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OBJECTIVES: Prior analyses of the Occupational Disease Surveillance System (ODSS) have compared cancer rates using internal referent groups. As an exploratory analysis, we sought to estimate cancer risk using general population reference rates to evaluate the impact that the comparison population has on findings from our surveillance program. METHODS: A cohort of approximately 2.3 million workers in Ontario, Canada with an accepted lost-time workers' compensation claim were followed for all cancer diagnoses between 1983 and 2018. Standardized incidence ratios (SIRs) and 95% confidence intervals were calculated for workers in specific occupational groups using (1) all other workers in the ODSS cohort, and (2) the general population of Ontario. RESULTS: SIRs using the general population reference group were generally equal to or modestly lower compared to SIRs using the internal reference group. Within occupation groups, SIRs had a discordant direction of association (increased rate in the internal comparison and decreased in the external comparison) for some cancer sites including urinary, prostate, and colorectal. CONCLUSIONS: Findings emphasize the importance of the choice of reference group when evaluating cancer risks in large occupational surveillance cohorts. Importantly, the magnitude of confounding and the healthy worker hire bias may depend on the occupation group and cancer site of interest.
RESUMO
BACKGROUND: The relation between breast cancer molecular subtype and survival has been studied in several jurisdictions, but limited information is available for Ontario. The aim of this study was to determine breast cancer survival by molecular subtype and to assess the effect on survival of selected demographic and tumour-based characteristics. METHODS: We extracted 29â¯833 breast cancer cases (in 26â¯538 girls and women aged ≥ 15 yr) diagnosed between 2010 and 2012 from the Ontario Cancer Registry. Cancers were categorized into 4 molecular subtypes: 1) luminal A (estrogen-receptor-positive and/or progesterone-receptor-positive [ER+ and/or PR+] and negative for human epidermal growth factor receptor 2 [HER2-]), 2) luminal B (ER+ and/or PR+/HER2+), 3) HER2-enriched (ER- and PR-/HER2+) and 4) triple-negative (ER- and PR-/HER2-). We estimated associations with predictor variables (age, stage at diagnosis, histologic type, comorbidity and place of residence [urban or rural]) using a multivariate Cox proportional hazards model. Likelihood ratio testing was used to evaluate differences in risk of death. RESULTS: Luminal A was the most commonly diagnosed subtype (59.0%) and had the greatest survival, whereas triple-negative had the poorest survival. For all subtypes, a dose-response effect was observed between the hazard of death and age and stage at diagnosis, with the greatest effect found for the HER2-enriched subtype (age: hazard ratio [HR] 7.87 [95% confidence interval (CI) 3.68-11.81]; stage at diagnosis: HR 37.71 [95% CI 34.64-41.27]). Moderate comorbidity (Charlson Comorbidity Index score 1 or 2) was associated with increased risk of death for triple-negative cancers (HR 2.42 [95% CI 1.36-4.31]), and severe comorbidity (Charlson Comorbidity Index score ≥ 3) increased the risk for all molecular subtypes. INTERPRETATION: The results indicate the importance of including molecular subtype, along with age, stage at diagnosis and comorbidity, in assessing breast cancer survival. They highlight the need to address outcomes related to hormone-receptor-negative cancers, for which survival lags behind that for hormone-receptor-positive cancers.
