Breast Cancer Genetic Types

In recent years, the medical community’s understanding of the different gene mutations in breast cancer has grown considerably due to advancements in gene detection technology and our understanding of the human genome.

This has ushered in a new era of breast cancer classification based on gene analysis techniques called microarray analysis. The results of this analysis have determined the existence of four distinct types of breast cancer:

  • Luminal A.
  • Luminal B.
  • Basal cell (also referred to as triple-negative).
  • HER2-positive.

If you have been diagnosed with breast cancer, your cancer will be categorized into one of the four types of breast cancer based on the:

  • Appearance of cancerous tissue examined under a microscope.
  • Location where the cancer began, either in the duct or the lobule.
  • Presence or absence of estrogen and progesterone hormone receptors on cancer cells.
  • Possible production of a cancer gene called the Human Epidermal Growth Factor Receptor-2 (HER2) oncogene.

Each of these types of breast cancer will present a different growth patterns, different abilities to spread beyond the breast and different disease outcomes. Learning your breast cancer type will help you to make appropriate choices about the best treatment options for you.

Luminal A

Luminal A breast cancers are slow-growing and low-grade, with cure rates that exceed 90 percent. Luminal A breast cancers represent approximately 35 percent of all types of breast cancers and are often discovered by screening mammography.

Luminal A breast cancer cells are similar to normal breast tissue cells and can remain in a single location without spreading into the lymph system or blood stream. Because Luminal A breast cancers are so slow-growing and unlikely to spread, there is a risk of overtreatment.

Luminal A breast cancers can generally be cured without chemotherapy, using limited surgery alone or in combination with radiation therapy. Left untreated, there is a possibility that Luminal A cancers can develop into Luminal B cancers.

Luminal B

Luminal B breast cancers grow more aggressively and quickly than Luminal A types. They are also more likely to spread beyond the breast to lymph nodes and blood vessels. Luminal B breast cancers represent approximately 30 percent of all types of breast cancers.

Unlike Luminal A cancers, which are situated in a specific site, Luminal B cancers can manifest in multiple sites within a particular region of the breast, with normal breast tissue existing in between. In these instances, mammography often underestimates the size of primary cancers and fails to detect secondary cancers. Magnetic resonance imaging (MRI) can help to more accurately measure and detect Luminal B cancers.

Treatments for Luminal B breast cancers can include limited surgery, mastectomy, radiation therapy and chemotherapy. However, recommended treatment options available to each woman will vary based on a range of personal factors regarding her disease and her risk factors.

Triple-Negative and Basal-Type

Basal-type cancers, of which approximately 90 percent are truly triple-negative, account for approximately 15 percent of all types of breast cancer. The term triple-negative, frequently used by the medical and patient communities, refers to the lack of hormone receptors on cancer cells and the absence of HER2 overproduction. The 10 percent of basal-type cancers that are not truly triple-negative do have some degree of hormone positivity.

Triple-negative cancers grow aggressively and quickly and do not respond to hormonal therapy. Approximately 90 percent of women with a BRCA1 gene mutation who develop breast cancer are affected by the triple-negative type. Triple-negative breast cancers are more prevalent in younger women and African-American women.

Triple-negative breast cancers are generally treated with a combination of surgery, radiation therapy and chemotherapy. While traditionally fairly poor, prognosis for triple-negative cancers is evolving as targeted therapies are being investigated.

HER2-Positive

HER2-positive cancers overproduce the HER2 oncogene and account for approximately 20 percent of all types of breast cancers. HER2-positive cancers are aggressive, grow rapidly, can spread easily and often result in recurrence.

Prognosis for HER2-positive cancers has been fairly poor, but developments in our understanding of the way HER2-positive cancer cells work have led to the development of targeted treatments that disrupt the interior pathways of HER2-positive cells causing them to die. For this reason, it is critical HER2-positive breast cancers are accurately diagnosed.