Contralateral breast cancer and other second malignancies in patients treated by breast-conserving therapy with radiation.

Metachronous contralateral breast cancers and other second malignancies were evaluated in 2,850 patients treated between 1960 and 1981 primarily with radiotherapy (RT) either alone or following breast-conserving surgery. One hundred eighty-four contralateral cancers were observed in 22,491 patient-years of observation (818 per 10(5) patient-years), with a cumulative probability of 4.5% at 5, 7.9% at 10, and 11% at 15 and 20 years. Compared to patients with unilateral tumors, those destined to develop contralateral cancers were younger (mean age 51.9 vs 56.6) and more often gave a family history of breast cancer. Contralateral breast cancers were more frequent for more extensive tumors (T3 10% vs T1-26%; with inflammatory signs 10.6% without 6%), and in patients with ipsilateral local recurrence (with 9.1%, without 5.6%). Patients with contralateral cancers had a significantly less favorable survival experience (15-year actuarial survival after primary therapy 42%) than patients without contralateral cancer (15-year survival 65.5%). In early stage patients treated with conservative surgery and RT, contralateral cancer was not prognostically more favorable than ipsilateral breast recurrence. Among 72 other second malignancies (320 per 10(5) patient-years) were 2 soft tissue sarcomas in the irradiated area. This corresponds to an incidence of 21 cases per 10(5) patient-years for survivors beyond the fifth year. The possible influence of RT on contralateral cancers and other second malignancies is discussed.