20% inaccuracy? Wow.

[Rich66]

Came across this in a 2010 post elsewhere. My apologies if it's already been covered.

"ASCO/CAP guidelines recommend that HER2 status be determined for all invasive breast cancer patients. These guidelines caution that current HER2 testing methods (central IHC and FISH) may be inaccurate in up to 20% of cases. HERmark Breast Cancer Assay precisely quantifies HER2 total protein and HER2 homodimer levels in FFPE. HERmark reclassified up to 25% of samples from a cohort of the FinHer Adjuvant Breast Cancer Study. It is not known whether there is a benefit to test by two modalities or not and HERmark is only one a panoply of next generation of HER tests that are available or coming the the market."

[tricia keegan]

Wow thats a high percentage Rich!!! I was 3+ so no mistake made thankfully!

[Rich66]

Hmm.. Not sure this suggests it's an issue of how high the score. Intuitively, you'd think it would be more an issue for borderline FISH. but intuition doesn't always work in cancerland.

[Rich66]

This might also explain a certain percentage of supposed her2 negative patients responding to Herceptin..might just be false negatives.

[AlaskaAngel]

Yes. It has been estimated as between 20-25% for a long time. It is so sad to think of those among that 1/5 to 1/4 who were HER2 pos but weren't given trastuzumab to see if they benefitted from it.

Because I have stayed NED without trastuzumab so far for 9 years I considered whether perhaps I was among those who weren't actually HER2 positive. I was +++ by HercepTest. But given that the original "breast cancer specialist surgeon" who evaluated me originally bypassed 2 successive BI-RADS 4 mammo/ultrasounds by professional radiologists, and she only biopsied after a third radiologist made his recommendation as succinct as possible.... and the tumor size estimate had been 0.6 in June and was 1.6 at surgical removal in January, I do believe it to have been fast-growing enough to probably be accurately HER2+++. (Because I was aware of the false rate, I did ask one onc to have FISH done but she said she wouldn't request it for me unless there were reasons to believe I might have a recurrence.) They weren't doing Ki67 back then, either.

AlaskaAngel

[Soccermom]

Rich,
The original study done on the inaccuracies was done in 2003 or 4. In 2004 I provided the Pathologist at the Regional hospital that did my biopsy the full study article. He assured me that he would make certain that all of his specimens would be tested via FISH in the future. I think it was out of University of Pa.
Marcia
P.S. IHC is the less expensive test..less cost to hospital. First thing I did at MDAnderson was to make sure FISH resting was done.

[Rich66]

The bit I posted mentions IHC and FISH..relative to a newer test. I'm not so sure the 20% is based only on IHC.

AA,
Is Herceptest IHC? Do you still have viable tissue to test otherwise? There has been concern over standardization in labs.

" 0.6 in June and was 1.6 at surgical removal in January," I wonder if that's considered fast growing for 6 months.

[AlaskaAngel]

Yes, the HercepTest is IHC:

"HercepTest™ is a semi-quantitative immunohistochemical assay for determination of HER2 protein (c-erbB-2 oncoprotein) overexpression in breast cancer tissues routinely processed for histological evaluation and formalin-fixed, paraffin-embedded cancer tissue from patients with metastatic gastric or gastroesophageal junction adenocarcinoma."

As mentioned, IHC is less expensive than FISH. The inaccuracy of determination has been generally attributed to analysis done outside central labs, where the test is less frequently done, with less experience in doing them with accuracy. Mine was done at a cancer center in Seattle.

At 10 years out whatever cancer I have is likely changed now. But all of the hit or miss aspects of making decisions about therapy when it is costing all of us lost lives and a fortune to boot is pretty disappointing.

A.A.