Labs testing Breast Cancer Samples make more mistakes than we thought
As reported in the Wall Street Journal 1/4/08;
1. Tailoring cancer therapy to the specific patient and their cancer has been considered a break through.
2. Herceptin is a drug for the treatment of breast cancer that targets the breast cancers of women who test positve for a protein called Her-2.
3. So knowing whether your cancer is Her-2 positive or negative can determine your treatment.
4. Another test tests for the presence of proteins that serve as the receptors of the hormones estrogen and progesterone. If the test is positive, drugs like Tamoxifen can be prescribed to block the hormones.
5. Unlike many other tests that are either positive or negative, the test for Her-2 and estrogen receptors require the pathologist to make a judgement call after looking at a sample of the tissue through a microscope.
6. Another key issue surfaces with these reviews and it is that the FDA does not actually review laboratories and the tests that they do/develop as well as it evaluates new drugs. (In fairness, it must be said that the laboratories do have proficiency requirements to meet to keep their licenses. It is just that they have considerable freedom to 'tweak' the procedures without regulatory approval )
A. A 2006 study was cited where Genentech, a large laboratory experienced in performing the testing, reviewed results from local labs around the country. They found that 14- 16% of those samples judged Her-2 positive were actually negative and 18- 23% of those judged negative were actually positive.
B. A second review of a hormone testing lab in Newfoundland, tissue from 763 patients was retested at another lab and it was found that 317 were actually positive.
C. In an international review, 70% of 105 patients evaluated as negative on the estrogen test were actually positive when reviewed by a more experience laboratory.
D. The Society of Clinical Oncology recently estimated that 20% of the Her-2 tests may be inaccurate.
E. Reviews of hormone receptor tests show that test resutls can be affected depending on how much the samples are heated, which preservative is used, and the length of time from surgery to obtain the sample and the time the test is run.
F. There appears to be a lack of standardization of methodology and criteria to call a sample positive amongst the labs doing the testing.
G. The good news is that many insurances will pay for a 'second opinion' when these tests are done.