Types of Targeted Therapy Drugs for Breast Cancer

Did you know that even six months after chemotherapy, 97.4% of patients still experience at least one side effect? How about that 66.7% of patients endure over six different side effects from chemo, and that radiation exposure increases the rate of secondary cancers by 58% in women and 35% in men?

In response to the growing concerns about conventional cancer treatments, researchers have introduced precision oncology as a safer, more targeted alternative. Although these therapies can also have side effects, they are mostly mild, manageable, and temporary. More serious side effects rarely occur.

Here’s everything you need to know about targeted therapies for breast cancer and the future of medical oncology.

 

What Is Targeted Therapy for Breast Cancer?

Unlike traditional therapies, precision oncology (the general term for targeted therapy) zeroes in on specific molecules or pathways in cancer cells. It blocks cancerous organisms from growing and spreading without affecting most of the surrounding healthy tissue—one of the reasons why cancer patients hesitate to get chemo and radiotherapy.

 

How Does Targeted Therapy Differ from Traditional Chemotherapy and Radiation?

Chemotherapy and radiation attack all rapidly dividing cells, including healthy cells. Targeted therapy is selective and precise.

Chemotherapy, for example, affects cells throughout the body, causing side effects like fatigue, diarrhea, and dyspnea to persist long after treatment ends. Also, thanks to inaccurate depictions in movies and television shows, a common misconception is that cancer itself causes hair loss. In reality, most hair loss happens because high-dose chemotherapy kills hair follicles and makes the hair fall out.

In contrast, targeted therapy seeks out only the cancer cells, reducing damage to surrounding tissue and resulting in fewer, short-term side effects. This precision and personalization makes targeted therapy particularly useful for complex cancers that no longer respond to conventional treatments, as it allows for interventions tailored to each patient and their cancer’s biological makeup.

 

Common Types of Breast Cancer Targeted

Breast cancer is not one disease but a group of cancers with different biological profiles. Each subtype responds differently to treatments, and targeted therapies work best when matched to the specific type of breast cancer they’re designed for.

 

Hormone Receptor-Positive Breast Cancer

This subtype includes cancers that grow in response to estrogen or progesterone. Targeted therapies for hormone receptor-positive cancers often involve blocking hormone receptors to prevent the cancer cells from receiving growth signals.

 

HER2-Positive Breast Cancer

HER2-positive cancers have too many HER2 proteins on their cell surfaces, which fuels rapid growth. Targeted therapies for HER2-positive breast cancer obstruct these proteins to slow or cease cancer from evolving and metastasizing.

 

Triple-Negative Breast Cancer (TNBC)

TNBC is one of the more challenging types to treat. It lacks estrogen, progesterone, and HER2 receptors, which makes it resistant to traditional hormone therapies. Although aggressive, newer targeted therapies and immunotherapy strategies are molding a brighter future for TNBC patients.

 

Types of Targeted Therapy

For transparency, this article includes the common and rare side effects associated with these therapies. Keep in mind that unlike traditional chemotherapy and radiation exposure, where side effects are often unavoidable, experienced healthcare providers meticulously supervise targeted therapies to adjust doses and minimize the risk of severe reactions.

An oncologist may recommend the following treatment options depending on the type of breast cancer:

 

1. Hormone Therapy (Endorcine Therapy)

Hormone therapy is a common form of targeted treatment for breast cancer, especially if the malignancy is hormone receptor-positive. Many breast cancers grow in response to hormones like estrogen and progesterone. Blocking these hormones or reducing their levels can delay or halt cancer progression.

 

Types of Hormone Therapy for Breast Cancer

Each of the following work in different ways to block or lower hormone levels:

  • Selective Estrogen Receptor Modulators (SERMs): SERMs cling to estrogen receptors on breast cancer cells and prevent the hormone from binding and stimulating cancer growth. Falling into this category are drugs like Tamoxifen, which oncologists prescribe for premenopausal and postmenopausal women with ER+ breast cancer. These meds are also effective on male patients, as 90% of male breast cancer cases express the ER.
  • Aromatase Inhibitors (AIs): These drugs block the enzyme aromatase, which the body uses to produce estrogen, particularly in postmenopausal women. By lowering estrogen levels, these medications limit the hormone available to feed malignant cells, helping to slow down or cease growth. Drugs like Anastrozole (Arimidex), Letrozole (Femara), and Exemestane (Aromasin) belong to this group.
  • Selective Estrogen Receptor Degraders (SERDs): An example of a SERD is Fulvestrant (Faslodex), which impedes estrogen receptors and degrades them. SERDs further reduce cancer cells’ ability to use estrogen to grow. Healthcare providers may recommend these drugs if other hormone therapies are ineffective or when a patient has an advanced form of hormone receptor-positive cancer.

