The Prognostic Impact of BRCA1 Protein Expression in Patiens with Non-small Cell Lung Cancer

Introduction: BRCA1 is a 220kDa multifunctional protein which has recently gained a major scientific interest as a potential prognostic and/or predictive marker for various tumors, including non-small-cell lung cancer (NSCLC). Overexpression of BRCA1 mRNA has been associated with poor survival in chemonaive, stage IB and in advanced stage NSCLC patients after DNA damaging chemotherapy. These findings are not confirmed by immunohistochemistry which is more reliable and widely used tool for diagnostic purposes. On the other hand only mRNA expression does not reflect the presence of full length, functional protein.

Aim: We aimed to investigate the prognostic impact of BRCA1 immunohistochemical expression in NSCLC patients, using different antibodies.

Material and methods: We tested five antibodies (Abcam). Three of them against different parts of BRCA1 proten: MS110 against N-terminal (1-304aa), GLK2 against C-terminal (1832-1863aa) and 17F8 against central (762-1315aa) part of BRCA1. Also, two antibodies against phosphorilated forms of BRCA1 at Ser1423 (phosporilated during normal cellular functioning of BRCA1 and also in response to DNA damage) and Ser1524 (specifically phosphorylated by ATM in response to DNA damage). After testing several antigen retrieval methods GLK2 and 17F8 were excluded from the study. We performed BRCA1 immunohistochemistry on tissue microarrays (TMAs) composed of 104 early (I,II stage) and advanced (III, IV stage) NSCLCs. Patients with III and IV stage disease were treated by adjuvant cisplatin-based chemotherapy. Staining results were statistically analyzed in correlation with all available clinicopathological characteristics.

Results: BRCA1 MS110 staining showed extremely weak nuclear positivity in 28% of NSCLC cases, 82% were positive for Ser1423 and only 27% for Ser1524 antibody. Statistical analysis of data showed no significant correlation between BRCA1 MS110 and Ser1423 expression with respect to clinicopathological data. Only BRCA1 Ser1524 nuclear positivity was significantly correlated with longer overall survival (OS) and disease free survival (DFS) in stage I and II patients (p<0,001), whilst OS and DFS were shorter in S1524 positive stage III and IV patients (p=0,001).

Conclusions: (1) The discrepancy between BRCA1 mRNA and protein study results might be due to the BRCA1 protein nature and inability to detect the full length, functional protein; (2) BRCA1 phosphorylaton, at least in ser1524, differently determines the prognosis of early and advanced NSCLC, supposedly due to its role in DNA repair. (3) The detection of phosphorilated forms of BRCA1 might serve as useful prognostic marker for patients with NSCLC.

This publication was supported by a grant IGA MZ CR NS/9959-3, project BIOMEDEG C.1.05/2.1.00/01.0030, GACR 303/09/HO48, LF_2010_006.