Targeted Therapies
What are Targeted Therapies?
Targeted therapies are medicines that find and attack specific parts of breast cancer cells. They interfere with proteins that cause the cancer cells to grow and spread. As experts find more markers in the cancer cell to target, more therapies are developed for people with breast cancer.
HER2- Targeted Therapies
Some breast cancers have high levels of a protein called human epidermal growth factor receptor 2 (HER2). When cancer cells make too much HER2, they grow and divide more quickly. HER2-targeted therapies are designed to attach directly to this protein and stop those growth signals.
Because these medicines are directed at a specific marker, they can reduce some side effects compared with general chemotherapy. Newer HER2-targeted therapies are useful even in patients with low levels of HER2 expression.
Types of HER2-Targeted Medicines
HER2 therapies come in several forms and may be given by IV infusion, injection under the skin, or pill.
Cyclin-Dependent Kinase (CDK) 4/6 Inhibitors
CDK4/6 inhibitors are typically used alongside endocrine therapy. They help slow the growth of cancer cells.
In healthy tissue, cells divide in a carefully regulated way. Proteins called CDK4 and CDK6 act like switches that signal when a cell should grow and divide. In certain breast cancers, these switches are overly active, causing cells to multiply too quickly. CDK4/6 inhibitors block these proteins—essentially placing a “lock” on the switch—so cancer cells grow more slowly.
Available CDK4/6 Inhibitors
Three FDA-approved CDK4/6 inhibitors are currently used in clinical practice:
- Palbociclib (Ibrance®)
- Ribociclib (Kisqali®)
- Abemaciclib (Verzenio®)
Who may benefit from CDK4/6 inhibitors?
CDK4/6 inhibitors are approved for:
- Stage II-III breast cancer
- Metastatic (stage IV) HR+ breast cancer
For early-stage breast cancer with high risk of recurrence, adding 2 years of abemaciclib, or 3 years of ribociclib to endocrine therapy can reduce the risk of cancer returning.
For metastatic breast cancer, combining a CDK4/6 inhibitor with endocrine therapy can significantly extend the time before the cancer progresses and improve long-term survival.
Possible Side Effects from CDK4/6
These treatments can cause:
- Low blood counts
- Fatigue
- Nausea and/or vomiting
- Mouth sores
- Hair loss
- Diarrhea
Supportive strategies are available. Explore the Symptom Management pages for practical guidance.
PARP Inhibitors
PARP (poly ADP-ribose polymerase) is an enzyme that helps repair damaged DNA. PARP inhibitors are targeted medicines designed to block this repair process in cancer cells. When cancer cells are unable to repair DNA damage, they are more likely to die. The following treatments are used in specific breast cancers based on tumor type and genetic testing results.
Learn more about recognizing and managing side effects in the Symptom Management section.
Other Targeted Therapies for Metastatic Breast Cancer
PIK3CA, PTEN, and AKT1 Inhibitors
Some metastatic breast cancers are driven by changes (mutations) in genes that regulate how cells grow and survive. The PIK3CA gene is mutated in up to 35% of certain breast cancers, and mutations in PTEN and AKT1 can also occur, though less often.
When these genes are altered, they can activate a signaling pathway that fuels cancer growth. Targeted medicines — known as PIK3CA or AKT inhibitors — work by blocking this pathway. When combined with endocrine therapy, they may help treatment remain effective for a longer period of time.
Medications
Who May Benefit
Possible Side Effects
Selective Estrogen Receptor Downregulators (SERDs)
SERDs block and break down estrogen receptors. Although commonly classified as an endocrine therapy, they can also be particularly beneficial in those with an ESR1 mutation.
