Use and impact of chemotherapy-free intervals in metastatic colorectal cancer in routine practice.

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6535 Background: Several randomized trials have shown that chemotherapy-free intervals (CFIs) may reduce toxicity without compromising survival in patients with metastatic colorectal cancer (mCRC) treated with non-curative intent. However, uptake and outcomes of this approach in routine practice are unknown. We performed a population-based study of the patterns of use of CFIs and their impact on survival and toxicity among patients treated with first-line intravenous (IV) chemotherapy in Ontario, Canada. Methods: The Ontario Cancer Registry was linked with several other administrative databases to identify patients with colorectal cancer who started first-line IV chemotherapy between 2007-2009. A patient was considered to have had a CFI if more than 56 days elapsed between two chemotherapy billing claims. Survival of patients who had at least one CFI was compared to those who did not using Cox regression stratified by duration of treatment and adjusted for age, sex and Charlson comorbidity score. Analysis was performed separately for each type of first line treatment: Irinotecan (IRI), Irinotecan plus Bevacizumab (IR+B), and Oxaliplatin (OX). Toxicity was estimated by calculating the rate of emergency department visits and hospitalizations (adjusted for time on treatment) between those who did and did not have chemo breaks. Results: Between 2007-2009, 1,989 patients started first-line chemotherapy for mCRC in Ontario (22.6% IRI, 47.9% IRI+B, 29.5% OX). 489 (24.6%) had at least one CFI (14.9% IRI, 33.2% IRI+B, 18.1% OX). The median duration of first line treatment was 205 days (IQR 107-366 days). The median duration of the first CFI was 127 days (IQR 90-234 days). In multivariate models stratified by duration of treatment, CFIs did not have a negative effect on survival in either of the 3 treatment groups (HR: 0.62 IRI, 0.90 IRI+B, 0.51 O). Toxicity was lower in patients who had at least one CFI (12.6 vs 16.8 ER visits or admissions per person-month, p=0.036). Conclusions: Chemo-free intervals are used in routine practice in Ontario, and are associated with lower toxicity, without any apparent evidence of negative impact on survival.