Mutations in the epidermal growth factor receptor (EGFR) gene in triple negative breast cancer: possible implications for targeted therapy

Abstract

IntroductionTriple negative breast cancer is associated with poorer prognosis and unresponsiveness to endocrine and anti-HER2 directed agents. Despite emerging data supporting the use of polyADP-ribose polymerase (PARP) inhibitors, complete and durable responses are rare and exploration of additional targeted therapies is needed. Epidermal growth factor receptor (EGFR) is expressed in triple negative breast cancer and several clinical trials are testing the role of anti-EGFR directed therapy. However, the rate of EGFR mutations is poorly defined. We, therefore, sought to characterize EGFR mutations in triple negative breast cancers.MethodsSeventy samples were randomly chosen from a cohort of 653 triple negative breast tumours for EGFR mutation analysis. These samples were immunostained for EGFR protein expression and consisted of negatively stained and positively stained cases. DNA was extracted from paraffin blocks and polymerase chain reaction was performed to amplify exon regions 18 to 21 of the EGFR gene. Direct sequencing of the purified PCR products was performed.ResultsEGFR mutations were found in 8 of 70 samples (11.4%). Mutations were predominantly exon 19 deletions (4 of 70 samples, 5.7%), which clustered in the region spanning codons 746 to 759 within the kinase domain of EGFR. Two types of exon 19 deletions were seen: a 15 nucleotide deletion (del E746-A750) (2 of 70 samples) and a 24 nucleotide deletion (del S752 - I759) (2 of 70 samples). Other exon 19 mutations observed were the inversion of the complementary strand (1 of 70 samples). Exon 21 mutations included missense substitution, L858R (1 of 70 samples) and T847I (2 of 70 samples). Mutations observed were independent of EGFR protein expression determined by immunohistochemical staining.ConclusionsThis study is among the first to document the presence and estimate the prevalence of EGFR mutations in triple negative breast cancer. These findings have potential implications for the design of clinical trials involving anti-EGFR directed therapy which currently do not select for patients based on presence of activating EGFR mutations, which may hence be underpowered to detect significant benefit in unselected populations. More complete sampling of EGFR mutation status in triple negative breast cancer is needed to determine the true mutation rate.

High EGFR gene copy number predicts poor outcome in triple-negative breast cancer

“…Of the four cases with EGFR mutation, three carried a missense mutation of exon 21 (L858R), one of which with a coexisting 34 so the presence of L858R and G719A mutations in this study population suggests gefitinib or erotinib therapy may be beneficial in these selected triplenegative breast cancer patients. In our study, there was disagreement between EGFR immunostaining and the presence of EGFR mutation, similar to the report of Teng and colleagues, 16 suggesting that positivity in EGFR IHC cannot predict EGFR mutation in triple-negative breast cancer. In this study, high EGFR copy number was significantly associated with poor disease-free survival and acted as an independent poor prognostic factor.…”

“…11,17,19,25,26 However, Teng et al reported the presence of EGFR mutation, specifically exon 19 deletions and exon 21 missense (L858R) mutations, in 11% (8/70) of triple-negative breast cancer samples from predominantly Chinese patients. 16 In this study, EGFR mutation was found in 3% (4/151) of triplenegative breast cancer samples from Korean patients. As suggested by Lamy and Jacot, 33 wide variations in the rate of EGFR mutation in different populations may reflect geographic or ethnic differences in the presence of EGFR mutation.…”

“…[9][10][11][12][13][14][15][16][17][18][19][20] In this study, we used EGFR pharmDx TM (Dako), which is an approved anti-EGFR antibody for identification of colorectal cancer patients eligible for treatment with cetuximab or panitumumab. Moderate to strong membranous staining in 410% of tumor cells was regarded as EGFR overexpression and was found in 97 (64%) of 151 triple-negative breast cancer cases, comparable to previous studies.…”

“…8 EGFR is a well-established treatment target for colorectal cancer, non-small cell lung cancer, and squamous cell carcinoma of the head and neck. In breast cancer, EGFR overexpression has been reported in up to 78% of triple-negative breast cancers, [9][10][11][12][13][14][15][16][17][18][19][20] more than in non-triple-negative breast cancers, 12,15 suggesting that EGFR is a potential therapeutic target for triple-negative breast cancer. EGFR tyrosine kinase inhibitors have yielded insignificant response rates in breast cancer, [21][22][23] possibly due to the lack of patient selection in these studies; they were not restricted to breast cancers with EGFR overexpression or triple-negative breast cancers.…”

“…10,11,13,14,19,25 EGFR gene mutation, another mechanism of EGFR overexpression, has been reported to be rare, 11,17,19,25,26 although a recent study reported that it was present in 11% of triplenegative breast cancers. 16 EGFR immunoreactivity has been presented as an independent indicator of poor prognosis in patients with triple-negative breast cancer. 18,20 However, there have been no reports on the prognostic impact of EGFR copy number alteration or mutation in triple-negative breast cancer.…”