All Tumours Are Different
Breast cancer can be divided into 11 different types, each of which can be divided into subcategories. None two patients have the exact same tumours, and so, they will react differently to therapy.
The tremendous variation is firstly due to the fact that cancer can originate in different cell types – in the breast it might be mammary gland cells or connective tissue cells. Secondly, cancer cells mutate quickly, so they all develop differently.
The differences between the tumours mean that a treatment that is extremely efficient in one cancer patient has no effect in another patient.