Chemotherapy drug dose alteration due to radiation therapy in an adjuvant situation in breast cancer.

Fifty-six patients with T1-T3 and T2-T3 N0 medial lesions of breast carcinoma were randomized after modified radical mastectomy to receive either cytoxan, methotrexate, 5-fluorouracil (5-Fu) (CMF) chemotherapy for 1 year (group A) or CMF for 1 year and postoperative radiation therapy (group B). Thirty-two patients received chemotherapy alone and 25 patients received both chemotherapy and radiation therapy. Twenty-five of 32 group A patients (median age 52) and 20/24 group B patients (median age 50) were evaluable. Leukopenia was the major cause of drug dose reduction in both groups. In group A, 4/25 patients (16%) had leukopenia at less than the 2500 level, whereas 8/20 (40%) group B patients had leukopenia at the same level. If 70% of all three drug dosages are considered as adequate chemotherapy, 21/25 (84%) patients received adequate chemotherapy in group A, and 10/20 (50%) in group B (p approximately equal to 0.029 from contingency table). It appears that radiation therapy in postmastectomy patients hinders adequate drug dose delivery in an adjuvant setting.