Postmastectomy radiation in women with node positive breast cancer in the Ontario population.

Abstract

e12104 Background: Despite two randomized controlled trials first published in 1997 showing improvements in both locoregional control and survival, postmastectomy radiation for node positive breast cancer patients has not been universally accepted; particularly for patients with 1-3 positive nodes. Subsequent favorable meta-analyses have resulted in more recent guidelines supporting postmastectomy radiation. We examined the rate and predictors of postmastectomy radiation receipt in node positive breast cancer patients in Ontario (population 13.2 million). Methods: We used the Ontario Cancer Registry, a population-based, prospectively-collected registry, to identify all node positive female breast cancer patients in the province with a diagnosis date between April 1, 2010 and Sept 30, 2014. Patient records were linked to prospectively maintained health administrative databases. Through these databases, the universal single-payer health care system in Ontario can capture details for each patient for all health care encounters, hospitalizations, procedures (mastectomy), prescription medications, systemic cancer therapy and radiation. Logistic regression modeling using generalized estimating equations was employed to determine the association between patient, tumor and treatment characteristics and receipt of radiation, while accounting for the possible clustering effect by health regions. Results: Of the 6,535 women with node positive breast cancer who had undergone a mastectomy 73.9% received radiation. Of the 4227 women with 1-3 positive nodes, 68.7% received radiation, and of the 2308 women with > 3 positive nodes 83.4% received radiation. Receipt of radiation was positively associated with younger age ( < 70 years), increasing cancer stage and a lower Charlson comorbidity index. Conclusions: In a setting with universal healthcare, the majority of women with node positive breast cancer in Ontario received postmastectomy radiation, including women with 1-3 positive nodes. Older women, those with higher stage and those who had increased co-occurring medical conditions were less likely to receive radiation therapy.