Carcinoembryonic antigen (CEA), one of the most widely used serum biomarkers for colorectal cancer, is not only easily accessible through serum but also has already been confirmed to be useful [1]. In patients with newly diagnosed colorectal cancer, elevated CEA before surgery indicates a poor prognosis. Moreover, failure of the increased CEA after surgery to normalize could indicate the possibility of residual cancer and the requirement of additional treatment. Continuous assessment of serum CEA levels after surgery can also help to detect recurrence.

On the other hand, CEA has some limitations in colorectal cancer. First, the diagnostic power of CEA to detect early-stage colorectal cancer has remained low. A meta-analysis showed that CEA had a sensitivity of only 46% in colorectal cancer, as well as a specificity of 89%, which is not particularly high [2]. This raises doubts regarding the usefulness of CEA, which drives the need for identifying alternative tests for circulating DNA and bloodbased microRNAs. Nonetheless, CEA still undoubtedly remains a non-expensive and readily available approach for diagnosing colorectal cancer.

However, most of the existing studies on CEA have focused on colorectal cancer surgery and chemotherapy instead of neoadjuvant chemoradiotherapy (nCRT). In advanced rectal cancer, nCRT has become an essential treatment modality that should be provided before surgery. Given that the effects of radiation appear in very diverse categories, predicting the effects of treatment remains difficult. This makes the prediction crucial for the appropriate treatment for rectal cancer. Although some studies have suggested the usefulness of CEA for predicting treatment effects after surgery with nCRT, studies on this are still lacking [3-5]. As such, more studies on this matter will certainly help clinicians establish treatment plans for rectal cancer.

The present study suggests that CEA plays a particularly meaningful role in predicting prognosis after nCRT in patients with rectal cancer [6]. As discussed in the limitations of the present study, it is unfortunate that the relationship between tumor response after nCRT and CEA level could not be studied. However, the present study offers valuable insights into the treatment and follow-up of rectal cancer, notwithstanding the limitations. We believe that this alternative role of CEA in patients receiving nCRT will inspire and help many clinicians care for patients with rectal cancer.