Pediatric chordoma associated with tuberous sclerosis complex: A rare case report with a thorough analysis of potential therapeutic molecular targets.

Chordoma associated with tuberous sclerosis complex (TSC) is an extremely rare tumor that was described only in 13 cases since 1975. Сhordoma itself is a malignant slow-growing bone tumor thought to arise from vestigial or ectopic notochordal tissue. Chordoma associated with TSC differs from chordoma in the general pediatric population in the median age, where the diagnosis of TSC-associated chordoma is 6.2 months, whereas for chordoma in the general pediatric population it is set to 12 years. The majority of TSC-associated chordomas are localized in skull-based and sacrum regions, and rare in the spine. Chordomas are genetically heterogeneous tumors characterized by chromosomal instability (CIN), and alterations involving PI3K-AKT signaling pathway genes and chromatin remodeling genes. Here we present the 14th case of chordoma associated with TSC in a 1-year-old pediatric patient. Alongside biallelic inactivation of the TSC1 gene, molecular genetic analysis revealed CIN and involvement of epigenetic regulation genes. In addition, we found the engagement of CBX7 and apolipoprotein B editing complex (APOBEC3) genes that were not yet seen in chordomas before. Amplification of CBX7 may epigenetically silence the CDKN2A gene, whereas amplification of APOBEC3 genes can explain the frequent occurrence of CIN in chordomas. We also found that KRAS gene is located in the region with gain status, which may suggest the ineffectiveness of potential EGFR monotherapy. Thus, molecular genetic analysis carried out in this study broadens the horizons of possible approaches for targeted therapies with potential applications for personalized medicine.