Gastric adenocarcinoma is typically diagnosed using upper endoscopy and managed with radical gastrectomy and, in some cases, chemoradiation; nevertheless, long-term survival is poor. Researchers in a region with a relatively high incidence of gastric adenocarcinoma are evaluating a novel screening test for early detection of the malignancy in high-risk patients. The novel test is based on the measurement of a recently discovered serologic marker of gastric adenocarcinoma, MGAc. Based on results of a large study sample of representative high-risk patients screened with MGAc and diagnosed with gastric adenocarcinoma, the mean survival of patients since time of diagnosis is 8.2 months. A review of records shows that, compared to these patients, similar high-risk patients who were diagnosed using the traditional endoscopic modality had a statistically significant lower mean survival of 7.1 months, with no statistically significant differences in the rates of radical gastrectomy or in the average number or intensity of chemoradiation cycles. Which of the following best explains these results?
A)Lead-time bias
B)Length-time bias
C)Low sensitivity
D)Recall bias
E)Selection bias

Question

Gastric adenocarcinoma is typically diagnosed using upper endoscopy and managed with radical gastrectomy and, in some cases, chemoradiation; nevertheless, long-term survival is poor.  Researchers in a region with a relatively high incidence of gastric adenocarcinoma are evaluating a novel screening test for early detection of the malignancy in high-risk patients.  The novel test is based on the measurement of a recently discovered serologic marker of gastric adenocarcinoma, MGAc.  Based on results of a large study sample of representative high-risk patients screened with MGAc and diagnosed with gastric adenocarcinoma, the mean survival of patients since time of diagnosis is 8.2 months.  A review of records shows that, compared to these patients, similar high-risk patients who were diagnosed using the traditional endoscopic modality had a statistically significant lower mean survival of 7.1 months, with no statistically significant differences in the rates of radical gastrectomy or in the average number or intensity of chemoradiation cycles.  Which of the following best explains these results?
A)Lead-time bias
B)Length-time bias
C)Low sensitivity
D)Recall bias
E)Selection bias

Quizplus · Accepted Answer

Explanation: 11ec2b69_c0e5_0e1e_8f63_bd0bffa64d68_MD0005_00 An ideal screening test detects the disease early enough to allow for an intervention that improves morbidity or mortality. However, bias could lead to incorrect conclusions about the test. Lead-time bias, a common bias seen with screening tests, occurs when a test diagnoses a disease earlier than another test. As a result, the time from diagnosis until death ("apparent survival period") appears prolonged, even though there is no actual improvement in survival. Compared to traditional endoscopic evaluation, use of the novel serologic test for gastric adenocarcinoma screening was associated with a statistically significant apparent increase in survival (since time of diagnosis) by ~1 month (8.2 - 7.1 months); however, the comparable gastrectomy rates and chemoradiotherapy courses suggest that the serologic marker had no impact on management or actual (as opposed to apparent) survival. In other words, the new test gives the appearance that patients' survival is increased, but only because it is able to diagnose the disease earlier; the intervention does not change how long the patients live. (Choice B) Length-time bias results when subjects with a rapidly progressive form of disease are less likely to be detected by screening compared to those with slowly progressive disease. Patients with slowly progressive disease tend to be asymptomatic for a longer period, increasing the likelihood that they will be diagnosed based on screening rather than clinical symptoms. This may give the impression that screening improves disease survival, whereas in actuality it only identifies more benign cases. There is no indication that the patients identified by the serologic marker have more benign forms of cancer given their management. Length-time bias (Choice C) Sensitivity, the ability of a test to correctly identify patients with a disease, is important for a screening test; a negative result on a sensitive test helps to rule out a disease. The comparable gastrectomy rates and chemoradiotherapy courses suggest that the sensitivity of the serologic test is likely high, as it identified patients with gastric adenocarcinoma as well as endoscopy did. (Choice D) Recall bias can distort the results of a case-control study because the investigators must rely on the accounts of exposure from the participants in the study. (Choice E) Selection bias often refers to systematic differences between groups in terms of treatment response or prognosis. The high-risk patients studied were part of a large and representative study sample, and they had gastrectomy rates and chemoradiotherapy courses comparable to those of patients diagnosed endoscopically. This makes selection bias less likely. Educational objective: Lead-time bias is a common bias seen with screening tests. It occurs when a test diagnoses a disease earlier than another test does. As a result, the time from diagnosis until death appears prolonged even though there is no actual improvement in survival.

Gastric Adenocarcinoma Is Typically Diagnosed Using Upper Endoscopy and Managed