Central reporting of human epidermal growth factor receptor-2 (HER2) status and adherence to testing and adjuvant trastuzumab treatment guidelines in Ontario.

Abstract

166 Background: Quality monitoring pertaining to trastuzumab treatment requires knowledge of 1) HER2 status, 2) testing methods and sequence, and 3) treatment received. We examined the patterns of HER2 test documentation for early-stage breast cancer (ESBC) patients in Ontario and the adherence of practice patterns to Canadian HER2 testing consensus guidelines and adjuvant trastuzumab treatment guidelines from Cancer Care Ontario (CCO). Methods: Using tumor pathology reported centrally to the Ontario Cancer Registry (OCR) a population-based retrospective cohort of ESBC patients diagnosed in 2006 or 2007 was identified. We evaluated the use of subsequent HER2 fluorescence in situ hybridisation (FISH) after initial immunohistochemical testing, and predictors of trastuzumab use. HER2 test type, sequence, result(s) and status, tumour grade, and hormone receptor status were determined. Trastuzumab treatment was determined from linked drug funding records. Sociodemographic characteristics, prior surgical, radiation and anthracycline treatment, and comorbidity were also determined from administrative data sources. Logistic models estimated adjusted odds ratios for factors associated with guideline (non-)adherence. Results: A HER2 test was documented for 66% of the 13,396 patient cohort. HER2 equivocal tumors were more likely to be retested vs. positive: OR 116 (95% confidence interval [CI] 79, 169). Patients diagnosed with stage III disease had higher odds of having a FISH test vs. stage I (OR 1.5 [CI 1.1, 2.1]). HER2 status was the largest predictor of trastuzumab use, with HER2 equivocal, negative or unknown patients less likely to receive treatment than positive. Patients with advanced age (≥70y) had lower odds of trastuzumab treatment compared to younger patients (OR 0.48 [0.32, 0.73]). Higher tumor grade was associated with higher odds of treatment. Reporting, testing, and treatment all varied significantly by region. Conclusions: Despite limitations in centrally-reported tumour pathology at the time, the use of FISH testing and trastuzumab treatment in Ontario was largely consistent with guidelines, though practices vary across regions.