Some chemotherapy (CT) drugs, including taxanes, may enhance the effectiveness of radiation therapy (RT). However, combining these therapies may increase the incidence of radiation pneumonitis, a lung inflammation. In a retrospective cohort study, we evaluated the incidence of radiation pneumonitis in breast cancer patients treated with RT and standard adjuvant CT by use of doxorubicin (Adriamycin) and cyclophosphamide, with and without paclitaxel.

Forty-one patients with breast cancer were treated with RT and adjuvant CT, including paclitaxel. Paclitaxel and RT (to breast-chest wall in all and lymph nodes in some) were delivered sequentially in 20 patients and concurrently in 21 patients. Paclitaxel was given weekly in some patients and every 3 weeks in other patients. The incidence of radiation 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 model was used to find covariates that may be associated with the observed outcomes. All P values were two-sided.

Radiation pneumonitis developed in six of the 41 patients. Three patients received paclitaxel concurrently with RT, and three received it sequentially (P =.95). The mean percentage of lung volume irradiated was 20% in patients who developed radiation pneumonitis and 22% in those who did not (P =.6). For patients treated with CT including paclitaxel, the crude rate of developing radiation pneumonitis was 14.6% (95% confidence interval [CI] = 5.6% to 29.2%). For patients 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 mean time to develop radiation pneumonitis in patients treated concurrently with RT and paclitaxel was statistically significantly shorter in patients receiving paclitaxel weekly than in those receiving it every 3 weeks (P =.002).

The use of paclitaxel and RT in the primary treatment of breast cancer should be undertaken with caution. Clinical trials with the use of combination CT, including paclitaxel plus RT, whether concurrent or sequential, must evaluate carefully the incidence of radiation pneumonitis.