I am not sure about what the sister drug of Erbitux is, but my Dad was diagnosed in February with Stage IV colon cancer and as soon as chemo began, Erbitux was part of his treatment. He has developed a rash, which looks more like acne than anything, but other than that he has managed fine with it! We are awaiting the results of his first CT scan and I suppose until then we will not know how the Erbitux is actually doing, or any drug for that matter, but on the outside he looks wonderful and his appetite, energy, and life have returned.