How does trastuzumab exert its effect on breast cancer cells?

Trastuzumab is a monoclonal antibody that specifically targets the HER2 receptor, which is overexpressed in some breast cancer cells. By binding to the extracellular domain of the HER2 protein, trastuzumab disrupts the signaling pathways that promote tumor growth and proliferation. This interference can inhibit the cellular processes that lead to cancer progression and promote apoptosis (programmed cell death) in these HER2-positive breast cancer cells.

The mechanism of action of trastuzumab is pivotal in treating breast cancers characterized by HER2 overexpression, as these tumors are often more aggressive and less responsive to conventional therapies. In addition to directly inhibiting HER2 signaling, trastuzumab is thought to enhance the immune system's ability to target the cancer cells and may also have effects on tumor angiogenesis indirectly by disrupting the tumor's signaling environment.

The other options do not reflect the mechanism by which trastuzumab operates in the context of breast cancer. Increasing tumor angiogenesis pertains to promoting blood vessel formation, which does not align with the anti-cancer role of trastuzumab. Inhibiting T-cell activation and blocking estrogen receptors are mechanisms associated with other therapies and do not describe trastuzumab's specific action on HER2-positive breast cancer cells.