Classifying breast cancer

Classifying breast cancer

Research on patterns of gene expression has also suggested some newer ways to classify
breast cancers. The current types of breast cancer are based largely on how tumors look
under a microscope. A newer classification, based on molecular features, divides breast
cancers into 4 groups. This testing, called the PAM50, is currently available but is not
used as yet to make treatment decisions:
Luminal A and luminal B types: The luminal types are estrogen receptor (ER)–positive.
The gene expression patterns of these cancers are similar to normal cells that line the
breast ducts and glands (the inside of a duct or gland is called its lumen). Luminal A
cancers are low grade, tend to grow fairly slowly, and have the best prognosis. Luminal B
cancers generally grow somewhat faster than luminal A cancers and their outlook is not
quite as good.
HER2 type: These cancers have extra copies of the HER2 gene and sometimes some
others. They usually have a high-grade appearance under the microscope. These cancers
tend to grow more quickly and have a worse prognosis, although they often can be treated
successfully with targeted therapies such as trastuzumab (Herceptin) and lapatinib
(Tykerb) which are usually given along with chemotherapy.
Basal type: Most of these cancers are of the so-called triple-negative type, that is, they
lack estrogen or progesterone receptors and have normal amounts of HER2. The gene
expression patterns of these cancers are similar to cells in the deeper basal layers of
breast ducts and glands. This type is more common among women with BRCA1 gene
mutations. For reasons that are not well understood, this cancer is also more common
among younger and African-American women.
These are high-grade cancers that tend to grow quickly and have a poor outlook.
Hormone therapy and anti-HER2 therapies like trastuzumab and lapatinib are not
effective against these cancers, although chemotherapy can be helpful. A great deal of
research is being done to find better ways to treat these cancers.
It is hoped that these new breast cancer classifications might someday allow doctors to
better tailor breast cancer treatments, but more research is needed in this area before this
will be possible