O-11 A rare cause of thyroid cancer - Li Fraumeni 2 syndrome
Authors: Talaibekova Sezim , Saygili Emre Sedar , Karakiliç Ersen 
Published: January 2024

Abstract

Introduction
Thyroid cancer often originates from follicular cells, and papillary thyroid cancer (PTC) is the most common type. There is a familial predisposition in some cases of thyroid cancer. However, a minority of cases have thyroid cancer syndrome (e.g., familial polyposis, MEN 2, or Cowden syndrome). Many known genetic susceptibility genes are RET/PTC, BRAF, RAS, TERT, and TP53. We want to present a case of Li Fraumeni type 2 syndrome as a rare cause of thyroid cancer.

Clinical Case
A 69-year-old female patient with a history of PTC is admitted to the endocrinology department for follow-up. In 1976, this patient had a thyroid lobectomy, but the pathology result is unknown, and she takes 75 mcg of levothyroxine daily. In 1999, she was diagnosed with rectal cancer. The patient had a completion thyroidectomy in 2002, and the pathology was compatible with PTC. In 2014, she was diagnosed with right breast noninvasive ductal cancer. Cases of cancer were also quite common in her family history. The results of laboratory tests revealed normal TSH levels with negative thyroglobulin and anti-thyroglobulin levels. Neck ultrasonography showed no rest gland and pathological LAP. We requested genetic analysis (55 genes) for familial cancer syndromes. As a result of the analysis, 2 genes were found to be heterozygous. The c.599T&gt;c heterozygous variant in the CHEK 2 gene was found (Figure 1). It was evaluated as pathogenic in the database review. Another heterozygous mutation in the BRIP1 gene, which was evaluated as a VUS also detected.

Conclusion
The CHEK 2 gene is a DNA-repairing protein kinase at position 22.q12.1. It is responsible for TP53 stabilization, genome maintenance, and apoptosis. CHEK2 phosphorylates p53 in response to DNA damage, leading to cell cycle arrest and stabilization (Figure 2). The mutation(CHEK 2 c.599T&gt;c) we detected in this case has been considered possibly pathogenic in the academic databases. There are reported CHEK 2 c.599T&gt;c cases on the CLINVAR site; the first report is from 2013. Classic Li-Fraumeni syndrome is a rare autosomal dominant syndrome caused by TP53 gene mutation. The chromosome location on classical Li fraumeni is 17p13.1. Li-Fraumeni type 2 develops due to the CHEK 2 gene mutation on chromosome 22q12.1. The results of a mutation of the CHEK2 gene are breast cancer, prostate cancer, PTC, colon cancer, kidney cancer, adrenocortical cancer, lung cancer, and rare cases of myelodysplastic syndromes. There are no data on thyroid-specific mortality in carriers of the CHEK2 mutations, and it is not yet known whether thyroid cancer in this population is more aggressive or has a better outcome.The familial syndromes should also be considered if PTC is detected in breast, colon, and prostate cancer patients. Studies on Li-Fraumeni type 2 syndrome are scarce, and considering the prevalence in European countries, further investigations of this syndrome and screening in patients with multiple cancers in the family should be warranted.Figure 1.Genetic sequencing image of the case