Can we optimize CEA as a response marker in rectal cancer?

Background and Aim: carcinoembryonic antigen (CEA) is a biomarker commonly used in colorectal cancer. However, its prognostic value is still controversial. Recent studies demonstrate that CEA produced locally by tumor cells has a higher prognostic value compared to serum CEA. This study aimed to determine whether there was an association between the CEA/tumor size ratio (CEA/ExT) and the pathological tumor response in patients with rectal adenocarcinoma (ADC), who underwent neoadjuvant chemoradiotherapy (N-CRT), followed by surgical tumor resection.
Methods: a retrospective study was performed of rectal ADC patients who underwent N-CRT followed by curative surgery between March/2012 and October/2017. CEA and tumor extension for pre-treatment CEA/ExT calculation and the pathological response in the surgical specimen after treatment were analyzed.
Results: eighty-nine patients were included, 60.7 % were male and the mean age was 63.8 ± 10.42. There was a good response to N-CRT in 41.6 % of the patients, tumor downstaging occurred in 83.1 % and a complete pathological response in 23.6 % of cases. The average CEA/ExT was 2.01 ng/ml/cm. In the univariate analysis, higher CEA/ExT values were related to a lower frequency of pathological response (p = 0.04) and to a lower frequency of tumor downstaging (p = 0.02). In the multivariate analysis, CEA/ExT was independently related to tumor downstaging (OR: 0.72; 95 % IC: 0.53-0.98, p-0.036).
Conclusions: lower pre-treatment CEA/ExT values seem to be associated with tumor downstaging and this parameter may be a promising predictor of a more favorable response in patients with rectal ADC undergoing treatment with N-CRT.