Incidental detection of a well-differentiated rectal adenocarcinoma by [18F]-Fluorocholine PET/CT in a patient with biochemical relapse of a prostate cancer

Abstract

We report the case of a 70-year-old man who underwent an 18[F]-Fluorocholine ([18F]-FCH) positron emission tomography combined with computed tomography (PET/CT) after biochemical recurrence of prostate cancer previously treated by prostatectomy in 2012 (Gleason score 5 [2+3], PSA value before prostatectomy 19ng/mL). Early acquisitions centered on the pelvis following the injection of 258MBq of [18F]-FCH showed a rectal focused and intense uptake. The imaging performed 60 minutes after injection from the base of the skull to the upper third of the femur confirmed the presence of this focal uptake related on CT slices to a thickening of the rectal wall. Biopsies of the corresponding lesion allowed the diagnosis of well-differentiated rectal adenocarcinoma. The patient was directed to surgical resection, which was effective in September 2014. Pathology analysis was in favor of a well-differentiated rectal adenocarcinoma invaded the totality of the rectal wall. Fifteen lymph nodes were dissected and were benign. The tumor was classified as T3N0 (UICC 2010 classification). A contrast enhancement CT scan did not show any lesion compatible with rectal cancer metastasis. More and more incidental findings will occur in clinical PET/CT practice. If there are suspicious lesions of a different etiology than that announced in the request, nuclear medicine physicians must be aware of such issues in order to help clinicians to pursue further investigations like endoscopic biopsy for colorectal uptake. Finally, further studies must be performed to confirm the usefulness of [18F]-FCH PET/CT in colorectal cancer compared to [18F]-FDG PET/CT.