ERBB2 and gastric cancer: In Fig 5, with a pooled PLR of 17 and a hypothetical pre-test probability of 16% (the median prevalence for the eight studies), the use of serum HER2 as a test for HER2-positive tumor diagnosis would raise the post-test probability to 76%, which means that the probability of gastric cancer patients having tissue-HER-2 positive status increases from 16% to 76% in the event of a positive serum-HER2 test.