855 Risk of Surgical Site Infection due to Chemotherapy and Radiotherapy in Patients Undergoing Mastectomy

Sunday, March 21, 2010
Grand Hall (Hyatt Regency Atlanta)
Margaret A. Olsen, PhD, MPH , Washington University School of Medicine, Saint Louis, MO
Kelly E. Ball, MPH , Washington University School of Medicine, Saint Louis, MO
Victoria J. Fraser, MD , Washington University School of Medicine, Saint Louis, MO
Background: Chemotherapy is assumed to increase the risk of surgical site infection (SSI) due to immunosuppression. Breast cancer patients undergoing mastectomy are often exposed to chemotherapy before (neoadjuvant) and after (adjuvant) surgery. In the last decade, use of adjuvant radiotherapy has also increased in mastectomy patients.

Objective: To determine the impact of neo- and adjuvant chemotherapy and adjuvant radiotherapy on risk of SSI after mastectomy alone or with immediate implant reconstruction.

Methods: We performed a prospective cohort study of all breast cancer surgery patients at a tertiary care academic medical center from 8/2005 – 12/2007. Mastectomies were identified from operative logs. The study population was restricted to patients with invasive or in situ breast cancer. Data were collected from the original surgical admission and all hospital readmissions and surgery and oncology clinic visits within one year of surgery. Follow-up data included signs and symptoms of SSI and noninfectious complications, microbiology cultures, additional surgical procedures, and chemo- and radiation therapy dates. Univariate analyses were performed using chi-square tests and Kaplan-Meier (KM) survival plots. An extended Cox proportional hazards model was used to determine independent risk factors for SSI, with adjuvant radiotherapy included as a time-dependent covariate.

Results: 587 patients had a mastectomy and 77 SSI were identified within one year after surgery (13.1%).  In univariate analysis, previous radiotherapy was associated with significantly increased odds of SSI (OR 3.7, 95% CI: 2.0-7.0) but neoadjuvant chemotherapy was not associated with SSI risk (OR 0.8, 95% CI: 0.4-1.5). Adjuvant chemo- and radiotherapy were not significantly associated with SSI risk in KM survival plots (log-rank P = .157 and P = .211, respectively), although adjuvant therapy violated the assumption of proportional hazards. In multivariate time to event analysis, independent risk factors for SSI included implant surgery (HR 4.4, 95% CI: 2.6-7.5), previous radiotherapy (HR 4.1, 95% CI: 2.4-7.3), body mass index 35-40 (HR 2.3, 95% CI: 1.3-4.3), body mass index > 40 (HR 4.2, 95% CI: 2.2-7.9), and adjuvant radiotherapy. At any given day after surgery, radiotherapy was associated with a 0.2% increased risk of SSI (P = .047). The increased risk of SSI associated with adjuvant radiotherapy occurred late after surgery (> 150 days). Recent or current smoking was marginally associated with increased risk of SSI (HR 1.7, 95% CI: 1.0-3.0).

Conclusions: Previous radiotherapy in mastectomy patients increased the risk of SSI four-fold. Adjuvant radiotherapy was associated with a very small risk of SSI, but only late after surgery. Neo- and adjuvant chemotherapy were not associated with increased risk of SSI after mastectomy with or without immediate breast implant reconstruction.