18F-FDG PET/CT-based treatment response evaluation in locally advanced rectal cancer: a prospective validation of long-term outcomes

Purpose

To prospectively evaluate the usefulness of ¹⁸F-FDG PET/CT) imaging for predicting histopathological response and long-term clinical outcomes in locally advanced rectal cancer (LARC).

Methods

This prospective study included 38 patients with a confirmed diagnosis of LARC (cT3-4 or cN+) who underwent ¹⁸F-FDG PET/CT before and after neoadjuvant therapy (NAT). Total mesorectal excision was scheduled 6 weeks after NAT and was followed by an expert histopathological analysis of the surgical specimen. Baseline variables and previously identified maximum FDG standardized uptake value (SUVmax) cut-off values before NAT (SUVmax_PRE ≥6) and after NAT (SUVmax_POST ≥2), and the absolute and percentage reductions from baseline SUVmax (?SUVmax <4 and ?SUVmax% <65 %, respectively) were applied to differentiate patients showing a metabolic tumour response from nonresponders. These features were correlated with tumour regression grade (TRG), disease-free survival (DFS) and overall survival (OS).

Results

Significantly higher 5-year DFS and OS were seen in 19 responders (TRG 3 or 4) than in 19 nonresponders (TRG 0–2; 94.4 vs. 48.8 %, p?=?0.001; 94.7 vs. 63.2 %, p?=?0.02, respectively). In multivariate analysis the only PET/CT SUVmax-based parameter significantly correlated with the likelihood of recurrence and survival was ?SUV% <65 % (HR?=?5.95, p?=?0.02, for DFS; HR?=?5.26, p?=?0.04, for OS)

Conclusion

This prospective study proved that ¹⁸F-FDG PET/CT is a valuable imaging tool for assessing rectal cancer TRG and long-term prognosis, and could potentially serve as an intermediate endpoint in treatment optimization research and rectal cancer patient care.