Introduction. ER, PR, and HER2 are routinely available in breast cancer specimens. The purpose of this study is to contrast breast\ncancer-specific survival for the eight ER/PR/HER2 subtypes with survival of an immunohistochemical surrogate for the molecular\nsubtype based on the ER/PR/HER2 subtypes and tumor grade. Methods. We identified 123,780 cases of stages 1ââ?¬â??3 primary female\ninvasive breast cancer from California Cancer Registry. The surrogate classification was derived using ER/PR/HER2 and tumor\ngrade. Kaplan-Meier survival analysis and Cox proportional hazards modeling were used to assess differences in survival and risk\nof mortality for the ER/PR/HER2 subtypes and surrogate classification within each stage. Results.The luminal B/HER2? surrogate\nclassification had a higher risk of mortality than the luminal B/HER2+ for all stages of disease. There was no difference in risk of\nmortality between the ER+/PR+/HER2? and ER+/PR+/HER2+ in stage 3.With one exception in stage 3, the ER-negative subtypes\nall had an increased risk of mortality when compared with the ER-positive subtypes. Conclusions. Assessment of survival using\nER/PR/HER2 illustrates the heterogeneity of HER2+ subtypes. The surrogate classification provides clear separation in survival\nand adjusted mortality but underestimates the wide variability within the subtypes that make up the classification.
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