To compare two different timings of radiation treatment in patients with breast cancer who underwent conservative surgery and were candidates to receive adjuvant cyclophosphamide, methotrexate, and fluorouracil (CMF) chemotherapy.

A total of 206 patients who had quadrantectomy and axillary dissection for breast cancer and were planned to receive adjuvant CMF chemotherapy were randomized to concurrent or sequential radiotherapy. Radiotherapy was delivered only to the whole breast through tangential fields to a dose of 50 Gy in 20 fractions over 4 weeks, followed by an electron boost of 10-15 Gy in 4-6 fractions to the tumor bed.

No differences in 5-year breast recurrence-free, metastasis-free, disease-free, and overall survival were observed in the two treatment groups. All patients completed the planned radiotherapy. No evidence of an increased risk of toxicity was observed between the two arms. No difference in radiotherapy and in the chemotherapy dose intensity was observed in the two groups.

In patients with negative surgical margins receiving adjuvant chemotherapy, radiotherapy can be delayed to up to 7 months. Concurrent administration of CMF chemotherapy and radiotherapy is safe and might be reserved for patients at high risk of local recurrence, such as those with positive surgical margins or larger tumor diameters.