What is the difference between stage iva, ivb, and ivc breast cancer?

No difference: There is no further classification of stage IV in breast cancer. When the cancer spreads beyond the primary organ- i.e. Breast - to distant organs like lung, liver, bones, brain etc- we call this as stage iv.

T Stages: I think you are talking about primary tumor stage (eg t stage). T4a is a breast tumor that has grown into the chest wall, t4b is one that basically invokves the skin, t4c involves both chest wall and skin, and t4d is inflammatory carcinoma where the entire breast is red and swollen due to extensive cancer. These are combined with the nodal (n) and metastasis (m) stages to give overall stage.