Copy Number Variation of the PI3K/AKT Pathway Genes in Triple Negative Breast Cancer

Abstract

INTRODUCTION: Triple negative (TN) breast cancer is a biological group of tumors that lack the expression of estrogen (ER) and progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). These tumors are associated with poor prognosis and a high mortality rate when compared to other breast cancer subtypes. The phosphatidylinositol 3-kinase (PI3K/AKT) signaling pathway mediates key cellular functions such as cell growth, proliferation and survival. Frequent deregulation and aberrations of this pathway have been implicated in breast cancer development and in therapy resistance. Thus, multiple drugs targeting the PI3K/AKT pathway are in development and are been tested in clinical trials as single and/or in combination with other therapies in TN patients. METHODS: In this study, specific genes involved in PIK3/AKT pathway, PIK3CA, AKT1, AKT2, PTEN and FGFR2, were analyzed for DNA copy number changes in samples of triple negative (TN) and non-triple negative breast tumors (N-TN) using the array-CGH, real time PCR and FISH methodologies. A total of fifty-four samples of TN breast cancer were obtained from the Nossa Senhora das Gracas Hospital, Curitiba, PR, Brazil, and sixty-five samples of N-TN tumors from the University of Western Cape, Cape Town, South Africa. RESULTS: Epidemiological studies performed with the clinical-pathological data of these patients (age, tumor size, histological grade and lymph node status) showed a significantly higher frequency of grade III tumors and lower frequency of grade I tumors in TN when comparing with N-TN patients. This association was also observed when data of TN Brazilian patients were compared with N-TN patients from the same region of Brazil, corroborating previous studies that associated the TN phenotype with features of poor prognosis. DNA copy number changes were observed in all the five genes studied and PTEN loss was the most frequently alteration in both TN and N-TN cases. In addition, the analyses between copy number alterations and clinical-pathological parameters of patients showed that PTEN loss was significantly associated with advanced tumor grade (III) in the TN subtype. When the copy number changes of the five genes were compared between TN and N-TN cases, the high copy number of FGFR2 gene was significantly associated with TN tumors. These findings corroborated previous studies that associated FGFR2 gene amplification with TN phenotype, suggesting that alterations in this gene may be used as an important prognostic factor and possible therapeutic target for TN tumors. The frequencies of AKT1, AKT2, PIK3CA and PTEN alterations did not differ significantly between the two subtypes of tumors studied and therefore may play a role in the development of both tumor subtypes. CONCLUSIONS: DNA copy number changes in genes of the PI3K/AKT signaling pathway are frequent and present relevance for breast tumors with the TN phenotype. Alterations in some of these genes were significantly associated with poor prognosis markers, such as advanced tumor grade. Once these alterations are validated in a new and independent set of TN patients, their value as prognostic markers and their potential use as therapeutic targets can be established.