Why do we give four cycles of TC as adjuvant therapy when some of the clinical trials administered six cycles?

There are three trials I use to think about this issue: USOR 9735 (TC x 4 vs AC x 4, Jones et al JCO 2009; 27: 1177-1183), ECOG 1199 (AC x 4 with paclitaxel qw x 12, vs taxol q3w x 4, vs docetaxel qw x 12, vs docetaxel q3w x 4, Sparano et al JCO 2015; 33: 2353-2360) and the ABC analysis (TC x 6 vs T...