High False Positive Rate with the Use of CT and FDG-PET in Post-Remission Surveillance for Hodgkin Lymphoma.
Authors: Zuckerman Dan , Lacasce Ann , Jacobsen Eric , Takvorian Tak , Hochberg Ephraim 
Published: April 2020

Abstract
The role of radiologic surveillance in the follow-up of patients with Hodgkin lymphoma is poorly defined. There is no consensus in the NCCN guidelines regarding the use of CT scans. The use of FDG-PET is discouraged given anecdotal experience with false positives. We have retrospectively analyzed 45 cases of classical Hodgkin lymphoma treated with curative intent at our institutions between 2003 and 2005. All patients received ABVD and had a negative FDG-PET within 6 weeks of completing therapy. Follow-up with surveillance CT scans and PET/CT scans were obtained at the discretion of the treating clinician at 3–6 month intervals for the first 2–3 years of follow-up and then every 6–12 months for the next 2–3 years (median every 6 months). A false positive was defined as a radiologic finding on CT or PET/CT that resulted in either increased frequency of surveillance or medical intervention that was subsequently proven by pathology to be benign or resolved spontaneously on further imaging within 12 months. Of the 45 patients, 29 were women and 16 were men. The median age was 34 (18–71) and the median duration of follow-up was 41 months (12–57 months). Sixteen patients had advanced stage (III or IV) disease. Forty-one (91%) patients are alive and without disease, three patients (7%) are alive with relapsed disease, and one patient (2%) has died from disease. There were 25 patients (56%) for whom scans did not change management; 6 patients (13%) for whom scans revealed relapsed disease (4) or second malignancy (2); and 14 patients (31%) for whom scans proved to be false positives. All 4 relapses were asymptomatic, occurred within 3 to 9 months of completing therapy, and were identified on both CT and PET(3) or CT alone (1). All 4 patients proceeded to salvage chemotherapy and autologous or allogeneic transplantation; one patient died of disease and three have relapsed following transplantation. The 2 second malignancies, which were high-grade sarcomas, were asymptomatic and identified on both CT and PET. Both patients had received XRT and one sarcoma was within the radiation field. There were 17 false positive results identifed in 14 patients during follow-up. Of the 17 false positives, 8 were identified on CT with a normal PET (5 lung lesions, 1 ovarian cyst, 1 retractile testicle and 1 renal cyst), 6 were identified on PET with a normal CT (2 parotid uptakes, 2 thymic “rebounds,” 1 nodal uptake, and 1 splenic uptake), and 3 were identified on CT and PET (1 lung lesion, 1 splenic and hilar adenopathy, and 1 small bowel lesion). The patient with the FDG-avid lung lesion underwent CT-guided FNA of the lesion and bronchoscopy with BAL, both of which were negative. The patient with FDG-avid splenic and hilar nodal lesions underwent splenectomy and was found to have sarcoidosis, from which she has been asymptomatic. In conclusion, there is a high rate of false positives when using CT and/or PET as post-remission surveillance. There were no instances in which PET identified early relapsed disease or second malignancy without corresponding CT findings. In our series, PET had no clinical utility in the surveillance of patients with Hodgkin’s lymphoma in remission.