Effectiveness and Side Effects

Overall research shows hormone therapy breast cancer patients live longer and reduces the risk of recurrence, especially in those with early-stage hormone-sensitive breast cancers. It can be a standalone treatment or combined with other therapies to improve outcomes.

However, although hormone therapy is a form of precision oncology, it is also a conventional treatment with side effects. Common ones include fatigue, mood swings, and hot flashes. In rare cases, aromatase inhibitors may lead to bone density loss, and SERMs like Tamoxifen may increase the risk of blood clots. Choosing a reliable and experienced healthcare team ensures careful monitoring and helps minimize adverse reactions to these medications.

 

2. HER2-Targeted Therapy

HER2-targeted therapy is a groundbreaking advancement in breast cancer care, particularly for HER2-positive breast cancers. What discerns this aggressive disease from other breast cancers is an overexpression of the HER2 protein, a growth-promoting agent on the surface of cancer cells. Only 15 to 20% of breast cancers are HER2-positive, but they grow and spread faster than others. HER2-targeted therapies target this protein to disrupt further cancer development.

 

Types of HER2-Targeted Therapy

Several HER2-targeted therapies are available, each with unique mechanisms for fighting cancer cells:

  • HER2-Specific Monoclonal Antibodies: These therapies use lab-made antibodies that attach to HER2 receptors, blocking the receptors and activating the immune system to attack the cancer cells. Some examples of monoclonal antibodies include:
    • Trastuzumab (Herceptin): One of the first and most widespread HER2-targeted therapies, Trastuzumab binds to HER2 receptors on cancer cells, slowing tumor growth and marking cells for immune destruction. In many cases, doctors use trastuzumab alongside chemotherapy for improved effectiveness.
    • Pertuzumab (Perjeta): Often prescribed with Trastuzumab, Pertuzumab binds to a different area on the HER2 receptor to perform a dual blockade. This combination therapy is most effective for advanced or metastatic HER2-positive breast cancer.
  • HER2-Specific Antibody-Drug Conjugates: ADCs are a newer approach that integrates antibodies with powerful cancer-killing drugs. They deliver chemotherapy to HER2-positive and triple-negative cancer cells while limiting the impact on healthy cells, unlike with traditional chemo that affects both malignant and normal cells in the body.
    • Ado-trastuzumab emtansine (Kadcyla): Kadcyla links Trastuzumab with a chemotherapy drug to create a “smart bomb.” After attaching to the HER2 receptor, it releases the chemotherapy drug into the cancer cell, boosting treatment efficacy while keeping the side effects of chemo to a minimum.
    • Fam-trastuzumab deruxtecan-nxki (Enhertu): About 87% of patients treated with this drug achieved disease control. It improves outcomes for both HER2-positive and HER2-low breast cancers.
  • HER2-Specific Tyrosine Kinase Inhibitors: These oral medications curb the activity of HER2 from inside the cancer cell by inhibiting enzymes (kinases) vital for cell growth. Leading examples of TKIs include Lapatinib (Tykerb) and Neratinib (Nerlynx).

 

Effectiveness and Side Effects

HER2-targeted therapies have improved the outlook for HER2-positive breast cancer patients, helping to manage the disease and extend life expectancy.

However, like all treatments, HER2-targeted therapies can come with side effects. The most common are digestive issues (like nausea and diarrhea), fatigue, and skin reactions. Monoclonal antibodies, particularly Trastuzumab and Pertuzumab, may raise the risk of high blood pressure and other cardiologic conditions. Regular heart monitoring is imperative throughout treatment to ward off such issues.

