Trastuzumab is a medication often discussed in cancer treatment, leading to questions about its classification. Patients and caregivers commonly wonder if it falls under immunotherapy or targeted therapy. This article clarifies Trastuzumab’s distinct mechanisms and explains why it is primarily considered a targeted therapy, despite some indirect immune-related effects.
Understanding Trastuzumab
Trastuzumab, widely known by its brand name Herceptin, is a type of medication called a monoclonal antibody. It is specifically designed to treat cancers that produce an excess of a protein called human epidermal growth factor receptor 2, or HER2. These cancers are referred to as HER2-positive, a characteristic found in approximately 20-30% of breast cancers and also in some stomach and gastroesophageal junction cancers.
The HER2 protein acts like a growth signal receiver on the surface of cancer cells, promoting their rapid growth when overexpressed. Trastuzumab works by binding directly to the extracellular portion of these HER2 receptors. This binding action blocks the signals that drive cancer cell growth and survival, effectively slowing or stopping the cells.
Trastuzumab’s primary mechanism involves directly interfering with specific molecular pathways within the cancer cell. It disrupts the signaling cascades normally activated by HER2, which contribute to tumor growth. By inhibiting these pathways, Trastuzumab helps to control the cancer.
Understanding Immunotherapy
Immunotherapy represents a different approach to cancer treatment, focusing on harnessing the body’s own immune system to combat the disease. Instead of directly attacking cancer cells, these treatments activate or enhance the patient’s immune response. The goal is to enable the immune system to recognize, target, and destroy cancerous cells more effectively.
Various forms of immunotherapy exist, each working through distinct mechanisms to boost immune function. For example, immune checkpoint inhibitors block proteins that normally act as “brakes” on the immune system, allowing immune cells to mount a stronger attack against cancer. Other types include adoptive cell therapies, such as CAR T-cell therapy, where a patient’s own immune cells are genetically modified in a laboratory to better recognize and eliminate cancer cells before being reinfused.
Cancer vaccines are another form of immunotherapy, designed to train the immune system to identify and attack cancer-specific proteins. The common thread among these diverse strategies is their focus on stimulating or restoring the immune system’s natural ability to fight cancer.
How Trastuzumab Differs from Immunotherapy
While Trastuzumab is a monoclonal antibody, its primary mechanism of action classifies it as a targeted therapy rather than an immunotherapy. Targeted therapies directly interfere with specific molecules or pathways that drive cancer growth and survival within cancer cells. Trastuzumab exemplifies this by binding directly to the HER2 protein on cancer cells, blocking growth signals from these receptors.
This direct blocking of HER2 signaling is Trastuzumab’s main function. Immunotherapy, by contrast, primarily works by unleashing or boosting the patient’s own immune cells, such as T-cells, to recognize and destroy cancer cells. Immunotherapies activate the immune system as a whole, often by removing its natural “brakes” or by training immune cells to be more effective cancer fighters.
It is true that Trastuzumab can elicit a secondary, indirect immune-mediated effect known as antibody-dependent cell-mediated cytotoxicity (ADCC). In ADCC, Trastuzumab, once bound to HER2-positive cancer cells, acts as a flag, signaling the body’s natural killer (NK) cells to attack and destroy the marked cancer cells. However, this immune recruitment is a consequence of its direct binding to a cancer-specific target, not a primary mechanism of broad immune system activation or modulation like that seen with checkpoint inhibitors or CAR T-cell therapy.
Therefore, while Trastuzumab leverages an antibody and can indirectly involve immune cells, its classification as a targeted therapy stems from its direct action on a specific molecular target (HER2) on cancer cells. Immunotherapy focuses on enhancing or restoring the immune system’s general ability to detect and eliminate cancer.