Actually- here is the WHOLE thing:
Is My Tumor Truly Hormone Receptor-Negative?
By Susan Peck, PhD
The steroid hormones estrogen and progesterone stimulate the growth of normal breast tissue, as well as many tumors. This is because breast cells contain specialized proteins, called receptors, for these hormones. After binding the hormone, the estrogen receptor (ER) and the progesterone receptor (PR) turn genes involved in cell growth and survival on and off.
There are two ways to measure the amount of receptors in a tumor. The older method involved labeling the hormone with radioactivity and measuring the amount that bound to a tumor sample. Binding assays are quite accurate but require specialized lab equipment and larger amounts of sample. Also, contamination from non-tumor cells can skew results.
A second method, immunohistochemistry (IHC), is more commonly used today. A tumor sample is placed on a slide and incubated with an antibody, a specialized protein that recognizes the ER or PR. A color reaction makes the receptors visible under a microscope. This method can be performed on small samples and doesn’t require sophisticated lab procedures. But scoring and evaluation is subjective, and results can vary.
The amount of receptor on breast tumor cells can determine whether hormone therapy will be effective. In the past, some women who had a low level of ER or PR expression in their breast cancer cells were considered receptor-negative and thought not to benefit from hormonal therapy. It has now become clear that even low levels of hormone receptors may allow women to benefit from hormonal therapies like tamoxifen and aromatase inhibitors. Currently, the most stringent cutoff point to be considered receptor-positive has been lowered. If a woman has as few as 1 percent of cells positive for hormone receptor by IHC, she may be given a trial of hormonal therapy.
Even within ER-positive tumors, there are subtypes with different prognoses. For example, when investigators in the ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial looked at patient subsets, they found that the decrease in relapses seen with Arimidex versus tamoxifen was even more dramatic in women with ER-positive/PR-negative tumors. These results need to be confirmed in a prospective trial.
Gene microarrays, a new tool to measure the expression of thousands of genes simultaneously, are being used to develop a system for classifying tumors. In the future, the “molecular fingerprint” of a tumor may allow us to conclusively determine the tumors most likely to benefit from hormonal therapies.