Breast Cancer and Hormones
Estrogen receptors (ER) and progesterone receptors (PR)

In addition to playing a role in essential biological functions, the female hormones estrogen and progesterone can also help to fuel the growth of certain types of breast cancer tumors. While not all malignant breast tumors are affected by estrogen or progesterone, tumors that are found to contain receptors (how proteins and hormones attach to cells) for estrogen and progesterone are referred to as estrogen positive (ER+) or progesterone positive (PR+).

Tumors are usually checked for hormone receptors either after biopsy or lumpectomy, or following surgical removal. An estimated two out of three tumors are believed to be either ER+ or PR+, and are most commonly found in older patients.

HER2

HER2 is a protein that promotes excessive cell growth by instructing the cells to continually replicate copies of the protein, or the HER2 gene itself. According to the American Cancer Society, approximately one in five invasive cancerous breast tumors are found to be HER2 positive (HER2-positive).

HER2 Cancer Types

HER2 positive – This type of tumor has either too much of the HER2 protein, or too many copies of the HER2 gene, and can be treated with HER2 targeting medication.

Triple-positive – A triple positive tumor is found to be ER+ (estrogen receptor), PR+ (progesterone receptor), as well as HER2 positive. Triple positive tumors are also treated with hormone and HER2 targeting drugs.

HER2 negative – Tumors that do not have excessive levels of HER2 proteins or copies of the gene are labeled HER2 negative, and therefore do not respond to HER2 targeting drugs.

Triple-negative – This type of tumor is negative for estrogen and progesterone receptors, and does not contain excessive copies of the HER2 gene or protein. This type of tumor tends to grow and spread more quickly, and does not respond to hormone specific drugs.

DNA Testing in Cancer Cells

Understanding the rate at which cells divide can help to determine how aggressive and fast growing a cancerous breast tumor might be. A Ki-67 test can measure the rate of cancer cell division, with a more rapid rate of division (higher Ki67%) indicating a more aggressive tumor.

Breast Cancer and Genes

Thanks to heightened awareness and the availability of genetic testing, most women know that carrying certain genes, such as the BRCA1 and BRCA2 genes, can increase the risk of developing breast cancer.

In addition to classifying malignant breast tumors by their composition when observed under a microscopic, further classifications are being established to account for the expression of certain genetic traits, in order to better understand how the tumors grow and behave, with the aim of developing more targeted and effective treatment options.

Along with HER2, there are currently three other categories for breast tumors, including:

Luminal A and Luminal B tumors – Both Luminal A and B tumors are estrogen receptor positive. They resemble the normal cell growth patterns found inside the lumen of the breasts (inside of the breast duct or gland). Luminal A tumors are usually slower growing and of a lower grade. Luminal B tumors tend to grow faster than Luminal A.

Basal – Basal tumors are triple negative and adhere to the genetic expression of the deep basal cell layers of the breasts. Most common in younger, Hispanic, and African American women, basal tumors are usually highly aggressive and fast growing. This type of tumor is common in women with the BRCA1 gene mutation.