Laboratory tests There are a variety of laboratory tests that can be performed to diagnose and monitor breast cancer and its treatment. These tests can be broken down into four groups, based on the purpose of testing:
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 area is
benign or
malignant. This determination will guide treatment.
The testing of biopsy material for cancer involves looking at cells under a microscope for evidence that cells have become malignant (changed from normal breast cells to cancer cells). Signs include change in the size of cell nuclei and evidence of increased cell division. Needle aspirations are limited in that they only show if malignant cells are present. A tissue biopsy is needed to determine if the cells are early stage or invasive.
If the pathologist's diagnosis is invasive carcinoma, there are several tests that may be performed on the cancer cells that guide in treatment and prognosis of the patient. The most useful of these are Her-2/neu and oestrogen and progesterone receptors.
- Her-2/neu is an oncogene that is over-expressed in approximately 20% to 30% of invasive breast cancers. It is a protein that is present in very large numbers on the surface of some malignant breast cancer cells, causing these cells to rapidly proliferate. It is important because these tumours are susceptible to treatment with the chemotherapeutic agent Herceptin (Trastuzumab), which blocks the protein receptors, inhibiting continued replication and growth of the tumour cells.
There are two common techniques used to determine Her-2/neu status in breast cancer: immunohistochemistry (a method for detecting the oncoprotein) and fluorescent in situ hybridization (FISH), a powerful technique for detecting gene amplification. Currently, the standard for assessing Her-2/neu status is immunohistochemistry, and the results are scored as 0, 1+, 2+ and 3+ where 0 and 1+ are considered negative results and 2+ (if confirmed by FISH) and 3+ are considered positive. A positive result may make the patient eligible for Herceptin therapy. Women who have Her-2/neu positive tumours may be eligible for subsidised Herceptin therapy in Australia.
- Oestrogen and progesterone receptor status is determined by immunohistochemistry. These are very important prognostic markers in breast cancer, and the higher the percentage of overall cells positive as well as the greater the intensity, the better the prognosis. In tumours that have these receptors, normal female hormones cause the cells to grow. The presence of cells in the tumour being positive for oestrogen and/or progesterone receptors is an indication for treatment.
Other laboratory tests may be used to help determine whether or not the tumour is responding to therapy or if it has recurred. The
CA15-3 tumour marker, if elevated prior to treatment, is one such laboratory test, and is used after treatment to monitor a patient for a recurrence of breast cancer. However, it is important to understand that some cancer-free individuals normally have a level of these substances in their blood and/or urine and that most breast cancers are not associated with increased blood levels of this marker. Therefore, only a medical professional can evaluate whether the results of such a test are cause for concern. In general, CA 15-3 is a poor screening test but an excellent surveillance test in some patients; it is unreliable for detecting cancer but can be used to follow it once it has been diagnosed.
There are additional tests that may be used in breast cancer cases, such as DNA ploidy, Ki-67 or other proliferation markers. However, these are not currently in routine use in Australia and most authorities believe that only Her-2/neu, oestrogen receptors, and progesterone receptors are beneficial. The other tests do not have therapeutic implications and, when compared with grade and stage of the disease, are not independently significant with respect to prognosis. Some research centres use these tests for additional information in evaluating patients, however, most studies have shown that their evaluation offers little to prognosis.
Finally, women who are at high risk for breast cancer because of family history can find out if they have the BRCA-1 or BRCA-2
gene mutation by taking a
blood test. Since the BRCA genes normally help to protect a woman from developing breast cancer, a mutation in either gene indicates that the patient is at higher risk for developing the disease. It is important to remember, however, that not all individuals with a mutation develop breast cancer and that most cases of breast cancer occur in women who lack mutations in either BRCA gene. A
genetic counsellor should explain the meaning of the results and offer advice about options for decreasing risk. Counselling advice should be offered both before testing takes place and after receiving test results.
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