Background: HER2-positive breast cancer is an aggressive tumor subtype and it is usually associated with worse clinical outcomes. Given the advances in HER2-targeted therapies, we hypothesized that HER2 amplification is no longer a marker of poor prognosis.
Methods: We conducted a population-based observational study employing two independent cohorts of patients with breast cancer. Samples from the METABRIC cohort were collected before clinical availability of HER2-targeted therapies, whereas samples from the SCAN-B cohort were collected afterward. The primary endpoint was overall survival (OS).
Results: A total of 5121 patients were included in the analyses. In both cohorts, HER2-positive tumors were more likely to be node-positive (P < .05) and high grade (P < .001). Before HER2-targeted agents, HER2 patients had a significantly worse 5-year OS than hormone receptor-positive (HR+) patients (63.4% vs. 83.0%, HR = 2.49, P < .001). In contrast, after HER2-targeted agents entered clinical practice, 5-year OS no longer differed (88.3% vs. 90.4%, HR = 1.24, P = .17). Additionally, in an exploratory analysis using PAM50 subtypes, we identified that, after HER2-targeted therapies were implemented, patients clinically HER2-negative but PAM50-HER2-enriched have a lower OS (HR = 1.99, P = .009) than those who are both HER2-positive and PAM50-HER2-enriched, since they have not benefitted from HER2-targeted therapies.
Conclusions: HER2-targeted therapies dramatically altered the natural history of HER2-positive breast cancer, with overall survival approaching those of luminal subtype. HER2 positivity is no longer a marker of poor prognosis if access to HER2-targeted therapies is granted. Future trials should assess whether HER2-negative PAM50-HER2-enriched patients may also benefit from such therapies.
Keywords: Mortality; PAM50; Prognosis; Trastuzumab; erbb2.
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