A

Abscess: a collection of pus within the breast. This is most commonly associated with lactation (breast-feeding) and is sometimes related to ascending infection from the duct orifices on the nipple. It may be associated with periductal mastitis (see entry). After confirmation of the diagnosis by clinical examination and ultrasound scan, treatment is with antibiotics and / or needle aspiration of the pus in the first instance. The bacterial sensitivity of the pus culture can help guide further antibiotic treatment. Conservative treatment of breast abscesses without surgery is usually successful. Sometimes, formal surgical drainage may be necessary in an established chronic abscess.

Adjuvant treatment: additional treatment in addition to surgery, which forms the multidisciplinary management of breast cancer. Adjuvant treatment can include chemotherapy (see entry), radiotherapy (see entry) and endocrine therapy (see entry).

Atypia: the presence of abnormal appearing cells assessed by fine needle aspiration for cytology or tissue sample for histology.

Atypical ductal/lobular hyperplasia: microscopic appearances of cells that are risk factors for cancer, but in themselves are not cancer.

Axillary dissection: a more extensive operation compared to axillary sampling (see entry), to remove nodes according to defined anatomical boundaries in the armpit. Level I is the lowest dissection while level III is a complete axillary clearance. Anatomically, a level I dissection involves removal of the axillary nodes lateral to the outer border of the pectoralis minor muscle. Level II is an extension of a level I dissection to the inner border of the pectoralis minor muscle, and a level III dissection extends beyond level II to the apex of the axillary space, adjacent to the first rib behind the collar bone. In general, there are 5 to 15 nodes in level I, 3 to 7 nodes in level II, and 1 to 5 nodes in level III. As breast cancers are picked up at an earlier stage, a level I dissection may be suitable for smaller screen detected cancers. A level II dissection is often called a "clearance", but a true axillary clearance is a level III operation. Some surgeons would only remove level III nodes if level II nodes are clinically involved. An axillary clearance operation is therapeutic in the presence of positive nodes.

Axillary sampling: an operation to remove a sample of nodes from the low axilla, usually at least four, for evaluation of prognosis and to determine adjuvant treatment. There is sometimes an overlap between what some surgeons call an axillary sampling and the lowest level of axillary dissection (see entry). See also lymph node status entry.