Endocrine Abstracts

Introduction: Adrenocortical carcinoma (ACC) is a rare, aggressive tumour with unsatisfactory treatment options in advanced disease. Activation of epithelial to mesenchymal transition (EMT) has been described as causative of metastatic spread in a variety of human cancers. Accordingly, new drugs were developed specifically targeting EMT with a focus on HGF/c-MET and FGF/FGFR signalling. We here asked whether EMT is a relevant mechanism in ACC.

Methods: Expression of epithelial and mesenchymal markers was assessed in 20 normal adrenal glands (NAG), 23 adrenocortical adenomas (ACA) and 27 ACC. Epithelial marker E-cadherine and mesenchymal markers SLUG and N-cadherine were analysed by IHC. Expression of FGFR1-4 was quantified in FFPE tumour tissue using RNAscope and qRT-PCR array was employed to quantify expression of 92 FGF-FGFR pathway genes. Isoform switching between isoforms IIIb (epithelial) and IIIc (mesenchymal) characteristic for EMT was assessed for FGFR 1 and 2 by qRT-PCR with specific primers. c-MET was quantified by qRT-PCR and IHC.

Results: Surprisingly, all adrenal tissues lacked E-cadherine expression while N-cadherine was present in both normal and neoplastic adrenal tissues but was significantly lower in malignant vs benign tissues (0.88±0.16 vs 1.64±0.19, P=0.007). SLUG had a uniformly high nuclear expression in all adrenal tissues. FGFR2 mRNA was expressed at lower levels in ACC compared to ACA (3.1±2.1 vs 6.5±2.3 mRNA copies/cell, P=0.0005) whereas FGFR1 (7.5±5.3 vs 4.5±2.9, P=0.09) and FGFR4 (5.1±2.3 vs 2.6±1.3, P=0.002) were higher in ACC. FGFR4 expression was higher in advanced (ENSAT stage 3 and 4) vs localized ACC (6.2±1.6 vs 3.9±2.7, P=0.03). FGF/FGFR pathway analysis confirmed differential FGFR expression and revealed decreased expression of FGF7, FGF17 and mitogen associated protein kinases in tumors compared with NAG. Surprisingly, all adrenal tissues had higher expression of IIIc vs. IIIb isoform expression of both FGFR1 and 2. c-MET expression was significantly higher in ACC compared to ACA and NAG at mRNA but not protein level.

Conclusions: Normal adrenal cortical tissue but also adrenocortical tumors exhibit consistent expression of proteins considered to reflect mesenchymal differentiation. This is probably due to their origin in the intermediate mesoderm. However, significant changes in expression of mesenchymal marker N-cadherine and FGF/FGFR system suggest their relevance in adrenocortical tumorigenesis and progression. Receptor tyrosine kinase FGFR4 may be also a suitable treatment target for advanced ACC.