近日，阿姆斯特丹大学的一项研究表明，在中危患者中，第2轮粪便免疫化学试验(FIT)对结直肠癌的阳性预测值(PPV)为第1轮试验的PPV的一半。此外，第1轮愈创木脂粪便潜血试验的PPV与第1轮FIT无显著差异。相关论文发表在《胃肠病学》(Gastroenterology)杂志上。
在这项研究中，阿姆斯特丹大学学术医疗中心的Maaike J. Denters博士及其同事将4,990例50~74岁的中危患者随机分入愈创木脂粪便潜血试验组(n=2,119)或FIT组(n=2,871)。在将试剂盒发放给患者后，通过邮寄形式收回。对愈创木脂粪便潜血试验组患者无饮食方面的要求。2年后，对第1轮试验结果阴性的所有患者发放FIT试剂盒。要求第1轮和第2轮试验结果均阳性的患者到筛查中心接受咨询，并建议进行结肠镜检查，除非存在禁忌证。
共有293例患者的第1轮试验结果为阳性，其中233例来自FIT组，60例来自愈创木脂组。因此，FIT组和愈创木脂组的阳性率分别为8.1%和2.8%。共239例阳性患者进行结肠镜检查。在愈创木脂组53 例阳性患者中，24例患者的最终结果为晚期腺瘤，表明对晚期腺瘤的PPV为45%(晚期腺瘤定义为≥10 mm的任何腺瘤，或伴有20%以上的绒毛成分，或伴有高度异型增生)；8例患者检出结直肠癌，表明对癌症的PPV为15%。在FIT组186例阳性患者中，88例检出晚期腺瘤(PPV=47%)，12例检出癌症(PPV=6%)。总体而言，在第1轮所有阳性患者中，共20例患者检出癌症，提示对癌症的PPV为8%。
在愈创木脂粪便潜血试验后进行FIT的患者中，有122例患者在第2轮试验结果为阳性后进行了结肠镜检查，其中53例检出晚期腺瘤(PPV=43%)，5例检出癌症(PPV=4%)。同样，在FIT后再次进行FIT的患者中，50例检出晚期腺瘤(PPV=38%)，4例检出癌症(PPV=3%)。在第2轮中，共9例患者检出癌症(癌症例数为第1轮的一半)，表明对癌症的PPV仅为4%。尽管第2轮筛查对结直肠癌的PPV明显降低，但该轮筛查检出的腺瘤数量较多。
与其他研究采用的提示FIT阳性的血红蛋白阈值(75 ng/ml或100 ng/ml)相比，该研究所采用的阈值(50 ng/ml)较低，这可能是该研究的局限性所在。研究者表示，在这一阈值进行更多轮的筛查将很可能观察到仍然较高的阳性率，因此需进行的结肠镜检查也较多，而PPV将进一步降低。阈值的选择对于平衡这2个参数至关重要，并且受到经济、行为和其他因素的影响，而且不同国家选择的阈值也各不相同。（生物谷Bioon.com）
doi:10.1053/j.gastro.2011.11.024
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Lower Risk of Advanced Neoplasia Among Patients With a Previous Negative Result From a Fecal Test for Colorectal Cancer
Maaike J. Denters, Marije Deutekom, Patrick M. Bossuyt, An K. Stroobants, Paul Fockens, Evelien Dekker
Background & Aims
Consecutive rounds of fecal occult blood tests (FOBTs) are used to screen for colorectal cancer (CRC); they detect precursor lesions and early-stage disease. We assessed whether the positivity rate and the positive predictive values (PPVs) for advanced neoplasia and CRC decrease with repeated testing by using fecal immunochemical tests (FITs).
Methods
Data were collected from 2 rounds of screening. In the first round, average-risk persons (50 to 74 years old) were randomly assigned to groups that received the guaiac FOBT or FIT. In the second round, the subjects received only FIT (1594 received FIT after guaiac FOBT and 2022 received FIT after FIT). The positivity rate and PPV for advanced neoplasia and CRC were compared between second-round participants with a previous negative test result (FIT after guaiac FOBT or FIT after FIT) and first-round participants (guaiac FOBT or FIT).
Results
The rate of positive results from FIT was 7.4% in the FIT-after-FIT group, compared with 8.1% in the first-round FIT group (P = .34). A significant decrease was observed in the PPV for advanced neoplasia between the first and second round from 55% (132/239) to 44% (112/252; P = .017). The PPV for CRC was 8% (20/239) in the first round versus 4% (9/252) in the second round (P = .024). Ten interval cancers were diagnosed. There were no significant differences in stages of cancers detected in the first and second round or the interval cancers.
Conclusions
The rate of positive results from FIT does not decrease after repeated CRC screening, but the PPVs of FIT for advanced neoplasia and for CRC are significantly lower among second-round participants who tested negative in the first round.
