Types of Breast Cancer
Invasive Breast Cancer
An invasive (sometimes referred to as infiltrating) cancer is one that has gotten out of the duct or lobule. Since lobules and ducts are kinds of glands and the medical term meaning “related to a gland” is adeno, sometimes these cancers are called “adenocarcinomas.” People can be confused by this term, thinking it’s a different kind of cancer. In reality, it’s just a broader category—like calling someone from Los Angeles a Californian.
An infiltrating ductal cancer forms a hard, firm lump. The lump forms because the neighborhood or surrounding tissue causes scar tissue (fibrosis) around the cells. Infiltrating lobular cancer, on the other hand, is sneaky. It sends individual cells in little fingerlike projections (cells extending in a line, single file) out into the tissues, so you may feel it as a little thickening rather than a hard lump or you may not feel it at all. Because lobular cancers elicit less scarring, they tend to grow to larger sizes (average five cm) than ductal carcinoma (average two cm) before they are detected. The prognosis is based on size, and type, of cancer. Infiltrating lobular cancers are almost always sensitive to hormones and seem to be more common in women who have taken hormone replacement therapy. In addition, there’s a slightly higher tendency for lobular cancer to occur in the other breast at a later time.
You can learn more about how breast cancer develops in Breast Cancer 101.
We used to think there was just one type of breast cancer. Now we know that’s not the case. There are different breast cancer subtypes, and the pathologist will determine which subtype you have by looking for specific molecular markers in the cancer cell. The markers are classified into three categories:
- ones that are used to help determine the prognosis of a particular cancer (how life-threatening it is),
- ones that are used to predict that a cancer will respond to a certain treatment, and
- ones that do both.
By classifying your tumor by these molecular markers, the pathologist is also giving you and your doctor information that will be used to determine the best treatment options.
You can learn more about making breast cancer treatment decisions for your type of breast cancer in Impatient Science.
Types of Invasive Breast Cancer
All breast tumors are tested to see if they have estrogen receptors and whether they are HER2-positive. Your tumor may also be tested for other genetic mutations if you are considering a clinical trial. In addition to learning the type of tumor you have, your doctors will discuss the tumor’s stage, a measure of how far it has spread.
This information will help you understand what you will learn or may have already been told.
Estrogen and Progesterone Receptors
Breast tumors are tested to see if they are estrogen receptors (ER) and/or progesterone receptor (PR) positive or negative. Hormone receptor tests are both prognostic and predictive. In general, tumors that are ER+ and/or PR+ are slightly slower growing and have a slightly better prognosis than tumors that aren’t. The test also provides information about treatment options. If your tumor is ER+ and/or PR+, then your cancer can be treated with a hormone therapy. Tumors that are ER- and PR- do not respond to hormone therapies. This is not a “negative” or “bad” thing because they but do respond well to chemotherapy and/or targeted therapies.
Learn more in our section on ER+/Hormone-Sensitive Tumors.
Breast tumors are also tested to see if they overexpress (have too many copies of) the Her-2/neu (also known as erb-b2) oncogene. Her-2/neu (typically referred to as HER2) is one of the dominant oncogenes that contributes to cancer by telling cells to grow. Instead of being mutated, however, Her-2/neu is frequently overexpressed and amplified: in other words, there are too many copies of the oncogene so the intensity of the message telling the cells to grow is increased. The HER2 test is both prognostic and predictive. HER2+ tumors tend to be more aggressive but can be treated with a HER2-targeted therapy.
Learn more in our section on HER2+ Tumors.
Triple Negative Breast Cancer
Instead of describing a tumor as ER-negative, PR-negative, and HER2-negative we use the shorthand term “triple negative.” Studies show that African-American women appear more likely to develop triple-negative tumors than women of other ethnic backgrounds. Women who carry a BRCA1 mutation are also more likely to develop triple-negative tumors. We don’t yet know the biological reasons for this, but scientists are studying African-American women and women with BRCA1 mutations in an attempt to learn why.
Learn more in our section on Triple Negative Breast Cancer.
Inflammatory Breast Cancer
Inflammatory breast cancer (IBC) is a serious kind of advanced breast cancer. IBC accounts for about one to five percent of all breast cancer cases in the U.S. each year. IBC has a different phenotype, which means it looks and acts differently than other forms of breast cancer. It rarely appears as a lump. Instead, symptoms typically include a swelling or redness that affect a third or more of the breast. The skin may have ridges or appear pitted, like the skin of an orange (called peau d’orange). These symptoms develop because cancer cells have blocked lymph vessels in the skin, preventing the normal flow of lymph through the tissue. Inflammatory breast cancer progresses rapidly, and at diagnosis is either stage III (the cancer has spread to nearby lymph nodes) or stage IV (the cancer has spread to other organs).
Learn more in our section on inflammatory breast cancer.
The cancer staging system was developed before we had the molecular markers we now use to identify tumor types. The system combines the microscopic aspects of the tumor that the pathology report addresses with clinical features of the tumor in a staging system. This classification system, known as the TNM (short for tumor, nodes, and metastasis), categorizes cases so we can keep statistics and determine likely long-term survival rates that various treatments can create.
The system is still used, but it is actually a holdover from the past. It doesn’t fit very well with our current knowledge of biology because it is based only on the size of the tumor in the breast, the number of lymph nodes involved, and clinically detected spread to other organs.
The American Society for Clinical Oncology provides an extensive patient-friendly explanation with images for the TNM system here.
The TNM system is used to determine the cancer’s stage. The broad categories of the staging system are:
- Stage I: A small tumor that has not spread to the lymph nodes.
- Stage II: Either a small tumor with positive lymph nodes or a tumor between two and five centimeters with negative lymph nodes.
- Stage III: A large tumor with positive lymph nodes and which may have spread to the chest wall.
- Stage IV: A tumor that has spread (metastasized) to other organs in the body.
Your cancer’s stage will also play a role in determining how your cancer is treated.
Learn more in Treatment Options.