A C chemotherapy

Dizzy bird here again as you may know I was diagnosed on the fifth of august with bc grade 3 tumour size 5.5 cm
Still haven’t started treatment as yet due to having lymph nodes (not sure how many)removed Tuesday to see if the cancer has spread. Went today to get results but still not back yet. Was told they are changing my chemo from fec t 3 x 3 to ac 4 x 4, I’m a bit confused why it has been changed can anyone explain the differences between the two treatments and is one better than the other.I did ask but still don’t really understand as u all know we get told so much to much for me to take in be very grateful to any one who can help. the one thing they did say they was worried about my wound under my arm healing with fec t thanks db xx