Why is the success rate of chemotherapy very low? And is it possible to improve that?

A thorough review, congratulations. I am particularly interested in patient's motives for adjuvant chemotherapy. From the fact that the minimum absolute increase in survival that participants considered sufficient to make an adjuvant chemotherapy (aCT) worthwhile ranged from 0.1% to 7%, i.e. a factor 70, one might conclude that a good many participants took this decision purely driven by emotions. A sizable portion even seemed to accept (have accepted) for little or no benefit. This I find very disturbing, much more disturbing than what you called disturbing, i.e. that expectancy of better survival was a driving factor in patients who preferred MAST over BCS. MAST and BCS have the same (very low) operative low mortality and morbidity (excluding psychic effects of grade of mutilation). This cannot be said of aCT compared to no-aCT. Most patients have been familiarized more or less with loss of hair and other conspicuous complications of aCT, but do not know that people die from aCT and many of them months or even years earlier than they would have without it. They do not know how aCT might drive you sick to death, how deeply tired people may feel after this treatment and so forth. Many chemotherapists sell aCT still as a kind of security: “You probably have been cured anyway by your surgery but in case there still are some cancer cells left, this cure [a misleading term] will take care of them”. Sounds irresistible, doesn’t it? When doctors are prepared to give their patients more insight they frequently do not use absolute but relative percentage numbers that of course are much higher and thus misleading as well. So, in my mind all your recommendations listed under the heading “Clinical implications” should be taken to heart by all doctors who treat patients with cancer.