Phosphorylation of EGFR measured with in situ proximity ligation assay: Relationship to EGFR protein level and gene dosage in cervical cancer

Purpose We have applied the sensitive and specific in situ proximity ligation assay (PLA) to characterize Tyr1068 phosphorylation of the epidermal growth factor receptor (EGFR) in cervical cancer in relation to the protein level and gene dosage. Materials and methods Pretreatment tumor biopsies from 178 patients were analyzed. EGFR protein level was determined by immunohistochemistry, and Tyr1068 phosphorylation was detected with PLA in 97 EGFR positive tumors. EGFR gene dosage was derived from array comparative genomic hybridization of 86 cases. Results EGFR was expressed in most tumors, whereas phosphorylation was seen in about half of the EGFR positive ones. A correlation was found between the expression of EGFR and phosphorylated EGFR ( p =0.016, membrane; p =0.012, cytoplasm). However, tumor regions with high protein level without phosphorylation were occasionally seen and the percentage of EGFR positive cells was higher than the phosphorylated percentage ( p p =0.014) and cytoplasm ( p =0.002) was seen in 11 tumors with gain of EGFR. The protein level was not correlated with gene dosage. Conclusion In contrast to gain of the EGFR chromosomal region, high EGFR protein level may not necessarily indicate Tyr1068 phosphorylation and thereby receptor activation in cervical cancer.