Understanding Breast Cancer Molecular Subtyping and Its Importance

Breast cancer is not a singular disease. There are several types, each with its own unique traits. These differences are based on the specific molecular makeup of each tumor, not just where it is or how much it has spread. Understanding these molecular differences is how oncologists make an accurate diagnosis, predict how the disease might progress, and, most importantly, create a personalized treatment plan that specifically targets each type of breast cancer.

Learn about the molecular subtyping that guides oncologists in using the most appropriate treatments and gives them an idea of the chances of survival and recovery.

Molecular Subtyping of Breast Cancer

Molecular subtypes classify breast cancer based on specific traits, such as hormone receptors and proteins, which influence breast cancer growth.

There are four main molecular subtypes of breast cancer:

• Luminal A

• Luminal B

• HER2-positive

• Triple-negative

Luminal A Breast Cancer

Luminal A breast cancer is the most common subtype and is often referred to as hormone receptor-positive and HER2-negative (HR+/HER2-). This subtype is estrogen receptor-positive and progesterone receptor-positive but lacks the HER2 protein that promotes cancer growth. Luminal A is typically slow-growing and has a good prognosis due to having low levels of the Ki-67 protein, which can fuel cancer growth.

Luminal B Breast Cancer

Luminal B breast cancer is hormone receptor-positive and HER2-positive (HR+/HER2+), which is sometimes referred to as triple-positive breast cancer. Patients with Luminal B breast cancer often have higher levels of the Ki67 protein, resulting in more aggressive tumor growth compared to Luminal A.

While Luminal B cancers may have progesterone receptors, they are primarily estrogen-positive. Compared to Luminal A, it tends to have a higher likelihood of recurrence and is associated with a poorer prognosis due to larger tumor sizes and faster growth rates. Nevertheless, luminal B breast cancer still has a relatively high survival rate.

HER2-Positive/HER2-Enriched Breast Cancer

HER2-enriched breast cancer expresses the HER2 protein and may or may not be hormone-receptor positive. Generally, HER2-positive breast cancers grow more quickly and aggressively than Luminal A. This often leads to a less favorable prognosis. However, recent advancements in treatments for HER2-positive breast cancer are helping improve outcomes for patients diagnosed with this subtype.

Triple-Negative Breast Cancer (TNBC)

A lack of receptors for estrogen, progesterone, and HER2 characterizes triple-negative breast cancer. This subtype typically starts in the breast ducts and is known for its aggressive nature, which often results in poorer outcomes compared to other breast cancer types.

How Molecular Subtyping Affects Breast Cancer Treatment

Breast cancer doctors customize breast cancer treatment plans based on the molecular subtype. This allows each patient to receive cancer care tailored to the specific breast cancer’s characteristics.

Treatments for Breast Cancer Subtypes

Most breast cancer patients undergo surgery as part of treatment. Chemotherapy and radiation therapy may also be used for all types of breast cancer. Additional treatments are determined by the cancer's molecular subtype, stage, and lymph node involvement.

Standard treatment approaches based on breast cancer molecular subtypes include:

• Luminal A Breast Cancer: Hormone therapy is typically recommended, as hormones drive this subtype. These medications work by lowering progesterone and/or estrogen levels to slow cancer progression. Hormone therapy may also be used to prevent cancer recurrence.

• Luminal B Breast Cancer: Since this subtype is influenced by both hormones and an overgrowth of HER2 protein, treatment plans usually include hormone therapies and targeted therapies to counteract both.

• HER2-Positive Breast Cancer: Targeted therapies, such as monoclonal antibodies, can effectively attack HER2-positive cells to halt their growth.

• Triple-Negative Breast Cancer: As TNBC does not have receptors for estrogen, progesterone, and HER2, it cannot be treated with hormone therapies. Instead, treatment typically consists of chemotherapy, immunotherapy, and radiation therapy. If the cancer has not spread, surgery is likely part of the treatment plan.

Hormone Therapies for Breast Cancer

Hormone therapy is used to treat hormone receptor-positive breast cancer by reducing or blocking estrogen, which drives tumor growth. This approach can shrink tumors before surgery, slow the progression of advanced cancer, and lower the risk of recurrence.

Commonly used hormone therapies include:

• Aromatase inhibitors: These medicines decrease estrogen production (e.g., anastrozole, exemestane, letrozole).

• Selective Estrogen Receptor Modulators (SERMs): SERMs block estrogen in specific cells (e.g., tamoxifen, toremifene, raloxifene).

• Selective Estrogen Receptor Downregulators (SERDs): These drugs prevent estrogen from acting on cells (e.g., elacestrant, fulvestrant).

Women with early-stage breast cancer typically undergo hormone therapy for five years. The treatment regimen may consist of tamoxifen or a combination of tamoxifen and aromatase inhibitors, depending on whether the patient is pre- or post-menopausal. Recent breast cancer research indicates that taking tamoxifen for ten years instead of five can reduce the risk of cancer recurrence and improve survival rates in some cases.

Post-menopausal women with cancer in the lymph nodes (node-positive) may continue hormone therapy, particularly aromatase inhibitors, for up to ten years after surgery.

Targeted Therapies for Breast Cancer

Targeted therapy focuses on attacking specific cancer cells while minimizing harm to normal cells. Some examples of targeted therapies commonly used for breast cancer include:

• Trastuzumab: A HER2-targeted therapy

• Pertuzumab: Another HER2-targeted therapy

• Everolimus: A targeted therapy that can be used for hormone-positive patients or those with triple-negative breast cancer.

Personalized Breast Cancer Treatment in the South Chicago Suburbs

The breast cancer doctors at Affiliated Oncologists provide the most advanced cancer care and personalized treatments based on the cancer’s molecular subtypes.

If you or a loved one was diagnosed with a type of breast cancer and is seeking treatment in the South Chicago suburbs, the oncologists at Affiliated Oncologists are here to support you every step of the way. We serve the suburbs south of Chicago, including Chicago Ridge, Hazel Crest, Mokena, Orland Park, and Palos Heights, ensuring convenient access to cancer treatments for local residents.

Categories: Breast Cancer