The effect of postoperative and primary radiation therapy on delivered dose of adjuvant cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) chemotherapy in breast cancer.

The dose of adjuvant chemotherapy for breast cancer may be an important factor in the success of the treatment program. In a retrospective analysis, the authors determined whether patients who were irradiated either postoperatively (N = 29) or as part of primary treatment (N = 13) received a lower dose of adjuvant cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) chemotherapy than patients who were not irradiated (N = 42). The 84 evaluable patients received either cyclical or weekly CMF. Radiation therapy included the chest wall or breast and regional lymph nodes. The mean percentage of maximum chemotherapy dose delivered (59.9% versus 73.5%; P less than 0.001), mean percent prescribable or theoretical maximum dose (83.1% versus 91.3%; P less than 0.001), and mean leukocyte count (3.9 versus 4.5; P less than 0.01) during therapy were statistically significantly lower in irradiated patients. The lower delivered chemotherapy dose in irradiated patients was not related to the radiation dose to the thoracic spine. The authors conclude that radiation therapy to the chest wall or breast and regional lymph nodes reduces the dose of adjuvant CMF that can be delivered.