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Objectives: We evaluated adherence of human epidermal growth factor receptor-2 testing using immunohistochemistry and fluorescence in situ hybridization, as well as adjuvant trastuzumab treatment according to Canadian guidelines, and predictors of trastuzumab use in early-stage breast cancer in Ontario., Methods: Retrospective cohort of early-stage breast cancer patients identified in the Ontario Cancer Registry. Human epidermal growth factor receptor-2 test type, sequence, result(s), tumor grade, and hormone receptor status were abstracted from Ontario Cancer Registry pathology reports. Trastuzumab treatment was determined from provincial cancer agency records. Other variables were determined from administrative data sources. Logistic regression models were used to estimate adjusted odds ratios for factors associated with guideline adherence., Results: The first human epidermal growth factor receptor-2 test result was the strongest predictor of confirmatory testing ( p  < 0.05). Human epidermal growth factor receptor-2 testing by immunohistochemistry accounted for the majority of documented first tests (94%; n  = 8249). Overall, 27% ( n  = 2360) of tested patients received a second test by fluorescence in situ hybridization (46%) or immunohistochemistry (49%) assay. Most human epidermal growth factor receptor-2 equivocal patients (89%; n  = 784) received a confirmatory test. Among human epidermal growth factor receptor-2-positive patients, only 57% ( n  = 385) received trastuzumab treatment within the study period. Human epidermal growth factor receptor-2 status was the strongest predictor of trastuzumab use. Younger patients (<70 years at diagnosis) and negative hormone receptor status had higher odds of trastuzumab treatment ( p  < 0.05) compared to older and positive hormone receptor status patients., Conclusions: Immunohistochemistry use as a first test was largely consistent with Canadian guidelines; however, immunohistochemistry was frequently used as a confirmatory test, which is not guideline-concordant. Monitoring these testing and treating patterns is necessary to optimize health outcomes associated with trastuzumab.

Background: Uncertainty about human epidermal growth factor receptor-2 (HER2) testing practice in Canada continues to hinder efforts to improve personalized medicine. Pathologists routinely perform HER2 assessment for all tumors > 1 cm, and pathology is reported centrally to the provincial cancer registry., Objectives: To understand patterns of HER2 test documentation for early-stage breast cancer (BC) patients in Ontario's centralized pathology reporting system., Study Design: Retrospective cohort study of central HER2 test documentation in early-stage BC patients diagnosed in 2006-2007., Methods: Cohort and staging information was derived from cancer registry and admissions data. Linkage across administrative databases provided data on surgical and radiologic treatment, sociodemographic factors, diagnosis setting, and comorbidities. Pathology reports from the provincial cancer registry were reviewed for HER2 testing, hormone receptor, and grade. Unadjusted and adjusted odds ratios were calculated to determine factors related to HER2 documentation., Results: A HER2 test was documented for 66% of 13,396 patients. HER2 documentation was associated with stage, hormone receptor, and tumor grade documentation. Higher stage and grade at diagnosis were also associated with HER2 documentation. All models suggested variable regional documentation patterns. Documentation did not differ by sociodemographic factors, presence of comorbidities, or surgical procedure., Conclusions: Despite a universal testing policy, the rate of centralized HER2 test documentation was lower than expected and related to disease severity. Differences in regional reporting likely reflect ascertainment bias inherent to centralized pathology reporting rather than testing access. Improved HER2 reporting is encouraged for cancer registration, quality-of-care measurement, and program evaluation.