Global Profiling of EGFR Gene Mutation, Amplification, Regulation and Tissue Protein Expression in Unknown Primary Carcinomas: to Target or Not to Target?

Introduction: Epidermal growth factor receptor (EGFR) signalling contributes to malignant transformation and survival. We studied molecular predictors of benefit from EGFR-modulating therapies in patients with cancer of unknown primary (CUP).

Materials And Methods: Tumours from paraffin-embedded biopsies of 50 patients with CUP were stained for EGFR protein by immunohistochemistry. Polymerase chain reaction amplification, single-strand conformational polymorphism and direct sequencing were used to study EGFR intron 1 cytosine-adenosine (CA) repeat length as well as exon 18, 19, 21 activating mutations and amplification.

Results: Thirty-seven tumours (74%) expressed EGFR protein but only six (12%) strongly. Regarding intron 1 CA repeat length, we detected five alleles with CA repeat numbers 16-20, allele 16 being the most common (39%). All samples were heterozygous, the commonest genotype consisting of 16/18 dinucleotides (78%). Five samples had three intron 1 alleles and were associated with EGFR overexpression in 40% of cases. There was no evidence of EGFR exon 18, 19, 21 amplification. Two mutations were detected: Exon 21 2508 C > T, a silent nucleotide polymorphism (R836R) and a G > A substitution in sequences flanking exon 19 (IVS19 + 24G > A) resulting in aberrant mRNA splicing. Neither EGFR protein expression nor CA repeat length were prognostic factors for survival.

Conclusions: Our data depict absence of molecular predictors of benefit from EGFR modulation in patients with CUP. Study of its molecular pathophysiology and targeting other molecular pathways may be warranted instead.