Use of low-dose aspirin associated with improved performance of test for detecting colorectal cancer

"Screening for colorectal cancer (CRC) and its precursors by fecal occult blood tests (FOBTs), which has been shown to reduce CRC incidence and mortality in randomized trials, is widely recommended and applied in an increasing number of countries. Screening is mostly done in age groups in which use of low-dose aspirin for primary or secondary prevention of cardiovascular disease is increasingly common. Use of low-dose aspirin increases the likelihood of gastrointestinal bleeding, especially upper gastrointestinal bleeding. Because of the increased risk of bleeding from sources other than colorectal neoplasms [tumors], concerns have been raised regarding possible adverse effects on specificity of FOBT-based screening for CRC," according to background information in the article. Potential false-positive test results due to increased risk of upper gastrointestinal bleeding are expected to be of less concern for increasingly available immunochemical FOBTs (iFOBTs; a type of test to check for blood in the stool), but evidence is sparse about the performance of iFOBTs for patients who use low-dose aspirin.

Hermann Brenner, M.D., M.P.H., of the German Cancer Research Center, Heidelberg, Germany, and colleagues assessed the association of use of low-dose aspirin with performance of 2 iFOBTs in a large sample of women and men who underwent CRC screening. The study, conducted from 2005 through 2009, included 1,979 patients (average age, 62.1 years): 233 regular users of low-dose aspirin (167 men, 67 women) and 1,746 who never used low-dose aspirin (809 men, 937 women). The researchers analyzed measures of sensitivity and specificity in detecting advanced colorectal neoplasms (colorectal cancer or advanced adenoma [a tumor that is not cancer]) with 2 quantitative iFOBTs (hemoglobin test and hemoglobin-haptoglobin [a protein] test).

Advanced neoplasms were found in 24 users (10.3 percent) and 181 nonusers (10.4 percent) of low-dose aspirin. The researchers found that for the hemoglobin test, sensitivity was 70.8 percent for low-dose aspirin users compared with 35.9 percent for nonusers; specificity was 85.7 percent for users compared with 89.2 percent for nonusers. For the hemoglobin-haptoglobin test, sensitivity was 58.3 percent for users compared with 32 percent for non-users and specificity was 85.7 percent for users compared with 91.1 percent for nonusers.

"We provide a detailed comparison of the diagnostic performance of 2 quantitative iFOBTs among users and non-users of low-dose aspirin in the target population for CRC screening. For both tests, sensitivity was markedly higher, while specificity was slightly lower among users of low-dose aspirin compared with nonusers," the authors write.

"… our study strongly suggests that use of low-dose aspirin does not hamper testing for fecal occult blood by immunochemical tests. On the contrary, our findings raise the hypothesis that test performance may be enhanced by temporary use of low-dose aspirin, a hypothesis that needs replication in larger samples and followed up in further research, ideally including randomized trials and different types of FOBTs."