Abstract
617 Background: There is increasing recognition of the existence of intratumoral heterogeneity of the human epidermal growth factor receptor (HER2), which affects interpretation of HER2 positivity in clinical practice and may have implications for patient prognosis and treatment. Only patients (pts) with HER2 positivity - defined as 3+ by IHC or FISH amplified defined as a HER2 gene to chromosome 17 (HER2/CEP17) ratio ≥ 2.0 - are eligible to receive trastuzumab treatment. Limited information is available on the prognosis of pts with HER2 2+ or FISH test with a HER2/CEP17 ratio < 2.0. Methods: We retrospectively analyzed data from 455 consecutive early BC pts with HER 2+ and HER2/CEP17 ratio < 2.0 who underwent surgery after 2007. The association between HER2/CEP17 ratio and other known prognostic factors was evaluated with multivariable linear regression models. The role of HER2/CEP17 ratio on recurrence free survival was assessed with multivariable Cox regression models. Results: Fifty-one percent of the evaluated pts were node negative, 51% were postmenopausal, 93% had ER positive BC and 85% had Ki-67 ≥14%. The mean HER2/CEP17 ratio was 1.27 (SD=0.3). A significant positive relationship between HER2/CEP17 ratio and Ki-67 was observed (p<0.01). During a median follow-up time of 2.7 years, 40 recurrences were observed (15 locoregional events and 25 distant metastases). Overall, the association between HER2/CEP17 and the risk of recurrence was not significant. From subgroup analysis, a significant interaction between HER2/CEP17 ratio and nodal involvement emerged (p=0.02). Among pts with node-negative disease, pts with HER2/CEP17 ratio ≥1.27 were at higher risk of recurrence with respect to pts with HER2/CEP17 ratio < 1.27 (adjusted HR 4.0, 95% CI 1.01-15.9). Conclusions: Among pts with BC and HER2 intratumoral heterogeneity, HER2/CEP17 ratio ≥1.27 could have a strong prognostic role in node negative HER2 2+ BC, thus suggesting potential future therapeutic approaches in this setting of pts.
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