The prognostic effect of HER2 heterogeneity and YAP1 expression in HER2 positive breast cancer patients: a retrospective study.

Background: This study sought to estimate the prognostic effect of intratumoral heterogeneity (ITH) and Yes-associated protein 1 (YAP1) intensity in human epidermal growth factor receptor 2 (HER2) positive breast cancer patients. We also investigated individualized adjuvant therapy for YAP1-sufficient patients and HER2 heterogeneous patients.

Methods: The relationship between prognostic outcomes and clinicopathological variables in 1,650 retrieved breast cancer patients was evaluated. The HER2 intensity and YAP1 expression in HER2-ITH and non-ITH (NITH) patients were also estimated. All patients were followed-up, regardless of whether or not they received intensive treatment, to explore individualized adjuvant therapy for YAP1-sufficient patients and HER2 heterogeneous patients.

Results: Over-expression and nuclear localization of YAP1 were significant in HER2-ITH patients. The over-expression of YAP1 and the presence of ITH affected the prognosis of HER2 positive patients. YAP1 intensity and lymph nodes metastases was more obviously affected the survival of HER2-ITH patients, while the prognosis of NITH patients were correlated with clinical Tumor-Node-Metastasis (cTNM) stage and lymph-vascular space invasion (LVSI) status. HER2-NITH patients and YAP1-insufficient patients benefited from a combination of Trastuzumab and Pertuzumab/Lapatinib, while Capecitabine significantly decreased the relapse risk of ITH patients and YAP1-sufficient patients.

Conclusions: YAP1 overexpression and nuclear localization was usually observed in HER2-ITH patients. For HER2-NITH patients, an advanced stage of cTNM and LVSI status increased the recurrent risk, and intensified Pertuzumab or Lapatinib treatment (combination with Trastuzumab) improved their survival. For HER2-ITH patients, the overexpression of YAP1 and pathological lymph nodes (pLN) metastases increased recurrent risk, and intensified Capecitabine treatment improved their survival. YAP1 overexpression contributed to a poor prognostic outcome, especially when HER2 signal intensity was insufficient.