Her2 scores... FISH versus IHC

Generally speaking , those who "overexpress" Her2, or are 3+ on IHC or 2 to 1 ratio on FISH, get Herceptin.  Some amount of Her2 is normal, that is why registering a 1+ or 2+ are considered negative.  There is a developing school of thought that some of those who do not fit the overexpression criteria may still benefit from either Herceptin, or one of the vaccines that is in clinical trials.  I took part in the trial linked below (I am Her2+++ and received a year of Herceptin) that has just been opened to include those who do have a lower registration of HEr2, but did not meet the criteria for Herceptin.

http://clinicaltrials.gov/show/NCT00524277

Here is BCO's explanation:

http://www.breastcancer.org/symptoms/diagnosis/her2

Here is a good explanation, and the answer to your ratio question:

Immunohistochemistry (Immuno-Histo-Chemistry; IHC)

IHC is a protein-based test that is used to provide an assessment of the amount of HER2 protein receptors on the surface of the cancer cells. In HER2-positive tumors there is more than a normal amount of HER2 protein on the cell surface (i.e., there is HER2 protein “overexpression”).

The IHC test is done by a pathologistA doctor who identifies diseases by studying cells and tissues under a microscope. in a laboratory on a sample of a tumor removed during a biopsyThe removal of cells or tissues for examination by a pathologist. The pathologist may study the tissue under a microscope or perform other tests on the cells or tissue. There are many different types of biopsy procedures. The most common types include: (1) incisional biopsy, in which only a sample of tissue is removed; (2) excisional biopsy, in which an entire lump or suspicious area is removed; and (3) needle biopsy, in which a sample of tissue or fluid is removed with a needle. When a wide needle is used, the procedure is called a core biopsy. When a thin needle is used, the procedure is called a fine-needle aspiration biopsy. , a lumpectomySurgery to remove the tumor and a small amount of normal tissue around it. or a mastectomySurgery to remove the breast (or as much of the breast tissue as possible). . The steps in the procedure are as follows:

• Breast cancer tissueA group or layer of cells that work together to perform a specific function. is prepared for testing.
• The sample of tumor (a thin slice) is exposed to an antibodyA type of protein made by plasma cells (a type of white blood cell) in response to an antigen (foreign substance). Each antibody can bind to only one specific antigen. The purpose of this binding is to help destroy the antigen. Antibodies can work in several ways, depending on the nature of the antigen. Some antibodies destroy antigens directly. Others make it easier for white blood cells to destroy the antigen. which attaches to the HER2 receptors.
• The antibody attached to the HER2 protein receptors reacts with other substances that cause a color change in the tissue sample.
• A pathologist must judge the degree of color change in the cells of the sample; the more HER2 protein the darker the staining. Evaluation of the number of cells with color and the color intensity of the cells may be performed with computer imaging methods.
• The percentage of cells in the sample with color, and the intensity of the color of the cells on the slide, determines the score for the test.

The scoring for an IHC test ranges from 0 to 3+.

• Zero is HER2 negative
• 1+ is considered HER2 negative
• 2+ is considered a borderline or equivocal result
• 3+ is HER2 positive

Several potential problems may be encountered with IHC testing:

• The protein being measured can be damaged during certain preparations of the tissue sample, causing variability in test outcomeA specific result or effect that can be measured. Examples of outcomes include decreased pain, reduced tumor size, and improvement of disease. .
• Evaluation of the sample often requires the pathologist to subjectively judge the degree of color (of the HER2 protein on the cell).
• False positive or false negative HER2 test results can occur.

Fluorescence In Situ Hybridization (FISH)

FISH is a gene-based test used to determine the number of HER2 genes in the cells of the tumor. In HER2-positive breast cancer if there are too many copies of the HER2 gene, the gene is “amplified." The FISH test is done by a pathologist in a laboratory on a sample of a tumor removed during a biopsy, a lumpectomy or a mastectomy. The steps in the most commonly used procedure (Pathvysion) are as follows:

• Breast cancer tissue is prepared for testing.
• The sample of tumor (a thin slice) is exposed to fluorescent compounds (will glow under certain lights).
• One fluorescent compound adheres (sticks) to the HER2 genes in a cell and another adheres to chromosome 17 in a cell.
• When the sample is exposed to a special light, the HER2 genes and chromosome 17 light up with different colors and can be counted; a pathologist or computer then reads the prepared slide.
• The proportion or ratio of genes to chromosomes 17 in 60 cells is determined and the average number of HER2 genes/chromosome 17 per cell is then reported.
• The HER2 gene/chromosome 17 ratio in a normal, nondividing cell should be 1 to 1. One gene is on each of the 2 copies of chromosome 17. The HER2 gene/chromosome 17 ratio can increase up to 2 to 1 in cells during certain stages of normal cell division. An average HER2 gene/chromosome 17 ratio of less than 2 to 1 is reported as HER2 negative.
• Tumor samples with an average HER2 gene/chromosome 17 ratio of greater than or equal to 2 to 1 (2.5 to 1, 3.2 to 1, etc.) are reported as HER2 positive.

Another FISH procedure (INFORM) uses a similar procedure but measures only the average number of HER2 gene copies/cell; tumor samples with an average of greater than 4 HER2 gene copies per cell are considered HER2 positive.

Problems encountered in FISH testing include the following:

• Increased cost of FISH relative to IHC HER2 testing.
• Scoring difficulties found with FISH testing may be associated with the specific set of cells chosen to include in the determination or tissue processing.
• False positive or false negative HER2 test results can occur.

NCCN Recommendations

If appropriate quality control/assurance procedures are in place for a laboratory, either the IHC or the FISH method may be used to determine HER2 tumor status. If the laboratory does not have control/assurance procedures in place, the sample should be sent to a reference laboratory that does meet the quality control/assurance procedures.

HER2 test results are interpreted as follows:

• HER2 positive status is IHC 3+ or FISH positive
• HER2 negative status is IHC 0, 1+ or FISH negative
• A borderline IHC result of 2+ should be followed by performing a FISH test.
• A borderline FISH result of an average HER2 gene/chromosome 17 ratio of 1.8 to 2.2 (or an average of greater than 4 to less than 6 HER2 gene copies/cell) should be followed by one of the following:
  • Counting additional cells in the tissue sample
  • Retesting with FISH
  • Performing an IHC test

colt - yes, you do - and it is important to note that you do want to overtreat with the thought that "more is better" if it is not necessary, Herceptin comes with its own set of side effects, including heart damage.  The accepted treatment guidelines mean that at the moment oncologists do not give Herceptin unless you clearly overexpress Her2.  However, being negative by Herceptin treatment standards does not necessarily preclude participation in the vaccine trial I mentioned.  The purpose of this vaccine is to prevent recurrence - the subject you were concerned about in your other thread.

Here is also some other thread info about the developing school of thought...

http://www.breastcancer.org/research-news/20130304