Increased expression and activity of Akt in primary ductal breast cancers and activation of the ErbB2/Akt/ER- α pathway

3575 Introduction: We have previously demonstrated that Akt1 is activated not only by epidermal growth factor (EGF), insulin-like growth factor I (IGF-I), and heregulin-β1 (HRG-β1), but also by estradiol. This cross-talk between growth factors and estrogen receptor-α (ER-α) signaling converges in the EGF receptor family member, ErbB2 / phosphatidylinositol 3-kinase PI 3-K/serine/threonine protein kinase Akt pathway in hormone-dependent MCF-7 breast cancer cells in vitro and xenografts grown in vivo. The aim of the present study was to investigate whether the current model of this tumorigenic pathway is active in clinical breast cancer. Methods: We analyzed the expression levels of Akt1 and phosphorylated Akt (pAkt) by immunohistochemistry and western blot analysis in pairs of frozen tumor samples and their corresponding matched normal adjacent lobular breast tissue from 58 breast cancer patients. These patients did not have a previous history of therapeutic intervention. The tumors were mostly invasive, high grade, ductal carcinomas, with an approximately equal distribution of ER-α, ErbB2, and lymph node positivity. Spearman’s rank correlations were calculated for Akt expression and phosphorylation, measured by either immunohistochemistry or western blot, and patient and clinical-pathological tumor classification. Results: Marked staining was observed for Akt1 in 98% of the tumors and pAkt was expressed in 83%. Akt1 was localized mostly in the cytoplasm, but also in the nucleus. Normal tissues revealed much less staining for Akt1 and pAkt than tumor tissue, also with more cytoplasmic localization and less nuclear staining. Nuclear Akt1 measured by immunohistochemistry was highly correlated with Akt1 expression measured by western blot analysis (Akt-WB) (p=0.04), cytoplasmic Akt1 (cyt Akt) (p=0.006), and nuclear pAkt (p=0.003). Additionally, nuclear pAkt was highly correlated with phosphorylated cytoplasmic Akt (cyt pAkt) (p=0.001). Akt1 and pAkt expression were not significantly correlated with age, tumor type, nuclear grade, lymph node positivity, progesterone receptor (PR), or the proliferation rate, Ki67. Nuclear Akt1 and cyt pAkt were each significantly correlated with tumor size (p=0.02). Cyt pAkt was positively correlated with histological grade (p=0.02) and inversely correlated with ER-α status (p=0.04) and with ErbB2 expression (p=0.05). Nuclear pAkt was also inversely correlated with ErbB2 (p=0.04). pAkt measured by western blot (pAkt-WB) was also associated with tumor size (p=0.03). Conclusion: Similar to our in vitro model and animal data, in invasive, high grade, ductal carcinomas, Akt expression and activity is high and correlates with ErbB2 and ER-α expression, histological grade, and tumor size.