 

3. Antibody-Drug Conjugates

As mentioned, ADCs combine two components: an antibody that recognizes and binds to specific proteins on cancer cells, and a chemotherapy drug, or “payload,” that kills the cells. This treatment delivers chemotherapy directly to cancer cells, minimizing exposure to healthy cells and reducing side effects.

 

Types of Antibody-Drug Conjugates

Aside from HER2-positive Kadcyla and Enhertu, one other example of ADC is:

  • Sacituzumab govitecan-hziy (Trodelvy): This drug targets a protein called Trop-2, which is common on triple-negative breast cancer cells. It’s most beneficial for patients with advanced TNBC who have undergone prior treatments without success, as it provides a new option for this aggressive and difficult-to-treat disease.

 

4. CDK4/6 Inhibitors

CDK4/6 inhibitors are a class of targeted therapy drugs used primarily for hormone receptor-positive, HER2-negative breast cancers. These drugs work by blocking specific proteins involved in cell division, helping to suppress cancer cells from growing and spreading. CDK4/6 inhibitors are a breakthrough advancement, particularly for patients with advanced or metastatic breast cancer, as they can delay disease progression and improve survival rates.

 

Types of of CDK4/6 Inhibitors

Several CDK4/6 inhibitors have been developed and approved for breast cancer treatment:

  • Palbociclib (Ibrance): The first CDK4/6 inhibitor approved for hormone receptor-positive, most clinicians combine Palbociclib with aromatase inhibitors like Letrozol or SERDs like Fulvestrant. Studies show that these integrations prolong progression-free survival than hormone therapy alone.
  • Ribociclib (Kisqali): This targeted cancer drug works similarly to Palbociclib. It improves survival rates and delays progression when administered with endocrine therapy instead of combination chemotherapy.
  • Abemaciclib (Verzenio): Patients must take this drug continually for two years, or until cancer returns or unacceptable toxicity arises. Abemaciclib is effective as a combination therapy with hormone treatments or as a monotherapy in cases where other treatments do not work. Ongoing research also found that abemaciclib may cross the blood-brain barrier, suggesting it may treat secondary brain cancer.

 

Effectiveness and Side Effects

CDK4/6 inhibitors, often in combination with hormone therapy, give breast cancer patients more time and improve their quality of life. Any side effects that occur are often manageable and may include fatigue, low white blood cell count (neutropenia), and digestive issues. In rare instances, blood clots or lung inflammation may occur. Physicians keep a watchful eye on these unwanted effects to maintain a balance between treatment effectiveness and patient well-being.

 

5. PARP Inhibitors

PARP inhibitors are a class of targeted therapy drugs that obstruct the activity of PARP enzymes, which play a role in DNA repair within cells. These drugs address breast cancers associated with BRCA1 and BRCA2 mutations, as such cancers rely on the PARP pathway to repair damage to their DNA. By hampering this pathway, PARP inhibitors prevent cancer cells from repairing themselves, ultimately leading to their death.

 

Types of PARP Inhibitors

These medications exploit the genetic vulnerabilities of BRCA-related cancers and limit their ability to repair DNA:

 

Effectiveness and Side Effects

Originally approved for ovarian cancer, Olaparib has expanded to treat advanced or metastatic HER2-negative breast cancer with BRCA mutations, making it an effective treatment option for patients whose cancers have progressed after standard chemotherapy.

PARP inhibitors also come with potential side effects. Common ones include nausea, tiredness, anemia, diarrhea or constipation, and loss of appetite. In rare cases, PARP inhibitors may cause liver toxicity or a blood disorder called myelodysplastic syndrome. Healthcare providers closely monitor for these side effects and adjust treatment doses as needed.

 

6. PI3K/AKT/mTOR Inhibitors

PI3K/AKT/mTOR inhibitors are a group of targeted therapies used to treat certain breast cancers by interfering with the PI3K/AKT/mTOR signaling pathway, which is necessary for cell growth, regeneration, and division. In many cancers, this pathway becomes overactive, fueling uncontrolled cell growth. Inhibiting its different points can decelerate or stop cancer cells from invading the entire breast and spreading to other organs.

