Chasing Hippos: Implications of YAP1 and TAZ Expression in Pregnancy-Associated Breast Cancer Tumorigenesis

Abstract Background: Hippo signaling pathway de-regulation has been strongly associated with tumorigenesis, metastasis, and drug resistance. Pregnancy-associated breast cancer, the most frequently diagnosed malignancy during gestation, demonstrates an intricate molecular nature. The aim of the present study is to evaluate Hippo pathway transducers TAZ and YAP1 expression in pregnancy-associated breast cancer in relation to the clinicopathological characteristics of the disease. Methods: Formalin-fixed paraffin-embedded tissues from 21 PABC patients treated at Alexandra Hospital in Athens, Greece were immunohistochemically analyzed. Statistical analysis was performed to investigate a possible correlation among the Hippo pathway signaling and the clinical features of the disease. Results: In 48% of patients included in the study strong nuclear TAZ/YAP1 staining in tumor cells was identified. Additionally, the hormone receptor negative status was statistically correlated with strong positivity of the TAZ/YAP1 co-transcriptional factors. No association was observed with the overall-survival and the disease-free survival rate. Conclusions: Hippo pathway is proven to be de-regulated in a subset of pregnancy-associated breast cancer patients highlighting the complex molecular background of the disease which certainly requires further investigation.