HER2/ERBB2 immunoreactivity in human retinoblastoma

Abstract

Retinoblastoma (RB) is an ocular malignancy of early childhood. Although mutations in the Rb1 gene and expression of stem cell markers have been identified in RB, additional information on RB-specific alterations in signaling pathways and protein expression would be useful for the design of targeted RB therapies. Here we have evaluated the expression of HER2 (ERBB2) in RB. HER2 is a member of the epidermal growth factor family, which is overexpressed in breast, ovarian, gastric, colorectal, pancreatic, and endometrial cancers in a stratified manner. Overexpression and gene amplification of HER2 is associated with aggressive malignancies, accompanied by chemoresistance and poor outcomes. In this study, we present the first evidence of HER2 immunoreactivity in retinoblastoma, as shown by immunocytochemistry, flow cytometry, and western immunoblot, with validation by reverse transcription PCR (RT-PCR) in both RB cell lines and clinical RB tumors. Our results suggest that the HER2 protein expressed in RB is a truncated version that spares the trastuzumab binding site, while HER2 is not detected in normal ocular tissues. Our discovery of HER2 expression in RB may lead to innovative and targeted drug treatment options designed to spare the eye and preserve vision in RB patients.

HER2 Overexpression in Retinoblastoma: A Potential Therapeutic Target

“…1 c, d). Notably, this dilution is 10 times lower than the one used by researchers who suggested positive HER2 immunoexpression in RB [22] . Since in this IHC study, we aimed to specifically stain a transmembrane protein, it would be crucial to accurately define the antibody concentration and protocol as described in the Materials and Methods section.…”

“…As previously stated, Seigel et al [22] have recently claimed that there is a truncated version of this transmembrane protein in RB tissue samples, as recognized by 214 some antibodies -including trastuzumab. These authors studied HER2 expression in various cell lines and in 11 tissue samples, which were scored from 0 to 3+.…”

“…Only a 3+ positive score is an indication for the use of HER2-directed therapies [27] . In their study, 3 (27%) of the tissue samples had a HER2 3+ score (i.e., positive), 5 (46%) had a 2+ score (i.e., equivocal), and the remaining 3 (27%) were classified with a 1+ score (i.e., negative) [22] .…”

“…Also, the antibody used was the same (Sigma-Aldrich #HPA001383). This anti-HER2 antibody binds to the intracellular protein domain and detects the truncated HER2 protein, which Seigel et al [22] postulate to be present in Rb. We used HER2-positive mammary carcinoma as a positive control.…”

“…However, Seigel et al [22] have recently claimed that significant HER2 immunoreactivity may be present in RB cell lines and in a small cohort of primary RB patients ( n = 11). The authors suggested that a truncated version of the HER2 protein was present in RB, and only a few anti-HER2 antibodies could recognize this version.…”