Distribution of glucagon-like peptide 1 receptor and insulin in phaeochromocytomas

Most phaeochromocytomas produce insulin, and some produce glucagon-like peptide 1 receptor (GLP-1R). In pancreatic β-cells, stimulation of GLP-1R causes insulin release. A few phaeochromocytoma patients experience hypoglycaemic attacks. Therefore, we studied the distribution of GLP-1R-containing and insulin-containing phaeochromocytoma cells and their relation.

In 20 phaeochromocytomas, we performed sequential double staining with anti-insulin and anti-GLP-1R antibodies and, in selected cases, staining with anti-insulin alone. We quantified tumour cells with positive staining and compared their distribution to that of randomly distributed cells using simulations. We obtained GLP-1R transcript data from 182 such tumours from The Cancer Genome Atlas (TCGA) Research Network.

GLP-1R-containing cells were found in six of the 20 tumours, and insulin-containing cells were found in fifteen. Moreover, in the TCGA cohort, almost half of the tumours produce GLP-1R transcripts, and patients with the highest number of transcripts show longer disease-free survival. In the tumours, we found that cells expressing insulin were present in the cytoplasm and GLP-1R in the membrane, with a frequency of 2.59 and 1.34%, respectively. These cells showed clustering, and one tumour showed a large clonal expansion. Interestingly, we found deposits of insulin, which we suggest naming insulin bodies in two tumours. Very few cells contained both proteins.

Most phaeochromocytomas contain tumour cells producing insulin. About half produce GLP-1R. The producing cells show clustering, and clonal expansion occurs. Insulin release might cause hypoglycaemia. Increased GLP-1R levels might induce less aggressive tumours.