Stage III breast cancer is divided into subcategories known as IIIA, IIIB, and IIIC.
In stage IIIA, it’s possible there be no tumor. However, cancer may be found in axillary lymph nodes. In other cases, there is a tumor, of any size and it has also spread to axillary lymph nodes.
In stage IIIB, the cancer may be any size and has already spread to the wall of the chest and/or the breast skin and also may have spread to the axillary lymph nodes. It may also have spread to those lymph nodes near the breastbone.
For those experiencing inflamed, reddening, warmth and swelling of a large area of the breast, inflammatory breast cancer may be the reason. Inflammatory breast cancer is also considered to be at least stage IIIB and may mean that cancer cells have spread to lymph nodes and can be found in the skin.
https://www.empowher.com/brain-cancer/content/stage-three-breast-cancer