Predictive value of the PET-CT (positron emission tomography-computed tomography) in oesophageal squamous cell carcinoma

Abstract

In Hong Kong, oesophageal squamous cell carcinoma (ESCC) is the 10th leading cancer death cause in Hong Kong and is one of the fatal cancers worldwide due to its rapid progression and poor prognosis. The most effective treatment is surgery, although upfront surgery is only applicable to patients with early disease. For those with locally advanced disease, the current standard of care is neoadjuvant chemoradiotherapy (nCRT) followed by surgery. 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) for diagnosis, staging, and treatment assessment in most of the cases. While it is commonly employed in routine clinical practice, its ability to predict treatment response or prognosis remains controversial. The objective of this study was to evaluate the predictive value of clinical and PET parameters in estimating treatment response and patient outcomes in patients with locally advanced ESCC undergoing nCRT followed by surgery in our institute. We retrospectively reviewed 108 ESCC patients who had undergone curative treatment in Queen Mary Hospital between 2012 and 2018. Each patient had undergone staging PET-CT, followed by nCRT, reassessment PET-CT, and oesophagectomy. Patient- characteristics and tumour-characteristics, including age and gender, tumour-nodal-metastasis (TNM) staging on PET and endoscopic ultrasound (EUS), tumour-to-liver ratio (TLR) of the primary tumour on staging PET-CT and treatment response as per PERCIST criteria on reassessment PET-CT were correlated with Mandard tumour regression grade of the primary tumour, progression-free (PFS) and overall (OS) survivals. In a subset of 40 patients that had undergone both staging and reassessment PET-CT in our unit using the same protocol, individual lymph nodes detected by PET-CT between the two scans were analysed. Our results showed that achieving complete metabolic response (CMR) on PET-CT was predictive of complete (pCR) (0.625 against 0.258, p<0.001) and good pathological (0.813 against 0.500, p=0.003) responses of the primary tumour. Furthermore, achieving CMR was also associated with longer OS (median OS 66 vs 15 months, p=0.02). While nodal staging is not found to correlate with primary tumour response to nCRT, it was an independent prognostic factor for OS. Individual lymph node analysis has shown that only 5/120 (4.2%) of 18F-FDG avid lymph nodes detected on reassessment PET-CT were true positives whereas the majority of histologically confirmed metastatic lymph nodes (46/51, 90%) were non-FDG avid. Our results demonstrated that PET-CT has predictive and prognostic values in the evaluation of treatment response in ESCC; achieving a complete metabolic response (CMR) in the primary tumour is predictive of pCR and prognostic of the better OS. However, caution is needed when interpreting nodal disease status as there are significant false positives and negatives.