Risk of pneumonitis in breast cancer patients treated with radiation therapy and combination chemotherapy with paclitaxel

Background: Some chemotherapy (CT) drugs, including, taxanes, may enhance t he effectiveness of radiation therapy (RT)., However, combining these thera pies may increase the incidence of radiation pneumonitis, a lung inflammati on. In a retrospective cohort study, we evaluated the incidence of radiatio n pneumonitis in breast cancer patients treated with RT and standard adjuva nt CT by use of doxorubicin (Adriamycin) and cyclophosphamide, with and wit hout paclitaxel., Methods: Forty-one patients with breast cancer were treat ed with RT and adjuvant CT, including paclitaxel. Paclitaxel and RT (to bre ast-chest wall in all and lymph nodes in some) were delivered sequentially in 20 patients, and concurrently in 21 patients. Paclitaxel was given weekl y in some patients and every 3 weeks in other patients. The incidence of ra diation, pneumonitis, was compared with that among patients in our database whose treatments did not include paclitaxel (n = 1286). The percentage of the lung volume irradiated was, estimated. The Cox proportional. hazards mo del was used to find covariates, that may be associated with the observed o utcomes. All P values were two-sided. Results: Radiation pneumonitis, devel oped in six of the 41 patients,. Three patients received paclitaxel concurr ently with RT., and three received it sequentially (P = .95). The mean perc entage of lung volume irradiated was 20% in patients who developed radiatio n pneumonitis and 22% in those who did not (P = .6). For patients treated w ith CT including paclitaxel, the crude rate of developing radiation pneumon itis, was 14.6% (95% confidence interval [CI] = 5.6% to 29.2%). For patient s treated with CT without paclitaxel, the crude rate of pneumonitis was, 1. 1% (95% CI = 0.2% to 2.3%)., The difference between the crude rates with or without paclitaxel is highly statistically significant (P < .0001). The me an time to develop radiation pneumonitis in patients treated concurrently w ith RT and paclitaxel was statistically significantly shorter in patients r eceiving paclitaxel weekly than in those receiving it every 3 weeks (P = .0 02). Conclusions: The use of paclitaxel and RT in the primary treatment of breast cancer should be undertaken with caution. Clinical trials with the u se of combination CT, including paclitaxel plus RT, whether concurrent or s equential, must evaluate carefully the incidence, of radiation pneumonitis.