Clinical and molecular characterization of parathyroid carcinoma in multiple endocrine neoplasia type 1

Nineteen cases of parathyroid carcinoma in patients with multiple endocrine neoplasia type 1 have been reported in the literature, of which 11 carry an inactivating germline mutation in the MEN1 gene. Somatic genetic abnormalities in these parathyroid carcinomas have never been detected. In this paper, we aimed to describe the clinical and molecular characterization of a parathyroid carcinoma identified in a patient with MEN1. A 60-year-old man was diagnosed with primary hyperparathyroidism during the postoperative period of lung carcinoid surgery. Serum calcium and parathyroid hormone levels were 15.0 mg/dL (8.4-10.2) and 472 pg/mL (12-65), respectively. The patient underwent parathyroid surgery, and histological findings were consistent with parathyroid carcinoma. Analysis of the MEN1 gene by next-generation sequencing (NGS) identified a novel germline heterozygous nonsense pathogenic variant (c.978C>A; p.(Tyr326*)), predicted to encode a truncated protein. Genetic analysis of the parathyroid carcinoma revealed a c.307del, p.(Leu103Cysfs*16) frameshift truncating somatic MEN1 variant in the MEN1 gene, which is consistent with MEN1 tumor-suppressor role, confirming its involvement in parathyroid carcinoma etiology. Genetic analysis of CDC73, GCM2, TP53, RB1, AKT1, MTOR, PIK3CA and CCND1 genes in the parathyroid carcinoma DNA did not detect any somatic mutations. To our knowledge, this is the first report of a PC case presenting both germline (first-hit) and somatic (second-hit) inactivation of the MEN1 gene.