[en] Purpose: Chemotherapy plays an increasingly important role in the treatment of both node-negative and node-positive breast cancer patients, but the optimal sequencing of chemotherapy and radiation therapy is not well established. The purpose of this study is to evaluate the interaction of sequence and type of chemotherapy and hormonal therapy given with radiation therapy on the cosmetic outcome and the incidence of complications of Stage I and II breast cancer patients treated with breast-conserving therapy. Methods and Materials: The records of 1053 Stage I and II breast cancer patients treated with curative intent with breast-conserving surgery, axillary dissection, and radiation therapy between 1977-1991 were reviewed. Median follow-up after treatment was 6.7 years. Two hundred fourteen patients received chemotherapy alone, 141 patients received hormonal therapy alone, 86 patients received both, and 612 patients received no adjuvant therapy. Patients who received chemotherapy ± hormonal therapy were grouped according to sequence of chemotherapy: (a) concurrent = concurrent chemotherapy with radiation therapy followed by chemotherapy; (b) sequential = radiation followed by chemotherapy or chemotherapy followed by radiation; and (c) sandwich = chemotherapy followed by concurrent chemotherapy and radiation followed by chemotherapy. Compared to node negative patients, node-positive patients more commonly received chemotherapy (77 vs. 9%, p < 0.0001) and/or hormonal therapy (40 vs. 14%, p < 0.0001). Among patients who received chemotherapy, the majority (243 patients) received concurrent chemotherapy and radiation therapy with two cycles of cytoxan and 5-fluorouracil (5-FU) administered during radiation followed by six cycles of chemotherapy with cytoxan, 5-fluorouracil and either methotrexate(CMF) or doxorubicin(CAF). For analysis of cosmesis, patients included were relapse free with 3 years minimum follow-up. Results: The use of chemotherapy had an adverse effect on cosmetic outcome compared to no chemotherapy, which was of borderline significance at 3 years (92% excellent or good cosmetic outcome vs. 96% respectively, p = 0.057); however, cosmesis was not different at 5 years (91 vs. 93% respectively, p = 0.67). Cosmesis was not significantly different between patients treated sequentially and those treated concurrently (3 year: 87 vs. 93% respectively, p = 0.33), nor was it different between patients who received CMF vs. CAF (3 year: 92 vs. 93% respectively, p = 0.89). Hormonal therapy did not influence cosmetic outcome (p = 0.78). The incidence of Grade 4 or 5 arm edema (≥ 2 cm difference in arm circumference) was 2% without chemotherapy vs. 8% with chemotherapy (p 0.00002). However, the incidence of arm edema was not affected by sequencing or type of chemotherapy (all p ≥ 0.52). Patients treated sequentially had a 10% incidence of Grade 4 or 5 arm edema vs. 7% in the patients treated concurrently (p = 0.52). The incidence was 7 vs. 9% in patients treated with CMF vs. CAF (p = 0.73). The incidence of clinical pneumonitis and rib fracture was not influenced by use of chemotherapy, sequence of chemotherapy or use of hormonal therapy (all p ≥ 0.06). Conclusions: Chemotherapy can be given concurrently with radiation therapy in the treatment of Stage I and II breast cancer with breast-conserving therapy without seriously compromising cosmetic outcome or incidence of complications compared to patients receiving other sequences of chemotherapy. Hormonal therapy did not affect cosmesis or complications. The chemotherapeutic regimen of cytoxan and 5-FU concurrent with radiation therapy followed by more chemotherapy is one reasonable option for breast conservation therapy in patients requiring chemotherapy