Perhaps some oncologists are of the opinion that if the AC is done first, followed by the 12 Paclitaxol, that some patients may feel burnt out by around 8 - 10 of the Taxol and decline to finish the course...even if no major side effects, but "Just sooo over it"" type reaction. They may feel that if the (majority opinion) easier taxol is finished, then the relatively smaller number of 4 AC might have a greater completion rate. If the patient starts flagging, it may be easier to nudge them across the line with only 4 treatments. At the end of the day, its main course, then pudding. The same kilojoules are consumed if the chocolate mousse is eaten before the roast beef.