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Susanne. There are a number of reports that patients can be HER-2/neu negative by IHC or FISH and have an elevated serum HER-2/neu. This can have a number of reasons. One reason is that the original biopsy showed too few HER-2/neu positive cells to score the specimen positive. This iisn't a mistake by the pathologist but what is seen under the microscope. With respect to IHC, a pathologist scores the patient as HER-2/neu positive if greater than 10% of the cells seen under the microscope are 3+. It is certainly possible that someone who has 5% IHC 3+ cells at the primary diagnosis is designated HER-2/neu negative according to the guidelines for scoring patients. It is also possible that these HER-2/neu positive cells are the ones that spread to other parts of the body and grow. As these HER-2/neu positive tumors grow they can shed the HER-2/neu fragment into the blood. As the tumor grows and goes to more sites, the concentration of shed HER-2/neu can build up to detectable levels in the blood. We can then detect the elevated levels in the serum of the patient with the test. I think it is becoming clear that someone with an initial HER-2/neu status of HER-2/neu negative should be re-evaluated. An elevated serum HER-2/neu can then be used to go back and test the primary tumor again or to test a metastatic lesion. If either the primary or the metastatic lesion is now HER-2/neu positive by IHC or FISH the doctor can consider Herceptin for the patient. At this time, the serum HER-2/neu test is not approved to place patients on Herceptin but it can be informative.
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