Contralateral breast cancer after limited surgery plus radiotherapy of early mammary tumors.

Conservative treatment of early breast cancer with limited surgery requires a mandatory irradiation of the affected breast, which implies a low but measurable irradiation of contralateral breast too. As ionizing radiations can produce an oncogenic effect on mammary tissues, the series of 701 patients of the Milano clinical trial on T1 No breast cancer (1973-1980) was investigated to compare the incidence of contralateral breast cancer in the Halsted group (not irradiated) and in the QU.A.RT. group (irradiated on the operated breast with a total dose of 50 Gy plus a limited boost of 10 Gy). In March 1986, a contralateral breast cancer was diagnosed in 17/349 patients (4.9%) of the Halsted group and in 18/352 patients (5.1%) of the QU.A.RT. group after a median follow-up of 108 months. The sites of contralateral cancer were superimposable in the two groups of patients, with a constant prevalence of external quadrants, despite the great difference of dose distribution in the irradiated patients. Our data on the incidence of contralateral breast cancer failed to demonstrate an oncogenic effect of irradiation to date, but the follow-up is still in progress and any future event will be registered and discussed.