HR-positive, or hormone receptor-positive, refers to a characteristic of certain cancers, most notably breast cancer, where cancer cells possess specific proteins that can bind to hormones. These hormone receptors allow hormones like estrogen and progesterone to attach to the cancer cells. When hormones bind to these receptors, they can stimulate the cancer cells to grow and divide. Identifying a cancer as HR-positive is a significant factor in guiding treatment decisions, as it indicates that the cancer’s growth is influenced by hormones, allowing for targeted therapies.
The Role of Hormone Receptors
Hormone receptors are specialized proteins located on cells, designed to bind to specific hormones. In breast cancer, the primary hormone receptors are estrogen receptors (ER) and progesterone receptors (PR). These receptors normally play a role in regulating cell growth and function in healthy breast tissue.
When estrogen or progesterone hormones bind to their receptors on cancer cells, they signal the cells to multiply and the tumor to expand. Approximately 70% to 80% of breast cancers are classified as hormone receptor-positive, meaning they rely on these hormones for growth. Some cancers may be positive for both estrogen and progesterone receptors, while others may only have one type. This hormone dependence makes these cancers susceptible to therapies that block hormone action or reduce hormone levels.
Identifying HR Status
Determining a cancer’s hormone receptor (HR) status is a standard procedure performed after a biopsy or surgical removal of tumor tissue. A tissue sample is sent to a laboratory where specialized tests detect estrogen and progesterone receptors on the cancer cells.
The most common method for this analysis is immunohistochemistry (IHC). This laboratory technique uses antibodies that bind to hormone receptors, allowing pathologists to visualize and quantify their presence. If at least 1% of the tested cells show the presence of estrogen and/or progesterone receptors, the tumor is classified as hormone receptor-positive. This assessment provides information about how the cancer might respond to certain treatments.
Treatment Implications of HR-Positive Status
The HR-positive status of a cancer significantly influences treatment choice, as these cancers often respond well to hormone therapy, also known as endocrine therapy. This approach targets the cancer’s reliance on hormones for growth by blocking receptors or reducing the body’s hormone levels. Hormone therapy is a primary and highly effective treatment strategy for HR-positive cancers.
One common type of hormone therapy is selective estrogen receptor modulators (SERMs), such as tamoxifen. Tamoxifen works by binding to estrogen receptors on cancer cells, preventing estrogen from attaching and stimulating growth. SERMs can be used in both pre- and post-menopausal women.
Another class of drugs are aromatase inhibitors (AIs), such as anastrozole, letrozole, and exemestane. Aromatase inhibitors block the aromatase enzyme, which converts other hormones into estrogen in post-menopausal women.
By reducing overall estrogen levels, AIs limit the hormone available to fuel HR-positive cancer cell growth.
Hormone therapy can be administered for several years (often 5 to 10 years) after initial treatments like surgery or chemotherapy to help prevent cancer recurrence. This long-term approach helps suppress any remaining cancer cells. The effectiveness of hormone therapy for HR-positive cancers underscores the importance of accurately determining hormone receptor status for personalized treatment.