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

None: If there is metastatic disease ( spreading ) to distant organ - we call it as a stage iv. We don't classify it further to 4a, b or c.- in breast cancer. In head and neck cancer, on the other hand, we do divide stage IV in to iva, ivb and IV c.

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.