Comparison of ⁶⁸Ga-PSMA and ¹⁸F-FDG PET/CT in metastatic workup of renal cell carcinoma

¹⁸F-FDG PET/CT is not currently recommended for the diagnosis and staging of RCC based on updated national and international guideline, however, the role of PET/CT in staging and metastatic workup in RCC is evolving. In general, ¹⁸F-FDG PET/CT is used in high-risk RCC patients with better sensitivity for detecting distant metastasis, providing anatomic and metabolic information. PSMA is expressed in the endothelial cells within the neo-vasculature of various solid malignant tumors including clear cell RCC. Few case reports showed more accurate staging for metastatic RCC with PSMA. Therefore, present study aimed to compare the role of ¹⁸F-FDG and ⁶⁸Ga-PSMA in metastatic work- up RCC. Patients with histopathological and/or radiological confirmed RCC were intravenously injected with 10mCi of ¹⁸F-FDG and 3-5mCi of ⁶⁸Ga-PSMA. Images were acquired at 60 & 45 mins post-injection for ¹⁸F-FDG and ⁶⁸Ga-PSMA respectively, on dedicated PET/CT scanners. Acquired whole body PET/CTs were analysed both visually and quantitatively by two experienced nuclear medicine physicians. Twenty (20) patients (16 male, 4 female) with mean age 56.8± 12.5 years of known RCC underwent ¹⁸F-FDG and ⁶⁸Ga- PSMA PET/CT within atleast 1 week. Of 20 patients, 16 patients had clear cell RCC, while 4 had papillary cell RCC. Three out of sixteen (3/16) patients with clear cell RCC patients and 2/4 with papillary cell RCC had no lesion uptake in PSMA PET/CT. Total 245 lesion were positive in FDG PET/CT, while 138 lesions were seen positive on PSMA PET/CT. Of 20 patients, 5 patients showed concordant lesions and 15 patients showed discordant lesions in ¹⁸F-FDG and PSMA. Of 15 patients with discordant lesions, 12 patients showed more FDG avid lesions than PSMA and 3 patient showed more PSMA expression lesions than FDG avid lesions. Of 3 patients with high PSMA expression, 1 had additional sub- hepatic peritoneal lesion which was later confirmed on FNAC, 1 patient with brain mets were better appreciated with PSMA than FDG PET/CT and in 1 patient PSMA expression was helpful to differentiate between infective and metastatic mediastinal lymph node which was later confirmed by histopathological examination. ⁶⁸Ga- PSMA may be useful as an additional modality to FDG PET/CT for metastatic work in RCC patients and in near future it may be used as surrogate for theranostic modality in patients with limited therapeutic options particularly when high tumor to background ratio (>1) on PSMA PET/CT. (author)