IMPORTANCE Optimal chemotherapy dosing in obese patients remains uncertain, with variation in practice. Dose reduction strategies are often used to avoid chemotoxicity, but recent American Society of Clinical Oncology guidelines recommend full dose. OBJECTIVE To evaluate the impact of body mass index (BMI) on chemotherapy dosing and of dose reduction on ovarian cancer survival. DESIGN, SETTING, AND PARTICIPANTS Cohort study in Kaiser Permanente Northern California (KPNC) health care setting of patients with primary invasive epithelial ovarian cancers diagnosed from January 2000 through March 2013. Analyses focused on 806 patients receiving adjuvant first-line therapy of carboplatin and paclitaxel with curative intent. MAIN OUTCOMES AND MEASURES Overall and ovarian cancer-specific mortality. Deaths were identified through the KPNC Mortality Linkage System, with median follow-up of 52.5 months. Hazard ratios (HRs) and 95% CIs were estimated from proportional hazards regression, accounting for prognostic variables including age at diagnosis, race, stage, grade, histologic type, chemotoxic effects, comorbidities, cancer antigen 125 levels, and BMI at diagnosis. RESULTS The strongest predictor of dose reduction was a high BMI. Compared with normal-weight women, obese class III women received 38% and 45% lower doses in milligrams per kilogram of body weight of paclitaxel and carboplatin, respectively (P <.001 for each agent). They also received lower relative dose intensity (RDI) for each agent and the combined regimen, calculated as average RDI (ARDI). Mean ARDI was 73.7% for obese class III women and 88.2% for normal-weight women (P <.001). Lower ARDI (<70%) was associated with worse overall (HR, 1.62 [95% CI, 1.10-2.37]) and ovarian cancer-specific survival (HR, 1.69 [95% CI, 1.12-2.55]). Women who were obese at diagnosis appeared to have better survival. In multivariable-adjusted analyses considering joint effects by BMI and ARDI, compared with women with normal weight and no dose reduction, normal-weight women with dose reduction (ARDI < 85%) experienced worse survival (HR, 1.50 [95% CI, 1.02-2.21]). For each BMI category, those with ARDI less than 85% had worse survival than those without dose reduction. The improved survival among obese women was no longer apparent with dose reduction. CONCLUSIONS AND RELEVANCE Lower RDI was an independent predictor of ovarian cancer mortality. This finding was strongest among normal-weight women but seen at all levels of BMI. Our results suggest that body size should not be a major factor influencing dose reduction decisions in women with ovarian cancer.
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