What is the primary action of Erlotinib in cancer treatment?

Erlotinib primarily acts by inhibiting the epidermal growth factor receptor (EGFR) tyrosine kinase, which is a crucial component in the signaling pathways that promote tumor growth and survival in certain types of cancers, particularly non-small cell lung cancer (NSCLC) and pancreatic cancer. By blocking the phosphorylation of tyrosine residues on EGFR, Erlotinib disrupts downstream signaling pathways that lead to cancer cell proliferation and anti-apoptotic responses, ultimately inhibiting tumor growth.

This mechanism is particularly effective in tumors that express EGFR, as it helps to halt the processes that contribute to tumor development and resistance to conventional therapies. Unlike the other options listed, which involve different mechanisms such as vascular endothelial growth factor inhibition or immune modulation, Erlotinib specifically targets the tyrosine kinase activity of EGFR, making it a critical therapeutic agent in managing certain malignancies that depend on this pathway for their growth and survival.