Breast Cancer Subtypes Based on Biomarkers
In addition to identifying where a breast cancer began and how it grows, pathologists test the cancer cells for specific biomarkers that can influence treatment. The most important routinely tested biomarkers include estrogen receptor (ER), progesterone receptor (PR) and HER2.
These biomarker results describe the biology of the cancer and are considered together with its histologic type. For example, an invasive ductal or invasive lobular carcinoma may also be hormone receptor-positive, HER2-positive or triple-negative. Some breast cancers have more than one biomarker characteristic.
Hormone Receptor-Positive Breast Cancer
Hormone receptor-positive breast cancer has estrogen receptors, progesterone receptors or both on the cancer cells. These receptors allow hormones in the body to influence the growth of the cancer.
Because the cancer cells depend in part on hormone signaling, endocrine therapy can often be used to block this pathway or reduce the amount of hormone available to the tumor. Hormone receptor status is considered together with the cancer’s stage, grade, HER2 status and other clinical findings when treatment is planned.
HER2-Positive Breast Cancer
HER2-positive breast cancer has increased amounts of the HER2 protein or additional copies of the HER2 gene. HER2 plays a role in cell growth, and increased HER2 signaling can cause cancer cells to grow and divide more rapidly.
Identifying HER2-positive disease is important because treatments that specifically target HER2 can be highly effective for appropriate patients. A breast cancer can be HER2-positive whether it is hormone receptor-positive or hormone receptor-negative, so both sets of biomarkers are evaluated when the tumor is classified.
Triple-Negative Breast Cancer
Triple-negative breast cancer does not have estrogen receptors or progesterone receptors and does not have the HER2 characteristics that define HER2-positive disease. Because these three common treatment targets are absent, endocrine therapy and HER2-targeted therapy are not effective against triple-negative breast cancer.
Triple-negative breast cancers often grow more quickly than many hormone receptor-positive breast cancers and may have a greater likelihood of recurrence during the first several years after diagnosis. Treatment depends on the stage and characteristics of the cancer and may include chemotherapy, immunotherapy, surgery, radiation therapy or other treatments when appropriate.
Why Biomarker Subtype Matters
Biomarker results help identify treatments that are more likely to work against a particular breast cancer. They are interpreted together with the histologic type, tumor grade, stage, lymph node involvement and other findings rather than being used alone to determine prognosis or treatment.
Biomarker status can also change in some breast cancers over time or after recurrence, which is one reason additional tissue testing may occasionally be recommended if the cancer returns or spreads.
Learn more about how tumor biology helps guide surgery, systemic therapy and radiation treatment. See Breast Cancer Treatment.
Special Clinical Forms and Extent of Breast Cancer
Some breast cancers are described not only by where they begin or which biomarkers they express, but also by the way they involve the breast or whether they have spread beyond it. Inflammatory breast cancer and metastatic breast cancer are important examples because they describe different clinical patterns and stages of disease rather than a separate histologic type.
Inflammatory Breast Cancer
Inflammatory breast cancer is a rare and aggressive form of invasive breast cancer in which cancer cells block lymphatic vessels in the skin of the breast. This can cause rapid swelling, redness, warmth, heaviness or thickening of the breast, often without a clearly defined mass.
The skin may develop dimpling or a pitted appearance sometimes described as resembling the surface of an orange. Because these changes can resemble infection or inflammation, persistent or rapidly progressing symptoms should be evaluated promptly so the correct diagnosis can be established.
Metastatic Breast Cancer
Metastatic breast cancer, also called stage IV breast cancer, occurs when breast cancer cells have spread beyond the breast and nearby lymph nodes to distant parts of the body. Common sites include the bones, lungs, liver and brain.
Even when breast cancer spreads to another organ, it remains breast cancer because the cancer cells retain the characteristics of the original breast tumor. Treatment is based on the biology of the breast cancer, the locations involved, prior treatment and the patient’s overall health and goals of care.
Metastatic breast cancer is generally considered treatable rather than curable, and treatment may help control the cancer, relieve symptoms and support quality of life for extended periods of time.
How Breast Cancer Develops and Spreads
Breast cancer begins when changes within breast cells disrupt the normal controls on cell growth and division. These changes can occur over time and may be influenced by inherited genetic factors, hormones, age, environmental exposures and other factors, although the exact cause of an individual breast cancer often cannot be identified.
Some abnormal breast cells remain confined within the structure where they began. For example, ductal carcinoma in situ remains inside a milk duct and has not invaded the surrounding breast tissue. Invasive breast cancer develops when cancer cells grow beyond that boundary and into nearby breast tissue.
Invasion and metastasis describe different processes. Invasion means cancer cells have grown into surrounding breast tissue. Metastasis means cancer cells have traveled through the lymphatic system or bloodstream and established cancer in another part of the body.
Not every breast cancer follows the same course or progresses at the same rate. Tumor type, grade, stage and biomarker profile all provide information about how the cancer may behave and help guide treatment decisions.
Learn more about how these findings are used to define an individual breast cancer. See Breast Cancer.
How Breast Cancer Type Affects Treatment
Breast cancer treatment is not determined by one feature alone. The care team considers the histologic type of cancer, biomarker subtype, tumor grade, stage, lymph node involvement and other clinical findings together when recommending treatment.
Matching Treatment to the Cancer
Some breast cancers are more likely to respond to specific treatments because of their biology. Hormone receptor-positive cancers may respond to endocrine therapy, HER2-positive cancers may respond to HER2-targeted treatment, and triple-negative breast cancers may be treated with chemotherapy, immunotherapy or other systemic treatments depending on the stage and clinical situation.
Surgery and radiation therapy may also be important parts of treatment, depending on the location and extent of the cancer. The sequence of treatment can vary, and some patients may receive medication before surgery while others begin with surgery.
Treatment Decisions Are Individualized
Two patients with the same general type of breast cancer may receive different treatment recommendations because their cancers differ in size, stage, biomarkers, lymph node involvement or other features. Age, overall health, prior treatment and personal preferences may also influence the treatment plan.
For this reason, breast cancer type is best understood as one part of a larger clinical picture rather than as a single predictor of treatment or outcome.
Learn more about how surgery, radiation therapy and systemic treatments may be combined based on the characteristics of the cancer. See Breast Cancer Treatment.
Moving Forward With a Breast Cancer Diagnosis
Understanding the type and subtype of breast cancer can make the diagnosis easier to interpret and help explain why certain treatments are recommended. These details are considered together with the stage, grade and other clinical findings to build a complete picture of the cancer.
At the Margie Petersen Breast Center, our multidisciplinary breast team works together to review these findings and develop a treatment plan based on the biology and extent of the cancer, as well as the individual needs and preferences of each patient.
Talk With Our Breast Clinic Team
The Breast Health Clinic can be reached at (310) 582-7209. If you have questions about a new breast symptom, need an evaluation or would like help determining your next step, call and a member of our team can assist you.
