Hormone receptor testing

When someone is diagnosed with invasive breast cancer, the pathologist does not stop at saying it is cancer. They also run tests on the piece of tumor taken at the biopsy to see what it carries on its surface and inside its cells. Two of those tests look for the estrogen receptor and the progesterone receptor, the hormone receptors, and a third is ordered for HER-2, another receptor on the tumor. All three are run on every invasive specimen.

The technique is called immunohistochemistry, and it is simpler than it sounds. Very thin slices are cut from the tissue block and bathed in antibodies made to match the receptor in question. If the receptor is there, the antibody sticks to it; if it is not, the antibody washes away. A second antibody then adds color to that binding, and under the microscope the stain marks exactly the spot where the receptor sits.

That color changes the treatment. A tumor that is hormone receptor positive calls for antiestrogen therapy or an aromatase inhibitor. And when the hormone receptor is positive and HER-2 is negative, that combination has a name of its own: the luminal A subtype, one of the categories used to classify these tumors.

And it helps to be clear about what was measured: the tissue removed at the biopsy. The test describes the tumor.