 

Types of PI3K/AKT/mTOR Inhibitors

The following medications may help patients whose breast cancer cells rely on this channel for survival:

  • PI3K Inhibitors: These drugs focus on the PI3K protein within the pathway, thwarting the first step in the signaling cascade.
    • Alpelisib (Piqray): Approved for use in advanced hormone receptor-positive, HER2-negative breast cancer with PIK3CA mutations, Alpelisib blocks the PI3K enzyme to inhibit cancer cell growth. It’s often used in combination with hormone therapies to maximize progression-free survival. Clinical studies indicate that life expectancy at 6 and 12 months were 91.9% and 75.2%, respectively.
  • mTOR Inhibitors: These medications target the mTOR protein, which plays a role in the PI3K-AKT-mTOR axis’s cell development and protein production stages.
    • Everolimus (Afinitor): Integrated with aromatase inhibitors like Exemestane, this drug delays progression, especially in cases when cancer stopped responding to endocrine therapy alone.

 

Effectiveness and Side Effects

When combined with hormone therapy, these inhibitors can be more effective at suppressing tumor development. However, like the rest of the medications in this article, PI3K/AKT/mTOR inhibitors may cause some side effects, which vary depending on the specific inhibitor. These side effects may include fatigue, high blood sugar levels (hyperglycemia), high levels of fats like cholesterol or triglycerides in the blood (hyperlipidemia), and mouth ulcers (stomatitis).

 

How Do Doctors Administer Targeted Therapies?

Oncologists deliver these treatments in one of two forms:

  • Oral medications: Patients can usually take these prescription drugs at home.
  • Injections: These treatments require scheduled visits to a hospital or clinic, where healthcare professionals administer each dose to ensure precision and monitor any immediate effects.

 

Treatment Frequency

The schedule for taking targeted therapy drugs depends on the patient’s specific medication and treatment plan:

  • Daily, weekly, or monthly: Some drugs require a regular schedule, such as daily, weekly, or monthly doses.
  • Cyclic treatments: Certain therapies follow cycles with active treatment periods followed by breaks. This approach helps manage the body’s response and minimize side effects.

Frequency and duration also depend on factors like the type of cancer, stage, and how the body responds to treatment.

 

Monitoring and Adjustments

Treatment experiences vary widely. It’s challenging to predict how each person will feel during targeted therapy, as responses differ from one patient to another. To monitor progress, manage any side effects, and adjust doses if necessary, oncologists schedule regular follow-up visits.

 

Another Treatment Option: Immunotherapy for Breast Cancer

Immunotherapy is one of the most innovative and advanced approaches to cancer treatment. It harnesses the body’s own immune system to reveal and attack cancer cells.

Some immunotherapies are considered “targeted” in the sense that they zero in on immune checkpoints or specific immune system proteins (e.g., PD-1/PD-L1) to allow a more focused immune attack on cancer cells. Immunotherapy is also part of precision oncology, as it tailors treatment to the unique characteristics of each person’s cancer and immune response.

Learn everything about how immunotherapy works for breast cancer here.

 

Recap: Overview of Targeted Therapies for Breast Cancer Subtypes

To reiterate, different breast cancers respond to specific targeted therapies. Here’s an overview of the most effective treatment options for each subtype:

For HR-positive breast cancer:

  • CDK4/6 inhibitors
  • Antibody-drug conjugates
  • mTOR inhibitors
  • PI3K inhibitors
  • Immunotherapy

 

For HER2-positive breast cancer:

  • Monoclonal antibodies
  • Kinase inhibitors
  • Antibody-drug conjugates
  • Immunotherapy

 

For triple-negative breast cancer:

  • Antibody-drug conjugates
  • PARP inhibitors
  • Immunotherapy

In certain cases, combining these therapies can optimize treatment effectiveness and improve patient outcomes. If you have questions or would like to book a consultation, please contact us at 480-666-1403.

 

About New Hope Unlimited

At New Hope Medical Center, we follow a comprehensive, compassionate approach to cancer care, addressing not just the physical symptoms but also the emotional and spiritual needs of each patient. Our dedicated team combines advanced targeted therapies with holistic care to support the entire person on their path to remission. If you or someone you know is seeking a personalized treatment program in a warm, patient-centered environment, reach out to us today.

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