Accuracy of pre-operative 18-fluoride fluorodeoxyglucose positron emission tomography (FDG-PET) in predicting lymph node involvement in colon cancer

Accurate staging of colon cancer is imperative in directing treatment and prognostication. Existing literature on pre-operative accuracy of FDG-PET/CT in detecting lymph node disease often combines colon and rectal cancer, examines rectal cancers alone, and rarely assesses colon cancer in isolation. Our aim was to assess pre-operative utility of FDG-PET/CT in detecting lymph node disease in colon cancer.

A retrospective cohort analysis was performed at a single Australian institution between 2017 and 2022 to identify treatment naive primary colonic tumours. Primary outcome was sensitivity and specificity using formal surgical histopathology as gold standard. Secondary outcomes were patient and tumour factors predictive of FDG-PET/CT positive disease including pre-operative CEA, mismatch repair status, duration to surgery, and tumour T-stage.

Three hundred and thirty-nine patients were identified. Thirty-four had pre-operative FDG-PET/CT without neoadjuvant therapy. The mean surgical lymph node harvest was 18 nodes. Twenty-five patients had moderately differentiated tumours. The median duration between FDG-PET/CT and operation was 17 days. Pre-operative FDG-PET/CT suggested positive lymph node involvement in 12 patients. Compared to final lymph node histopathology, FDG-PET/CT had a sensitivity of 53%, specificity of 82%, positive predictive value of 75%, negative predictive value of 64% and accuracy of 68%. There was no significant difference between groups for secondary outcomes.

FDG-PET/CT has moderate specificity but poor sensitivity in the detection of lymph node involvement in colon cancer. Its utility should likely remain isolated to investigating equivocal lesions or follow up of known PET avid disease.