Breast cancer cells have proteins on the surface called receptors. When breast cancer tissue is removed during a biopsy or surgery, the tissue is tested in the laboratory. The test looks for certain receptors. The standard two are estrogen and progesterone.

Breast cancer that tests "positive" for these two female hormone receptors probably developed under the influence of these hormones.

Cancer that is estrogen and progesterone receptor positive has an important treatment advantage over breast cancer that is negative for these receptors.

Receptor positive cancers usually respond well to drugs that block the action of estrogen or progesterone on the cancer cell. (This is in addition to chemotherapy and/or radiation.) For some women who are hormone receptor positive, treatment with a hormone blocker after surgery might be all the treatment they need.

On the other hand, hormone receptor blockers will not be effective for women with hormone receptor negative breast cancer cells.

Regarding the Oncotype DX test, it is most useful for women who may not need chemotherapy to treat the breast cancer, such as women who have:

• A single tumor small enough to be removed by lumpectomy
• No spread of cancer to lymph nodes in the armpit
• Cancer cells that test positive for estrogen only receptors

The Oncotype DX test can help predict whether the breast cancer will come back later on. The cells are analyzed for their genetic make up. Specific genes are measured in the sample.

This helps predict whether the woman's cancer is likely to return. When the test suggests that a return risk is high, the doctor will likely suggest additional treatment -- often chemotherapy -- to help reduce this risk.

Researchers are trying to find other gene tests that can be applied to a wider selection of breast cancer, not only the estrogen positive and negative lymph node ones.