You may not be sure of "failed", but I am, and apparently many cancer specialists agree with me as quoted in this article that addresses the issued more clearly than I could:

http://www.alive.com/articles/view/...of_chemotherapy

Here is a quote from the article:

"Another disturbing fact about chemotherapy is that the majority of specialists who prescribe such drugs would refuse to take them if they or their families had cancer themselves. According to one survey published in the Journal of Clinical Oncology in 1987, 81 percent of cancer specialists would not consent to a drug trial due to the ineffectiveness of chemotherapy and its unacceptable degree of toxicity."

Pointing to cases were cancer has been "cured" or sent into remission by chemotherapy offers little support for its effectiveness. What would have happened if no treatment other than change in diet and lifestyle had been undertaken or if some alternative had been undertaken? Maybe people who are treated with chemotherapy survive in spite of the treatment instead of because of it. Just because the medical/drug monopoly has endorsed the slash, burn, poison approach means nothing other than once government and special interests collude to exclude competition then people are limited to what serves those controlling the market. When "knowledge" gets institutionalized and is profitable to special interests, it stagnates.