Metastatic breast cancer (mBC) is an advanced stage of breast cancer where the disease has spread from the breast to other parts of the body.

Understanding HR+/HER2- Metastatic Breast Cancer (mBC)

Metastatic breast cancer (mBC) is an advanced stage of breast cancer where the disease has spread from the breast to other parts of the body, such as the bones, lungs, liver, or brain. Among the various subtypes of mBC, Hormone Receptor Positive (HR+) and HER2 Negative (HER2-) is the most common. Understanding this specific type is crucial for patients, caregivers, and healthcare professionals alike, as it dictates the most effective treatment strategies.

What is HR+/HER2- Metastatic Breast Cancer?

This subtype is defined by the presence of hormone receptors (HR+) and the absence of HER2 protein overexpression (HER2-). These characteristics are determined through pathology tests on breast tissue samples and play a fundamental role in guiding therapeutic decisions.

Hormone Receptor Positive (HR+)

Breast cancer cells are considered HR+ if they have receptors for estrogen (ER+) or progesterone (PR+), or both. These hormones can fuel the growth of cancer cells. Approximately 70-80% of all breast cancers are hormone receptor positive. This characteristic makes endocrine (hormone) therapy a cornerstone of treatment for HR+ breast cancers, including those that are metastatic.

HER2 Negative (HER2-)

HER2 stands for Human Epidermal growth factor Receptor 2. It is a protein found on the surface of some breast cancer cells that can promote cell growth. HER2 negative means that the cancer cells do not overexpress or have amplified levels of the HER2 protein. This indicates that treatments specifically targeting HER2, such as trastuzumab or pertuzumab, are not effective for this subtype.

Diagnosis and Staging of HR+/HER2- mBC

Diagnosis of mBC typically involves a combination of imaging tests (such as CT scans, bone scans, PET scans, or MRI) and biopsies of suspected metastatic sites. Once confirmed, mBC is classified as Stage IV breast cancer. The HR+/HER2- status is re-evaluated at the time of metastasis, as receptor status can sometimes change over time or in different tumor sites.

Treatment Approaches for HR+/HER2- mBC

Treatment for HR+/HER2- mBC focuses on managing the disease, controlling symptoms, and improving quality of life, as it is generally considered a chronic, treatable condition rather than curable. Treatment plans are highly individualized and depend on various factors, including previous treatments, site of metastasis, tumor burden, and patient overall health.

Endocrine (Hormone) Therapy

This is often the first-line treatment for HR+/HER2- mBC. It works by blocking hormones from reaching cancer cells or by lowering hormone levels in the body. Common types include:

• Aromatase Inhibitors (AIs): Such as anastrozole, letrozole, and exemestane, which are typically used in postmenopausal women to reduce estrogen production.


• Selective Estrogen Receptor Modulators (SERMs): Like tamoxifen, which blocks estrogen receptors on cancer cells. Can be used in both pre- and postmenopausal women.


• Selective Estrogen Receptor Degraders (SERDs): Such as fulvestrant, which degrades the estrogen receptor.

Targeted Therapies

These drugs specifically target pathways involved in cancer cell growth and survival. They are often used in combination with endocrine therapy to enhance effectiveness and delay resistance.

• CDK4/6 Inhibitors: Drugs like palbociclib, ribociclib, and abemaciclib are commonly used alongside endocrine therapy. They block proteins (CDK4 and CDK6) that promote cancer cell division, significantly improving progression-free survival for many patients.


• mTOR Inhibitors: Everolimus is an example that can be used in combination with an AI after progression on other endocrine therapies.


• PI3K Inhibitors: Alpelisib is an example used for patients with a PIK3CA mutation, in combination with fulvestrant.

Chemotherapy

While endocrine and targeted therapies are usually preferred due to fewer side effects, chemotherapy may be used in certain situations. This includes cases where the cancer is progressing rapidly, hormone therapy is no longer effective, or there is significant organ involvement (visceral crisis).

Other Supportive Therapies

Managing symptoms and side effects is a crucial part of living with mBC. This can include pain management, bone-modifying agents to strengthen bones and prevent fractures if the cancer has spread to the bones, and supportive care for other treatment-related side effects.

Living with HR+/HER2- mBC

Living with HR+/HER2- mBC means navigating a chronic illness that requires ongoing management. Patients often work closely with a multidisciplinary team, including oncologists, nurses, social workers, and palliative care specialists, to ensure comprehensive care. Maintaining open communication with the healthcare team, understanding treatment goals, and actively participating in shared decision-making are vital aspects of managing the disease and maintaining the best possible quality of life.