Pathway complexity

The rationale for developing Herceptin was straightforward: by inactivating the HER2 cell surface receptors overexpressed in certain breast cancer cells, the cascade leading to tumorigenesis can be halted. But it turned out not all patients who overexpress HER2 respond, for reasons that are not fully understood. One possibility is related to the loss of the tumor suppressor PTEN.

(1) Normally, Herceptin binds HER2, an epidermal growth factor (EGF) receptor - thus downregulating the PI3K-Akt-mTOR cascade leading to tumor growth...