Paget disease of the breast with invasion from nipple skin into the dermis: an unusual type of skin invasion not associated with an adverse outcome.

Context: Paget disease is an uncommon skin manifestation of breast cancer, associated with either invasive carcinoma or ductal carcinoma in situ in the underlying breast. In very rare cases, tumor cells within the epidermis invade through the basement membrane of the skin into the dermis.
Objectives: To identify a series of cases of Paget disease with direct dermal invasion and to investigate the clinicopathologic features and outcome.
Design: Cases were identified during a 6-year period from the files of 2 hospitals. The clinical histories, imaging studies, and pathology reports were reviewed.
Results: Seven patients were identified, 5 with microinvasion (<0.1 cm) and 2 with 0.2- or 0.3-cm invasive carcinomas in the dermis. No lymphovascular invasion was seen. Sentinel nodes were negative in 3 patients who underwent biopsy. Five patients were treated with breast conservation with radiation. Three patients were at high risk for breast cancer because of prior breast cancer, Li-Fraumeni syndrome, or radiation for Hodgkin disease. The latter 2 patients underwent bilateral mastectomies. Three patients received hormonal therapy and 1 oophorectomy. No patient received chemotherapy. At follow-ups ranging from 4 to 66 months (median, 20 months), there have been no recurrences.
Conclusions: Patients with direct dermal invasion from Paget disease had a favorable outcome during the available follow-up period. This type of dermal involvement must be distinguished from locally advanced invasive carcinomas with skin invasion classified as T4b in the American Joint Cancer Commission staging system, as cancers with other types of skin invasion are associated with a poor prognosis.