Radiation-induced changes in the breast.

Thirty-six postirradiation breast tissue specimens from 30 patients with breast cancer treated by primary radiation therapy were evaluated to define the effects of therapeutic doses of ionizing radiation on the residual non-neoplastic breast tissue. Breast tissue was sampled an average of 30.4 months after completion of therapy because of the development of new clinically or mammographically detectable abnormalities within the treated breasts. The average radiation dose was 6,399 rad to the primary tumor area and 4,778 rad to the remainder of the breast. Breast tissue sections from 35 nonirradiated patients served as control specimens. The most characteristic radiation effects consisted of atypical epithelial cells in the terminal duct lobular unit ( TDLU ) associated with lobular sclerosis and atrophy. These changes were present in all of the irradiated patients but varied in severity and extent among patients and within individual patients. This variation was not related to the presence or absence of carcinoma elsewhere in the specimen, radiation dose, patient age, time to postirradiation tissue sampling, or use of adjuvant chemotherapy. Epithelial atypia in larger ducts, stromal changes, and vascular changes were less frequent but were always accompanied by prominent TDLU changes. Radiation effects could usually be clearly distinguished from carcinoma involving the TDLU by the absence of both cellular proliferation and distention of the involved TDLU and by the preservation of cellular polarity and cohesion in areas of presumed radiation-induced injury. Familiarity with these changes is of considerable practical importance in that they must be distinguished from new or recurrent neoplasms.