Negative 18F-FDG-PET-CT may exclude residual or recurrent disease in anal cancer

The incidence of anal cancer is increasing in Western countries. Fluorine-18 fluorodeoxyglucose (F-FDG) PET-computed tomography (CT) is used in the assessment of anal cancer, but its routine use is not established. The aim of this study was to assess the value of F-FDG-PET-CT in staging and post-treatment assessment in anal cancer and to determine its impact on management.

This was a retrospective analysis of patients with anal cancer treated at the Sussex Cancer Centre who underwent PET-CT between November 2004 and September 2014. Information was retrieved from patient notes and the local cancer register, and verified by referring consultants in all cases.

A total of 75 PET-CT scans in 52 patients were identified, representing 38.5% of patients diagnosed with anal cancer during this period. There were 24 staging scans and 51 post-treatment scans. Management was altered following 45.8% of staging scans and 56.0% of all scans, mostly changing treatment type or radiotherapy volume. Out of 28 positive post-treatment scans, 71.4% were true positives, 7.1% were false positives and 21.4% showed nonspecific uptake. Of the 23 negative post-treatment scans, all remained disease free at clinical/radiological follow-up (median follow-up 25 months). The sensitivity and specificity of post-treatment PET-CT were 100 and 74%, respectively. Negative predictive and positive predictive values were 100 and 71%, respectively.

Evidence is evolving for the use of PET-CT in anal cancer. Because of a high negative predictive value, our series shows that PET-CT can be used in the assessment of treatment response to exclude residual/recurrent disease.