Can carcinoembryonic antigen replace computed tomography in response evaluation of metastatic colorectal cancer?

Introduction: Response Evaluation Criteria in Solid Tumours (RECISTs 1.1) define computed tomography (CT) as the gold standard in response evaluation of patients with metastatic colorectal cancer (mCRC) who are undergoing chemotherapy. The aim of this study was to evaluate whether carcinoembryonic antigen (CEA), which is cheaper and easier to perform, can replace repeated CT. Material and methods: The study included 66 patients with non-resectable mCRC participating in a phase I–II study. CEA values were determined, and CT images were taken every 2 months. CT images were externally and retrospectively reviewed according to the RECIST 1.1 criteria. Different cut-off values for CEA change in percent (DeltaCEA%) compared with baseline or nadir value underwent testing to find patients with disease control (that is stable disease, partial or complete response) at 2, 4, 6 and 8 months, in order to identify those who could have continued with chemotherapy based on CEA values alone. CT verification is needed in progressive disease (PD), and therefore identifying PD patients was our secondary endpoint. Results: The results showed that by using a cut-off value of 0 for DeltaCEA%, disease control was seen in all patients at all measuring points (negative predictive value (NPV) = 1.0). Secondarily, increasing CEA was able to identify all PD patients (sensitivity (Se) = 1.0) and in 50–74% of the patients increasing CEA provided a lead time to PD on upcoming CT. It was possible to replace CT with CEA in all patients with decreasing CEA, meaning that 23–47% of CT scans could have been avoided at any given time point. Conclusion: When the CEA level at a certain measuring point is the same or lower than CEA at baseline or at nadir (the measuring point with the lowest CEA value) during treatment, CEA can replace CT.引言：实体瘤疗效评价标准1.1版（Response Evaluation Criteria in Solid Tumours 1.1，RECIST 1.1）将计算机断层扫描（computed tomography，CT）确立为接受化疗的转移性结直肠癌（metastatic colorectal cancer，mCRC）患者疗效评估的金标准。本研究旨在评估成本更低、操作更简便的癌胚抗原（carcinoembryonic antigen，CEA）能否替代重复CT检查。 材料与方法：本研究纳入66例不可切除转移性结直肠癌患者，均参与Ⅰ-Ⅱ期临床试验。每2个月检测癌胚抗原水平并采集CT影像。由外部机构依据RECIST 1.1标准对CT影像进行回顾性阅片。通过测试相较于基线值或最低值（nadir value）的癌胚抗原变化百分比（DeltaCEA%）的不同截断值，以识别在2、4、6及8个月时达到疾病控制（即疾病稳定、部分缓解或完全缓解）的患者，从而筛选出仅通过癌胚抗原检测结果即可判断是否可继续接受化疗的人群。疾病进展（progressive disease，PD）需经CT验证，因此识别疾病进展患者为本研究的次要终点。 结果：结果显示，当DeltaCEA%截断值设为0时，所有测量节点的患者均达到疾病控制（阴性预测值（negative predictive value，NPV）=1.0）。其次，癌胚抗原升高可识别所有疾病进展患者（灵敏度（sensitivity，Se）=1.0），且在50%~74%的患者中，癌胚抗原升高可提前于后续CT检查发现疾病进展征象。对于癌胚抗原水平下降的患者，可完全用癌胚抗原检测替代CT检查，即任意时间点均可减少23%~47%的CT扫描量。 结论：当某一测量节点的癌胚抗原水平等于或低于治疗期间的基线值或最低值时，癌胚抗原可替代CT检查用于疗效评估。