Breast cancer stage IIa is considered early stage. Breast cancer is classified into stages 0, I, IIa, IIb, III, and IV. Stage III is further divided into IIIa, IIIb, and IIIc. Strictly speaking, breast cancers at stage IIa and earlier are considered early-stage breast cancer, while stage III is considered locally advanced breast cancer, including IIIa, IIIb, and IIIc, and stage IV is considered advanced breast cancer. However, since most operable breast cancers, which include up to stage IIIa (stages 0, I, II, and including IIIa), generally have favorable treatment outcomes, many research institutions and medical organizations in Western countries define all stages up to IIIa as early-stage breast cancer. Therefore, breast cancer stage IIa is classified as early-stage cancer.