Positron Emission Tomography for pretreatment staging and posttreatment evaluation in cancer of the anal canal.

PURPOSE

In recent years, combined modality therapy (CMT) with chemotherapy and radiation has replaced surgery as the preferred treatment for cancer of the anal canal. Clinical staging with computed tomography (CT) scan alone may underestimate the extent of disease. We investigated the utility of positron emission tomography (PET) with 2-deoxy-2[F-18]fluoro-D-glucose (FDG) in the staging and determination of response to CMT.

PATIENTS AND METHODS

From September 1999 to August 2002, 21 patients with cancer of the anal canal were studied prospectively. All patients underwent pretreatment PET, in addition to standard clinical evaluation that included CT scanning. Follow-up PET studies were ordered one month after completion of CMT.

RESULTS

Sites of metastases not observed on CT scan were identified in five of 21 patients (24%). These sites included pelvic lymph nodes (four patients) and distant omental metastasis (one patient). In another patient, PET confirmed the presence of suspected M(1) disease in the liver. Posttreatment PET imaging was less useful. Nine patients had minimal residual PET activity at the primary site on the one-month follow-up PET study, but only three of these subsequently developed local recurrence. In addition, recurrences occurred in three patients (two local, one distant) of the six who had negative posttreatment PET studies.

CONCLUSIONS

FDG-PET, in conjunction with CT scanning, provides additional staging information in cancer of the anal canal. This information may have implications for prognosis and radiotherapy planning. Posttreatment PET scans appear to be of little value in predicting durability of response.