Search for germinal mutations in insulin-producing pancreatic tumors

BACKGROUND: It is known that insulinoma in approximately 5% of cases is associated with multiple endocrine neoplasia type 1 syndrome (MEN1), in which the prognosis and management tactics of patients have been developed in detail. The diagnosis of MEN1 often does not require genetic confirmation, since the syndrome has a typical clinical picture. At the same time, a combination of this tumor with other hereditary syndromes is found in the literature, which are characterized by the presence of malignant neoplasms of various localizations, primary multiple lesions, hormonal and other disorders. Thus, it is relevant to search for the genetic causes that cause the development of insulinoma, in addition to MEN1.

AIM: to evaluate the frequency of detection of genetic causes of the development of insulin-producing tumors of the pancreas, in addition to MEN1; to analyze the phenotypic characteristics of patients with such tumors.

MATERIALS AND METHODS: Based on the analysis of literature for the period up to 2020, a panel has been developed that includes coding regions of 10 genes (MEN1, VHL, TSC1, TSC2, KRAS, YY1, CDKN2A, MLH1, ADCY1, CACNA2D2) involved in the development of insulinoma. In 32 patients diagnosed with insulinoma, verified by pathomorphological examination, with the absence of clinical and/or genetic data indicating MEN1 syndrome, a panel of genes was sequenced with subsequent analysis of the identified genetic variants and phenotypic data obtained from the medical records of patients. In one patient, an additional molecular genetic study of the «Endom» panel was performed, revealing genetic variants of coding regions of 377 genes associated with endocrine diseases.

RESULTS: In 8 patients (25%, 95% CI (11%; 43%)), 9 variants of mutations were identified that were not classified as benign, at that two mutations in the TSC2 gene were detected in one patient. Frequencies of genetic variants: TSC2 — 13%, 95% CI (4%; 29%), MEN1 — 6% (1%; 21%), MLH1 — 3% (0%;16%), CDKN2A/P16INK4A — 3% (0%;16%). When comparing patients with the identified mutation, with the exception of benign (n=8), and patients without mutation or with a benign mutation (n=24), there were no differences in the Grade (degree of differentiation), Ki67 proliferation index, frequency of concomitant tumors, burdened history, multiple pancreatic lesions or recurrence of insulinoma, however, patients with germinal mutation were found at the level of statistical trend to be younger at the manifestation of insulinoma and to have bigger tumors. In a patient who underwent an additional molecular genetic study using the new «Endome» panel, previously undescribed gene variants (APC and KIF1B) associated with various sporadic tumors, including endocrine ones, were identified.

CONCLUSION: A panel of 10 genes has been developed, mutations of which are associated with insulinoma. A relatively high incidence of genetically determined insulinoma was determined (25% of cases), in half of cases — against the background of tuberous sclerosis. We consider it relevant to evaluate the effectiveness of genetic testing for patients with insulinoma. We believe that, first of all, patients with a high risk of hereditary pathology should be examined: with the manifestation of the disease at a young age and with a large tumor. The identification of a genetic mutation will make it possible to determine the prognosis of the disease, optimize the monitoring algorithm in order to timely identify concomitant diseases-components of the hereditary syndrome, and conduct genetic counseling of the family.

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