Smoking History as a Predictor of Secondary Malignancy Among Prostate Brachytherapy Patients

Abstract

To report the impact of smoking history and excess risk of secondary malignancy (SM) in patients undergoing brachytherapy for prostate cancer. Between 1998 and 2008, 1,092 patients with localized prostate cancer were treated with brachytherapy alone (n = 687) or combined with external beam radiation therapy (EBRT) (n = 405). The smoking history and subsequent diagnosis of SM were recorded for each patient. In-field SM included bladder and rectal cancer; out-of-field cancers included any SM outside the pelvic region. The median age of the cohort was 66 years. Predictors of SM explored included age, radiation modality, dose, use of androgen deprivation therapy (ADT) and smoking history. The Kaplan-Meier method was used to determine the actuarial likelihood of developing a SM, and multivariate analysis was done with Cox Regression. With a median followup of 47.5 months (range: 3-134), there were 69 SM diagnoses. Multivariate analysis revealed smoking packyear was the only significant predictor for the development of any SM (p = 0.003), as well as infield SM (p = 0.035) and out-of-field SM (p = 0.05). There was no significant association between SM risk and radiation modality, dose, or use of ADT. There was a correlation with extent of smoking exposure and risk of SM. The 10-year likelihood of SM development was 36% with greater than 20 packyears, while it was 12% with less than 20 packyears. The 10-year mortality rate related to SM generally was 10.8% for patients with greater than 20 packyears, while it was 1.5% for patients with less than 20 packyears. The risk of secondary malignancy incidence and mortality following brachytherapy for prostate cancer is strongly correlated to extent of smoking history. Patients undergoing brachytherapy-based treatment for prostate cancer should be strongly counseled in smoking cessation.