, and may be better than blood tests in assessing and monitoring RPF. It also appears to predict a patient's response to steroids, which should allow more individualised treatment.