Endocrine therapy, sometimes referred to as hormone therapy, is a treatment approach for breast cancers that exhibit sensitivity to hormones. This therapy works by targeting specific pathways that cancer cells use to grow and multiply, aiming to slow or halt their progression.
How Endocrine Therapy Works on Cancer Cells
Breast cancer cells often possess specialized proteins called hormone receptors (HRs) on their surface, specific for estrogen (ER-positive) or progesterone (PR-positive). When hormones like estrogen or progesterone bind to these receptors, they signal the cancer cell to grow and divide. Endocrine therapy aims to disrupt this growth-promoting signal. The treatment either prevents hormones from binding to their receptors or reduces the amount of hormones available to the cancer cells. This effectively removes the fuel for hormone-sensitive cancer cells. The therapy is applicable only to breast cancers that test positive for these hormone receptors, indicating their reliance on hormones for growth.
Types of Endocrine Therapy Drugs
Different classes of endocrine therapy drugs work through distinct mechanisms to target hormone-sensitive breast cancer. These medications interrupt estrogen-driven cancer growth by blocking its effects or reducing its production. Each type is suited for specific patient profiles based on menopausal status and cancer characteristics.
Selective Estrogen Receptor Modulators (SERMs)
Selective Estrogen Receptor Modulators (SERMs) act by blocking estrogen from binding to receptors on breast cancer cells. Tamoxifen is a widely used example of a SERM, and it can be prescribed for both premenopausal and postmenopausal women. While it blocks estrogen in breast tissue, Tamoxifen can act like estrogen in other parts of the body, such as the uterus and bones.
Aromatase Inhibitors (AIs)
Aromatase Inhibitors (AIs) stop the body from producing estrogen in fat tissue, which is the main source of estrogen in postmenopausal women. Drugs in this class include Anastrozole, Letrozole, and Exemestane. Because they target estrogen production outside the ovaries, AIs are typically prescribed only for women who have gone through menopause.
Ovarian Suppression
Ovarian suppression is an approach primarily used for premenopausal women to reduce estrogen levels by halting the ovaries’ production of the hormone. This can be achieved temporarily through medication, such as GnRH agonists like Goserelin, which suppress ovarian function. Alternatively, ovarian suppression can be permanent through surgical removal of the ovaries. This method is often combined with an AI or Tamoxifen to enhance treatment effectiveness.
Selective Estrogen Receptor Degraders (SERDs)
Selective Estrogen Receptor Degraders (SERDs) block estrogen receptors and cause their degradation. Fulvestrant, an example that is administered by injection, is generally used for advanced breast cancer, particularly when other endocrine therapies are no longer effective.
The Treatment Process and Duration
Endocrine therapy is incorporated into breast cancer treatment plans in several clinical settings, depending on the stage and characteristics of the cancer. It is used as adjuvant therapy, given after primary treatments such as surgery, chemotherapy, or radiation, to reduce the chance of the cancer returning by targeting any remaining microscopic cancer cells. The therapy can also be administered as neoadjuvant therapy before surgery to shrink a tumor, potentially making it smaller and easier to remove. This pre-surgical approach may allow for a less extensive operation, preserving more healthy tissue. For individuals with metastatic breast cancer, endocrine therapy is used to slow or stop the growth of the widespread disease, helping manage symptoms and improve quality of life.
The typical duration of endocrine therapy for early-stage breast cancer is 5 to 10 years to maximize the reduction in recurrence risk. For advanced or metastatic cancer, treatment may continue for as long as the therapy remains effective in controlling the disease.
Common Side Effects of Treatment
The side effects associated with endocrine therapy largely stem from the reduction of estrogen in the body, mimicking symptoms typically experienced during menopause. Common effects include hot flashes, night sweats, vaginal dryness, and musculoskeletal issues like joint pain and stiffness. Changes in bone health are a notable concern, especially with Aromatase Inhibitors, as these drugs can lead to a decrease in bone density and an increased risk of osteoporosis over time.
While generally well-tolerated, Tamoxifen carries specific, though less common, risks. These include an elevated risk of developing blood clots in the legs or lungs. There is also a small increased risk of uterine cancer with Tamoxifen use, so any unusual vaginal bleeding or spotting should be reported to a healthcare provider.