In stage III breast cancer, the cancer cells have spread outside the breast tissue to the adiacent lymph nodes or to the thoracic muscles but they have not  moved to the distant organs. Even though in this stage the breast cancer is considered to be advanced, the 5 year survival rates in the USA and European Union countries range from 54 to 67 %.  There are several different forms of breast cancer stage III, depending on the size of the tumor the number of lymph nodes affected, or by the invasion into the chest wall or into the skin.

Almost all the forms of stage III breast cancer are operable, the only exception being the case in which the cancer cells have spread to the supraclavicular lymph nodes, this form representing the inoperable stage IIIC breast cancer. The stage III breast cancer is divided by most oncologist into other 3 stages. In stage IIIA there are many situations: no tumor can be found in the breast, but cancer has developed in the axillary lymph nodes (which may be either attached to each other or to the surrounding structures), or the cancer can affect the lymph nodes near the sternum.


Another situation in stage IIIA is when the tumor's diameter is up to 2 centimeters and cancer cells have spread to the axillary lymph nodes which may be as in the previously mentioned case attached to each other or to the surrounding tissues or the cancer has spread to the peristernal lymph nodes; or  another situation in which the tumor is has more than 2 to 5 cm in diameter and it  to the axillary  or other peristernal lymph nodes, or the case in which the tumor measures more than 5 centimeters and the cancer spreads to the axilary or peristernal lymphatic structures. The 5 year survival rate for this stage varies from 56% to 67% according to The American Cancer Society.


In stage IIIB, the tumor may have virtually any size and the cancer may have spread to the thoracic wall and/or the skin and it may have affected also axillary and peristernal lymph nodes and other close structures. The 5 year survival rate for stage IIIB breast cancer ranges between 49% and 54%.

In stage IIIC, the tumor may have any size or it may be even absent but it may have affected the chest wall and/or the skin.In this stage the cancer spreads to lymph nodes above and/or below the collarbone and to the lymph nodes in the axilar region and/ or near the breastbone. In operable stage IIIC, the cancer is usually found in 10 or more axillary lymph nodes, in the subclavicular lymph nodes or in the axillary and peristernal lymph nodes. In inoperable stage IIIC, the cancer has affected the supraclavicular lymph nodes (the lymph nodes above the collarbone). The Stage IIIC is considered to have a five-year survival rate of 36 to 50%.