Résumé
Background: Triple negative breast cancer (TNBC) is characterized by the lack of expression of hormone receptors and HER-2 antigen. This lack of drugs targets prompted the search for additional targeted therapies. The transmembrane EGFR receptor, also known as HER1, and the phosphatidylinositol 3 phosphate kinase (PI3K) appears frequently dysfunctional in TNBC. It thus appears important to simultaneously evaluate these biomarkers of interest in order to better characterize this population of tumors and the opportunity of dedicated biomarkers-oriented targeting in a European population of TNBC patients.
Material and methods: A total of 1,695 consecutive patients with breast cancer referred to the Val d’Aurelle Cancer Institute between 2002 and 2010 were prospectively entered into the database of a tumour DNA and cytosol biobank. 204 cases with a localized TNBC were selected for the present study.
PIK3CA PCR amplification and high-resolution melting (HRM) analysis designed to span exon 9 and 20 mutations were performed on a Rotor-Gene 6000™ using the LightCycler 480 HRM PCR Master Mix™ kit. Bidirectional sequencing was performed by using PCR primers and an Applied Biosystems 3730xl DNA Analyzer.
Regarding HER1 CNV determination, qPCR reactions were performed on an ABI Prism 7700 sequence detection apparatus. HER1 levels were normalized to ACBT and GAPDH expression. Measurements were performed in duplicate. The data were expressed as the HER1/ACBT or HER1/GAPDH relative copy number ratio. EGFR cystosol quantification was performed with EGFR Elisa Kit (Calbiochem). Proteins were quantified with the pierce method. Results were expressed in nmol/mg of protein.
Results: Regarding the PIK3CA gene, we identified 14 (6.9%) mutations in exon 9 and 17 (8.3%) mutations in exon 20. Exon 9 mutations were associated with SBR grade I-II (p=0.04) and exon 20 mutations were associated with size 3-4 (p=0.03). Overall mutations were only associated with SBR I-II (p=0.05). HER1 gene was deleted in 11 cases (5.3), normal in 154 cases (75.9%), amplified in 18 cases (8.9%) and presented a polysomy in 20 cases (9.9%). HER1 amplification was clearly associated with an increased EGFR protein content (p=0.03), while polysomic cases presented an EGFR content non-significantly different of the normal HER1 cases. After a median follow-up of 5.6yrs, the 5-year Disease Free Survival ( DFS) rate was 76.1% (95% CI [69.2; 81.6]) and the 5-year Overall Survival (OS) rate was 81.3% (95% CI [74.8; 86.3]). PI3KCA exon 9 mutations were a significant pejorative prognostic factor in univariate and multivariate analysis, while a high (upper quartile) EGFR protein content was associated with a better prognosis, in uni- and multivariate analysis.
Conclusions: In this large cohort of localized TNBC, 15.2% of patients presented mutations in both exon 9 or 20 of PI3KCA, and 8.9% of the tumors presented HER1 amplification. Our study shows the negative prognosis value of exon 9 PI3KCA mutations. We confirm then the clinical importance to detect PI3KCA mutations in TNBC. In addition, a high EGFR tumoral content was associated with a better prognosis. The exact mechanism of this association warrant further studies.
Citation Format: William Jacot, Caroline Mollevi, Anne-Claire Laberenne, Nicolas Lozano, Catherine Viglianti, Frédéric Bibeau, Gilles Romieu, Pierre-Jean Lamy. Prognostic value and clinicobiological associations of the EGFR / PI3K pathway in 204 consecutive localized sporadic triple negative breast cancers [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-06-05.