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Late-Onset Medullary Thyroid Cancer in a Patient with a Germline RET Codon C634R Mutation.

ABSTRACT: Background: Multiple endocrine neoplasia type 2A (MEN2A) is a rare, hereditary syndrome resulting from a germline mutation in the RET proto-oncogene and characterized primarily by medullary thyroid cancer (MTC), pheochromocytoma (PHEO), and hyperparathyroidism. Types of RET mutation have been associated with age at onset, clinical outcomes of MTC, and the penetrance of other components. Patients classified as 'high-risk' by the American Thyroid Association (ATA), based on the aggressiveness of MTC and the penetrance of other components, are recommended to undergo early prophylactic thyroidectomy at age ≤ 5 years and to be screened for PHEO at age ≥ 11 years. Patients with RET codon C634R mutations have been classified as high-risk. Case presentation: The present study describes a 71-year-old woman newly diagnosed with hereditary MTC related to a RET C634R germline mutation. Her basal serum calcitonin level was high, but there was no evidence of distant metastases. Surgery revealed bilateral MTC with two metastatic lymph nodes. Because microscopic resection was incomplete and extranodal extension was observed, the patient underwent adjuvant external beam radiotherapy. Response to therapy was excellent. Follow-up after 1.5 years showed no evidence of disease or other manifestations of MEN2A. Conclusion: Despite RET C634R carriers being classified as high-risk by the ATA, this patient did not present with either distant MTC or PHEO until her seventies. To our knowledge, only one other patient has shown a similar late identification of a RET C634R mutation, but MTC could not be diagnosed because the patient was lost to follow-up. Further research is required to develop optimal protocols that could allow patients requiring prophylactic thyroidectomy to be differentiated from those who can be monitored closely without early surgery.

SUBMITTER: Walczyk A

PROVIDER: S-EPMC8393343 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Multiple endocrine neoplasia type 2 is an autosomal dominant inherited syndrome caused by activating mutations in the RET proto-oncogene. The RETK666N DNA variant was previously reported in two isolated medullary thyroid carcinoma (MTC) cases, but no family studies are available, and its oncogenic significance remains unknown.The clinical features, genetic data, and family information of eight index MTC patients with a germline RETK666N variant were assessed.Four probands presented with MTC and extensive nodal metastasis, one with biopsy-confirmed distant metastasis. Two additional probands presented with localized disease. However, nodal status was not available. Of the final two probands, one had an incidental 1.5?mm MTC and C-cell hyperplasia uncovered after surgery for papillary thyroid carcinoma, and one had two foci of MTC (largest dimension 2.3?cm) detected after surgery for dysphagia. Genetic screening identified 16 additional family members carrying the K666N variant (aged 5-90 years), 11 of whom have documented evaluation for MTC. Of these, only two were found to have elevated basal serum calcitonin upon screening, and the remaining patients had calcitonin levels within the reference range. One patient who elected to have a thyroidectomy at 70 years of age was confirmed to have MTC. The other subject, 57 years old, elected surveillance. Four prophylactic thyroidectomies were performed, with one case of C-cell hyperplasia at 20 years and three cases that revealed normal pathology at ages 21, 30, and 30 years. None of the K666N DNA variant carriers had evidence of primary hyperparathyroidism or pheochromocytoma.From this case series, the largest such experience to date, it is concluded that the RETK666N variant is likely pathogenic and associated with low penetrance of MTC. However, the findings are insufficient to define its pathogenicity clearly and make firm recommendations for screening and treatment. Given the potential benefit associated with early detection of aberrant C-cell growth, and the noninvasive nature of genetic testing, "at risk" individuals should be screened, and if the K666N variant is identified, they should be managed using a personalized screening approach for detection of MTC.

Project description:Abstract The RET receptor tyrosine kinase proto-oncogene is activated by somatic or germline mutations in a majority of medullary thyroid cancers (MTC). However, treatment of MTC has been challenging due to the lack of effective and tolerable RET-specific therapy, thus testing tumors for the presence of somatic RET mutation has not been warranted. In a first-in-human, phase 1/2 clinical trial (LIBRETTO-001, NCT03157128), selpercatinib (LOXO-292), an investigational, highly selective, potent small molecule RET kinase inhibitor, demonstrated significant and durable anti-tumor activity in patients with advanced RET-mutant MTC or with diverse RET fusion-positive cancers (1). Among the primary analysis set of patients with RET-mutant MTC previously treated with cabozantinib and/or vandetanib (N=55), the investigator-assessed objective response rate (ORR) per RECIST 1.1 was 56% (95% CI 42.3-69.7, n=31/55). Duration of response was not reached with a 10.6-months median follow-up (data cutoff date 17-Jun-2019). Here, we evaluated investigator-assessed ORR per RECIST 1.1 and clinical benefit rate (CBR) in this previously treated patient population by RET alteration and by germline or somatic testing used for enrollment. The ORR remained consistent across subgroups with RET M918T (49%, 95% CI 30.8-66.5, n=16/33), V804M/L gatekeeper mutations (60%, 95% CI 14.7-94.7, n=3/5), extracellular cysteine mutations (43%, 95% CI 9.9-81.6, n=3/7), other mutations (90%, 95% CI 55.5-99.7, n=9/10), and germline (50%, 95% CI 6.8-93.2, n=2/4) or somatic (57%, 95% CI 42.2-70.7, n=29/51) testing. The CBR, defined as the proportion of patients with best overall response of confirmed complete response, confirmed or unconfirmed partial response, or stable disease lasting 16 weeks or more, in this patient set was 87% (95% CI 75.5-94.7, n=48/55). The CBR remained consistent across subgroups with RET M918T (88%, 95% CI 71.8-96.6, n=29/33), V804M/L gatekeeper mutations (80%, 95% CI 28.4-99.5, n=4/5), extracellular cysteine mutations (71%, 95% CI 29.0-96.3, n=5/7), other mutations (100%, 95% CI 69.2-100.0, n=10/10), and germline (75%, 95% CI 19.4-99.4, n=3/4) or somatic (88%, 95% CI 76.1-95.6, n=45/51) testing. The primary technologies used to identify RET alterations were tumor next-generation sequencing (n=43) and polymerase chain reaction (n=9). As previously reported, selpercatinib was well tolerated with an acceptable safety profile (1). These results indicate broad anti-tumor activity for selpercatinib in patients with RET-mutant MTC irrespective of the specific RET mutation, and support implementation of RET mutation testing for patients with advanced MTC, including somatic testing, to identify patients who may benefit from selpercatinib. Reference: (1) Wirth et al., Ann Oncol. 2019 Oct; 30(supplement 5): v933.

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Late-Onset Medullary Thyroid Cancer in a Patient with a Germline RET Codon C634R Mutation.

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