New study is likely to reshape the scientific understanding of breast cancer
Breast cancer kills 35,000 women in the US each year. A new study is likely to reshape the scientific understanding of breast cancer. A team of researchers have identified four genetically distinct types of breast cancer; furthermore, they have unearthed genetic characteristics within the four types that are the basis of many cancers.
They published their findings online on September 23 in the journal Nature.
The study was based on an analysis of tumors from 825 patients; it is a component of a large federal project, the Cancer Genome Atlas, which is developing maps of genetic changes in common cancers. Recently, researchers affiliated with the project have published similar studies on lung and colon cancer. The findings of the study are expected to lead to new treatments with drugs already approved for cancers in other parts of the body as well as the development of more precise treatments aimed at genetic abnormalities that currently have no known treatment.
The investigators caution that it will still take years to translate the new information into new treatment protocols. Within the four major types of breast cancer that they have identifies, individual tumors appear to have different genetic changes. Therefore, the researchers believe that a wide variety of drugs will most likely need to be developed to adapt the pharmaceuticals to individual tumors.
The researchers have identified more than 40 genetic alterations that might be attacked by drugs. Many of them are already being developed for other types of cancer that have the same mutations. The investigators focused on the most common types of breast cancer that are thought to arise in the milk duct. They concentrated on early breast cancers that had not yet metastasized in order to find genetic changes that could be attacked; thus, preventing spread of the cancer to other parts of the body.
Ana analysis of a particularly virulent type of breast cancer revealed a surprising finding. The cells of this cancer resembled basal cells of the skin and sweat glands, which are in the deepest layer of the skin. These breast cells form a scaffolding for milk duct cells. This type of cancer is often called triple negative and accounts for a small percentage of breast cancer. The investigators found that this cancer was entirely different from the other types of breast cancer and much more resembles a type of lung cancer as well as ovarian cancer. The significance of this finding is that it provides a biologic reason to try some routine treatments for ovarian cancer rather than drugs commonly used to treat breast cancer.
Two other types account for most cases of breast cancer. These tumors arise from the cells that line the milk ducts. They contain proteins on their surfaces, which are estrogen receptors. The estrogen fuels the growth of these cells. Women with these two types of cancer undergo a similar treatment protocol; some respond well while others do not. The genetic analysis divided these cancers into two distinct types. Patients with luminal A cancer had a good prognosis; however, women with luminal B did not; this suggested to the researchers that the women with the first kind of tumor might do well with just hormonal therapy to block estrogen from stimulating cancer growth while those with the second kind might do better with chemotherapy in addition to hormonal therapy.
The fourth type of cancer that the researchers identified was named HER2-enriched. Breast cancers often have extra copies of a gene, HER2, which drives their growth. The drug, Herceptin, can block the gene; this medication has changed the prognosis for these patients from one of the worst in breast cancer to one of the best. Herceptin is approved for every breast cancer patient whose tumor produces too much HER2; however, the new analysis finds that not all of these tumors are the same. The HER2-enriched should respond well to Herceptin; the other type might not. The only way to know is to define this situation is to conduct a clinical trial; one is currently being planned. Factors influencing the use of Herceptin are its high cost and a potential to damage the heart; therefore, it should only be given to women who will benefit from it.
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