Immunotherapy represents a significant advancement in cancer treatment, harnessing the body’s own defense mechanisms. This approach differs from traditional therapies by empowering the immune system to recognize and eliminate cancerous cells. Breast cancer, a complex disease, benefits from various strategies, with immunotherapy emerging as a promising option for certain patients.
How Immunotherapy Works Against Breast Cancer
The immune system naturally identifies and eliminates abnormal cells through immune surveillance. Cancer cells, including those in the breast, can develop mechanisms to evade this.
One common strategy involves exploiting immune checkpoints, which are molecules on immune cells that regulate the immune response. Cancer cells often express proteins like programmed death-ligand 1 (PD-L1) on their surface. This protein can bind to a receptor called programmed death 1 (PD-1) found on immune T-cells, effectively sending a “don’t attack me” signal. This interaction normally helps prevent the immune system from attacking healthy tissues, but cancer cells hijack it to protect themselves from destruction. Another checkpoint involves the CTLA-4 protein, which also helps regulate T-cell activity.
Immunotherapy drugs, particularly checkpoint inhibitors, are designed to block these specific interactions. By preventing PD-L1 from binding to PD-1, or by blocking CTLA-4, these drugs “release the brakes” on the immune system. This action re-activates the T-cells, allowing them to recognize and mount an effective attack against the breast cancer cells. This mechanism is fundamentally different from chemotherapy, which directly kills rapidly dividing cells, or radiation, which uses high-energy beams to destroy cancer cells. This targeted approach leverages the specificity and memory of the immune system.
Current Immunotherapy Approaches for Breast Cancer
Current immunotherapy approaches for breast cancer primarily focus on immune checkpoint inhibitors. These medications are monoclonal antibodies, laboratory-produced proteins designed to target specific substances in the body. For breast cancer, the most established inhibitors target the PD-1/PD-L1 pathway.
Pembrolizumab is an example of a PD-1 inhibitor approved for certain types of breast cancer. It blocks the PD-1 receptor on T-cells, preventing cancer cells from deactivating the immune response. Atezolizumab targets the PD-L1 protein directly on cancer cells.
These checkpoint inhibitors are typically administered intravenously. The treatment schedule varies but often involves infusions every two to four weeks. The administration occurs in an outpatient setting, such as an infusion center or hospital.
While checkpoint inhibitors are the most prevalent, other immunotherapy approaches are under investigation for breast cancer. These include therapeutic vaccines, which aim to train the immune system to recognize specific cancer antigens, and oncolytic viruses, which are engineered viruses that infect and destroy cancer cells while stimulating an immune response. Checkpoint inhibitors remain the cornerstone of immunotherapy in breast cancer treatment. Their widespread use reflects their demonstrated efficacy in specific patient populations.
Who Benefits from Immunotherapy for Breast Cancer
Immunotherapy is not a universal treatment for all breast cancer patients, and specific criteria determine who is most likely to benefit. The effectiveness of immunotherapy is often linked to the presence of certain biomarkers within the tumor.
One biomarker is the expression of PD-L1 on tumor or immune cells within the tumor microenvironment. Patients with higher PD-L1 expression are more likely to respond to PD-1 or PD-L1 inhibitors. Pathologists assess PD-L1 levels through biopsy samples using specific scoring systems. Another factor is the presence of tumor-infiltrating lymphocytes (TILs), which are immune cells that have entered the tumor. Higher levels of TILs can indicate a more “inflamed” tumor that might be more susceptible to immune attack.
Immunotherapy has shown significant efficacy primarily in specific breast cancer subtypes. Triple-Negative Breast Cancer (TNBC) is a subtype that often lacks estrogen receptors, progesterone receptors, and HER2 protein, making it difficult to target with hormone therapy or HER2-targeted drugs. TNBC tumors frequently exhibit higher PD-L1 expression and more TILs, making them more amenable to immunotherapy. Immunotherapy is also being explored in combination with other treatments for HER2-positive breast cancer, especially in advanced stages.
The use of immunotherapy is also tied to the stage of the disease. It is approved for advanced or metastatic breast cancer in certain settings. Additionally, it is increasingly used in the neoadjuvant setting for high-risk early-stage breast cancer, particularly TNBC, to reduce tumor size and improve outcomes.
What to Expect During Immunotherapy Treatment
Immunotherapy for breast cancer is typically administered as an intravenous infusion. Patients receive the medication through a needle placed in a vein, often in the arm, over a period that can range from 30 minutes to several hours. The frequency of these infusions varies depending on the specific drug and treatment plan, commonly occurring every two, three, or four weeks.
Unlike chemotherapy, which often leads to side effects like hair loss and severe nausea, immunotherapy can cause immune-related adverse events (irAEs). These side effects occur because the activated immune system, now unleashed to fight cancer, can sometimes also attack healthy tissues and organs.
Common irAEs include fatigue, skin rashes, itching, and inflammation in various organs. More serious irAEs can involve the colon (colitis), lungs (pneumonitis), liver (hepatitis), or endocrine glands like the thyroid, leading to conditions such as hypothyroidism or hyperthyroidism. Patients may experience symptoms like diarrhea, shortness of breath, or changes in energy levels. These side effects require careful monitoring by the healthcare team.
Management of irAEs often involves corticosteroids, which are medications that suppress the immune system to reduce inflammation. The dose and duration of corticosteroids depend on the severity of the side effect. Responses to immunotherapy vary widely, but some patients experience durable and long-lasting disease control.