Paget's disease of the breast is a form of cancer that primarily affects the skin of the nipple and sometimes the areola as well. It is a rare ailment that was first described in 1874 by Sir James Paget. Many cases of Paget's disease are associated with an underlying breast carcinoma.
Paget's disease of the breast (PDB) is a carcinoma of the breast that involves the nipple and the areola. It is a rare disease and is usually linked to carcinoma in situ, or an invasive carcinoma in the breast, which may be evidenced by a palpable mass on examination of the breast . PDB constitutes only about 1-4% of reported cases of breast cancer in females . About 40% of those associated with invasive cancer are associated with ductal carcinoma in situ . PDB can occur in both men and women, however, it predominantly affects the latter. The disease is often diagnosed in the 5th decade, although cases of younger and older-onset have been reported . PDB often presents as unilateral disease. It can occur in accessory nipples, as well as non-breast tissue after mastectomy  . Furthermore, it has been reported to occur in the breast tissue in the axilla .
PDB affects the skin and causes lesions that may resemble eczema . For this reason, it may be misdiagnosed as a dermatological condition. The nipple and areola are often erythematous, itchy, flaky, and sometimes there is an erosion of the nipple. A nipple discharge is not uncommon and may range from serosanguineous to purulent. Other reported findings are ulceration, bleeding, thick plaque formation, and pain that is often burning in nature.
Paget's disease of the breast has four stages, stage zero describing malignancy that only involves the epidermis, and stage four being PDB that is associated with invasive ductal carcinoma. There are several modalities that are used in the diagnosis of PDB. Clinical breast examination is of particular importance as up to 50% of those with PDB will have a palpable breast lump. Subsequent diagnostic techniques involve both invasive and noninvasive strategies.
Breast tissue from the affected area should be analyzed histologically, thus necessitating a biopsy. The choice of what type of biopsy to carry out ranges between wedge, punch, shave and surface biopsy. Immunochemistry is also carried out on biopsy samples. Together, the above laboratory techniques (immunohistochemistry) form the definitive diagnostic measure for PDB .
Imaging studies include mammography, ultrasound and magnetic resonance imaging (MRI) . These are useful in detecting nonpalpable breast masses . On mammography, PDB may cause distortion of the breast architecture, calcifications, edema, and nipple changes. Negative findings on mammography do not rule out the possibility of PDB, as about 70% of cases with histological evidence of the disease also have positive findings on mammography. Therefore there is a proportion of cases of PDB without mammographic features of the disease. MRI is useful in detecting PDB that otherwise goes undetected by the former .