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Laboratory tests

Laboratory tests for breast cancer can be broken down into groups, based on the purpose of testing.

Genetic risk:
BRCA-1 and BRCA-2 gene mutation – Women who are at high risk because of a personal or strong family history of early onset breast cancer or ovarian cancer can find out if they have a BRCA gene mutation. A mutation in either gene indicates that the person is at significantly higher lifetime risk (between 50-80%) for developing the disease. It is important to remember, however, that only about 5% to 10% of breast cancer cases occur in women with a BRCA gene mutation. Genetic counselling should be considered both before testing takes place and after receiving positive test results.

Diagnosis: cytology and surgical pathology
When a radiologist detects a suspicious area (calcifications or a non-palpable mass) on a mammogram, or a lump has been found during a clinical or self-examination, a doctor will frequently request a biopsy. For a biopsy, a small sample of tissue is taken from the suspicious area of the breast so that a pathologist can examine the cells for signs of cancer. There are several types of biopsies (fine needle aspiration, needle biopsy, surgical biopsy) performed to first determine whether the lesion in the breast is benign or malignant. This determination will guide treatment.

Malignant cells show changes or deviations from normal cells. Signs include changes in the size, shape, and appearance of cell nuclei and evidence of increased cell division. Malignant cells can also distort the normal arrangement of cells within breast tissue. Pathologists can diagnose cancer based upon the observed changes, determine how abnormal the cells appear, and see whether there is a single type of change or a mixture of changes. These results help guide breast cancer treatment.

Needle aspiration evaluations are limited due to the small sample that is obtained. A tissue biopsy is often needed to determine if a cancer is early stage or invasive. When a breast cancer is surgically removed (see Treatment), cells from the tumour and sometimes from adjacent tissue and lymph nodes are examined by the pathologist to help determine how far the cancer has spread.

Determine treatment options:
If the pathologist's diagnosis is breast cancer, there are several tests that may be performed on the tissue cancer cells. The results of these tests provide a prognosis and help the oncologist (cancer specialist) guide the woman's treatment. The most useful of these are HER-2/neu and oestrogen receptors and progesterone receptors.

  • HER2/neu is an oncogene associated with cell growth. Normal epithelial cells contain two copies of the HER2/neu gene and produce low levels of the HER2 protein on the surface of their cells. In about 20-30% of invasive breast cancers, the HER2/neu gene is amplified and its protein is over-expressed. These tumours are susceptible to treatment that specifically binds to this over-expressed protein. Drugs that target HER2 include, for example, trastuzumab (Herceptin®). Women with amplified HER2/neu gene respond well to these drugs and have a good prognosis.
  • Oestrogen and progesterone receptor (ER and PR) status are important for predicting the course of the disease and helping to guide treatment. Breast cancer cells that have estrogen and/or progesterone receptors can bind estrogen and progesterone. These female hormones promote cell growth and can "feed" ER- and PR-positive cancers. The higher the percentage of cancer cells that are positive, as well as the greater the intensity (the number of receptors per cell), the better the prognosis. This is because hormone-dependant cancers frequently respond well to hormonal therapy that blocks estrogen or lowers estrogen levels.

Breast cancer cells that are negative for HER2/neu amplification and negative for oestrogen and progesterone receptors are called "triple-negative." This type of breast cancer occurs more often in younger women and in women of African or Hispanic descent. Women with triple negative breast cancer may be predisposed to BRCA mutations.

Triple negative breast cancers tend to grow and spread more quickly than other types and have a worse prognosis. Because the cells do not have amplified HER2/neu, they will not respond to treatment with trastuzumab (Herceptin®). Likewise, they do not have receptors for oestrogen and progesterone and cannot be treated with therapy that blocks the hormones. However, they may be treated with other types of chemotherapy.

Monitor treatment:
Cancer antigen 15-3 (CA 15-3) – this is a protein that is produced by normal breast cells. There is an increased production of CA 15-3 in many women with breast cancer. CA 15-3 does not cause cancer. Rather, the protein is shed by tumour cells and enters the blood, making it useful as a tumour marker to follow the course of the cancer. CA 15-3 is elevated in only about 10% of women with early localised breast cancer but is elevated in about 80% of those with metastatic breast cancer. Blood tests for CA 15-3 may be ordered at intervals after treatment to help monitor a woman for breast cancer recurrence. They are not used as screens for breast cancer but can be used to follow it in some women once it has been diagnosed.

Last Review Date: August 1, 2018