Pilot study of serial FLT and FDG-PET/CT imaging to monitor response to neoadjuvant chemoradiotherapy of esophageal adenocarcinoma: correlation with histopathologic response.

OBJECTIVE

The aim of this prospective pilot study was to investigate the potential of serial FLT-PET/CT compared to FDG-PET/CT to provide an early indication of esophageal cancer response to concurrent neoadjuvant chemoradiation therapy.

METHODS

Five patients with biopsy-proven esophageal adenocarcinomas underwent neoadjuvant chemoradiation (Tx) prior to minimally invasive esophagectomy. The presence of residual tumor was classified histologically using the Mandard et al. criteria, categorizing patients as pathologic responders and non-responders. Participants underwent PET/CT imaging 1 h after intravenous administration of FDG and of FLT on two separate days within 48 h of each other. Each patient underwent a total of 3 scan "pairs": (1) pre-treatment, (2) during treatment, and (3) post-treatment. Image-based response to therapy was measured in terms of changes in SUVmax (ΔSUV) between pre- and post-therapeutic FLT- and FDG-PET scans. The PET imaging findings were correlated with the pathology results after surgery.

RESULTS

All tumors were FDG and FLT avid at baseline. Lesion FLT uptake was lower than with FDG. Neoadjuvant chemoradiation resulted in a reduction of tumor uptake of both radiotracers in pathological responders (n = 3) and non-responders (n = 2). While the difference in the reduction in mean tumor FLT uptake during Tx between responders (ΔSUV = - 55%) and non-responders (ΔSUV = - 29%) was significant (P = 0.007), for FDG it was not, [responders had a mean ΔSUV = - 39 vs. - 31% for non-responders (P = 0.74)]. The difference in the reduction in tumor FLT uptake at the end of treatment between responders (ΔSUV = - 62%) and non-responders (ΔSUV = - 57%) was not significant (P = 0.54), while for FDG there was a trend toward significance [ΔSUV of responders = - 74 vs. - 52% in non-responders (P = 0.06)].

CONCLUSION

The results of this prospective pilot study suggest that early changes in tumor FLT uptake may be better than FDG in predicting response of esophageal adenocarcinomas to neoadjuvant chemoradiation. These preliminary results support the need to corroborate the value of FLT-PET/CT in a larger cohort.