Improved staging with pretreatment positron emission tomography/computed tomography in low rectal cancer

(18)F-Fluorodeoxyglucose (FDG)-positron emission tomography (PET) and computed tomography (CT) are widely accepted in the evaluation for metastatic or recurrent rectal cancer. Only spiral CT and transrectal ultrasonography (TRUS) are routinely used in the initial evaluation of primary rectal cancer. We wished to determine whether PET/CT could provide additional information in patients undergoing standard evaluation for primary rectal cancer.

Thirty-seven patients (mean age, 58 years; range, 26-90 years) with a previously untreated rectal cancer underwent TRUS or magnetic resonance imaging, spiral CT, and FDG-PET/CT. The tumor location (low, < or =6 cm; mid, 7-10 cm; or high, > or =10 cm) and carcinoembryonic antigen level were recorded. Discordant findings between spiral CT and FDG-PET/CT were confirmed by histological analysis or imaging follow-up.

FDG-PET/CT identified discordant findings in 14 patients (38%), and this resulted in upstaging of 7 patients (50%) and downstaging of 3 patients (21%). Although node-positive disease on TRUS/magnetic resonance imaging was associated with discordant FDG-PET/CT findings, this was not statistically significant. Discordant PET/CT findings were significantly more common in patients with a low rectal cancer than in those with mid or high rectal cancer (13 vs. 1; P = .0027). The most common discordant finding was lymph node metastasis (n = 7; 50%). Histological confirmation of discordant FDG-PET/CT findings was performed in seven patients, and in no case did FDG-PET/CT prove to be inaccurate. Discordant PET/CT findings resulted in a deviation in the proposed treatment plan in 27% of patients (n = 10).

FDG-PET/CT frequently yields additional staging information in patients with low rectal cancer. Improved accuracy of pretreatment imaging with FDG-PET/CT will allow for more appropriate stage-specific therapy.