Effect of radiotherapy on the interpretation of routine follow-up mammography after conservative breast surgery: a randomized study.

Radiotherapy after conservative surgery causes fat necrosis, fibrosis, skin thickening and other parenchymal distortion of the breast. The interpretation of a mammogram of the irradiated breast may therefore be difficult. We studied the effect of radiotherapy on the interpretation of the routine mammography used in the follow-up of breast cancer patients. A total of 144 low-risk breast cancer patients were randomized to radiotherapy or to no further treatment after conservative surgery. The first routine follow-up mammography was performed 18 months after surgery and every 18 months after that. The number of mammography examinations was estimated per patient and per follow-up year. The number of extra diagnostic tests and the occurrence of positive findings were assessed per mammography session and per follow-up year. Further diagnostic tests prompted by difficulties in interpreting the mammogram were performed to an extent of 0.19 per mammography examination in the radiotherapy group and of 0.15 in the non-radiotherapy group, i.e. 1.3 times more often. Findings that turned out to be negative at confirmation were 2.0 times (P< 0.05) more common in the radiotherapy group. These false-positive findings were more common in the radiotherapy group than in the surgery group and only shortly after treatment. Mammography is more difficult to interpret after radiotherapy than after conservative surgery alone, especially shortly after treatment, and more often involves extra diagnostic tests and findings that will be negative at confirmation.