8657 Thymic Neoplasia in a Pediatric Patient With LI-Fraumeni Syndrome: A Case Report

Abstract Disclosure: M.A. Souza: None. W.M. Lins: None. D. di Matteo: None. J.L. Marcayata: None. A. Kuhn: None. H. Charcar: None. F. Ledesma: None. M.Q. Almeida: None. F. Jatene: None. B.B. Mendonca: None. M.C. Fragoso: None. Introduction: Li-Fraumeni Syndrome (LFS) is a rare autosomal dominant hereditary cancer predisposition syndrome primarily caused by pathogenic variants in the TP53 tumor suppressor gene. The individuals affected are typically young, with a cancer risk of approximately 90% in lifetime. Parents choosing to test their young children face the dilemma of when to disclose their own or the child's status and when to initiate cancer screening if LFS is detected. This process presents psychosocial challenges for both parents and affected children. Both providers and patients question whether the surveillance benefits outweigh the psychological burden of knowing LFS status and screening-related concerns, creating ambivalence toward genetic testing decisions.Case Report: We describe a 6-year-old male with Li-Fraumeni syndrome carrier of the germline pathogenic variant TP53 c.818G>A (p.R273H) in heterozygous (exon 8).In the family history, there are three relatives with advanced tumor cases, with the grandmother already deceased, the mother undergoing chemotherapy treatment, and the cousin being cancer-free for 10 years.The patient in question had no gestational complications. No consanguinity between parents. No signs or symptoms of hormonal hyperfunction. As proposed in the literature, Li-Fraumeni Syndrome patients should undergo frequent screening for early tumor detection, the patient began screening according to the Toronto protocol in 2018, at the age of 1 year and 7 months, through cranial and thoracic MRI, abdominal ultrasound, and annual hormonal assays. In the thoracic MRI conducted in February 2023, an enlarged and heterogeneously signaling thymus was identified, with a nodular formation (absent in previous exams), measuring about 2.5 cm. Facing suspicion of a thymoma, thymic carcinoma, or lymphoma, a biopsy guided by tomography in March 2023 was done. Histological examination was compatible with primary thymic neoplasia. During follow-up, a significant growth of the mass to 9 cm was observed. The patient underwent surgical treatment in August 2023 with resection of the mediastinal mass, and the anatomopathological examination revealed undifferentiated thymic carcinoma, followed in conjunction with the pediatric oncology team. The dilemma is about the adjuvant radiotherapy since the possibility to acquire a new tumor radio-induced such as sarcoma. We proposed to follow with MRI imaging each 3 months and if minimal signal of recurrence he will underwent radiotherapy. Conclusion: In addition to the intrinsic rarity of Li-Fraumeni Syndrome, this case draws attention to the possibility of a thymic tumor, an extremely rare neoplasm in syndrome carriers. In the literature, only scattered case reports show this association. Furthermore, this case reinforces the importance of systematic screening for investigating possible neoplasms in this susceptible population. Presentation: 6/1/2024