An ER-positive cancer diagnosis indicates that the cancer cells possess specific proteins called estrogen receptors (ER). These receptors allow the hormone estrogen to bind to the cancer cells, which can then stimulate their growth and proliferation. Approximately 80% of breast cancers are classified as ER-positive, making it the most common subtype. This characteristic is a significant factor in determining the most effective treatment strategies for individuals with this type of cancer.
The Role of Estrogen in Cancer Growth
Estrogen, a naturally occurring hormone in the body, plays a role in the normal growth and development of cells, particularly in breast tissue. In healthy cells, estrogen binds to estrogen receptors, acting like a “key” fitting into a “lock” on the cell surface or inside the cell. This interaction triggers a series of signals that instruct the cell to divide and multiply, a controlled and regulated process.
In the context of ER-positive cancer, however, this normal signaling becomes uncontrolled. When estrogen binds to the abundant receptors on cancer cells, it fuels their division and growth, leading to tumor progression. Cancer cells are also often tested for progesterone receptors (PR), as progesterone can similarly promote tumor growth. About 65% of ER-positive breast cancers are also PR-positive, indicating that both hormones may contribute to their proliferation.
Diagnosis and Testing Procedures
The diagnosis of ER-positive cancer begins with obtaining a tissue sample, typically through a biopsy of the tumor. This sample is then sent to a pathology laboratory for specialized testing. The primary method used to identify estrogen receptors is called immunohistochemistry (IHC).
During an IHC test, specific antibodies are applied to the tissue sample, which bind to the estrogen receptors on the cancer cells. A chemical reaction causes a visible stain, allowing a pathologist to observe the receptors under a microscope. A cancer is considered ER-positive if 1% or more of the tumor cells show positive nuclear staining for estrogen receptors. Pathology reports may also indicate a percentage, such as “90% ER positive,” reflecting the proportion of cells expressing these receptors.
Targeted Treatment Approaches
Treatment for ER-positive cancer often involves hormone (endocrine) therapies, which are designed to counteract estrogen’s effects on cancer cells. These therapies work either by blocking estrogen receptors or by reducing the overall amount of estrogen in the body. The specific approach depends on factors such as menopausal status and disease stage.
Selective Estrogen Receptor Modulators (SERMs)
Selective Estrogen Receptor Modulators (SERMs), like tamoxifen, are drugs that directly interact with estrogen receptors. Tamoxifen binds to estrogen receptors on breast cancer cells, blocking estrogen from attaching. This prevents cancer cells from receiving signals to divide and multiply. Tamoxifen can be used in both premenopausal and postmenopausal women.
Aromatase Inhibitors (AIs)
Aromatase Inhibitors (AIs), such as letrozole, anastrozole, and exemestane, reduce estrogen production by blocking the enzyme aromatase. Aromatase converts other hormones, called androgens, into estrogen, primarily in peripheral tissues like fat and muscle after menopause. By inhibiting this enzyme, AIs significantly lower estrogen levels, starving ER-positive cancer cells of the hormone they require for growth. AIs are prescribed for postmenopausal women, as their ovaries no longer produce the majority of the body’s estrogen.
Other Therapies
For premenopausal women, ovarian suppression is another treatment option. This approach involves temporarily or permanently stopping the ovaries from producing estrogen, often through medication or surgical removal. Reducing ovarian estrogen production diminishes the hormone available to fuel ER-positive cancer cells. CDK4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, may also be used for advanced ER-positive breast cancers in combination with hormone therapy. These drugs target specific proteins that regulate cell division, hindering cancer cell proliferation.
Prognosis and Recurrence Factors
An ER-positive diagnosis offers a more favorable prognosis compared to ER-negative cancers because effective targeted hormone therapies are available. These treatments reduce the risk of cancer recurrence and improve long-term survival rates. Over 90% of females diagnosed with breast cancer are alive five years after diagnosis, with hormone receptor-positive cancers associated with better survival chances.
A unique characteristic of ER-positive cancers is the risk of late recurrence, which can occur more than five years after initial diagnosis. For some individuals, the risk of recurrence can even be higher after five years than in the initial period following treatment. This sustained risk explains why hormone therapy is often recommended for an extended duration, sometimes for 7 to 10 years, to continue suppressing potential cancer cell growth. Factors influencing this late recurrence risk include the initial tumor size, the number of lymph nodes involved, and the tumor’s grade.