Background: Mutations in genes encoding one of the subunits of succinate dehydrogenase (SDH) are involved in pheochromocytoma (PHEO) and paraganglioma (PGL) development. Over the last few years, such mutations have also been associated with non-chromaffin tumors. However, immunohistochemistry (IHC) on the tumor tissue and a study on the loss of heterozygosity (LOH) aimed at demonstrating the pathogenic role of SDHx genes have only been employed in a few cases. Case report: We describe the case of a 19-year-old Caucasian man with a germline SDHB mutation, who presented with acne vulgaris resistant to medical treatment. His follow-up for chromaffin tumors was negative, while hormonal tests revealed suppressed gonadotropins with testosterone in the upper range of normality and elevated β-human chorionic gonadotropin (β-hCG). At the whole-body enhanced CT scan, a mediastinal lesion suggestive of a germ cell tumor (GCT) was detected. 18FDG-PET (fluorodeoxyglucose-positron emission tomography) imaging showed low glucose metabolism at the mediastinal site. Surgical removal of the mass was uneventful. Pathology confirmed the diagnosis of GCT consisting of cystic teratoma (95%) and seminoma (5%). IHC for SDHB showed normal protein expression, and genetic analysis of the tumor tissue revealed the absence of SDHB LOH. Normalization of the hormonal tests and acne attenuation were achieved after surgery. Conclusion: We report an incidental association of a germinal SDHB mutation and mediastinal GCT in a young Caucasian man. Our paper highlights the importance of IHC and genetic analysis in confirming the etiologic role of SDHx genes in nonchromaffin tumors, thus excluding incidental associations.

Background: Pheochromocytoma (Pheo) and paraganglioma (PGL) are rare tumors, mostly resulting from pathogenic variants of predisposing genes, with a genetic contribution that now stands at around 70%. Germline variants account for approximately 40%, while the remaining 30% is attributable to somatic variants. Objective: This study aimed to describe a new PHD2 (EGLN1) variant in a patient affected by metastatic Pheo and chronic myeloid leukemia (CML) without polycythemia and to emphasize the need to adopt a comprehensive next-generation sequencing (NGS) panel. Methods: Genetic analysis was carried out by NGS. This analysis was initially performed using a panel of genes known for tumor predisposition (EGLN1, EPAS1, FH, KIF1Bβ, MAX, NF1, RET, SDHA, SDHAF2, SDHB, SDHC, SDHD, TMEM127, and VHL), followed initially by SNP-CGH array, to exclude the presence of the pathogenic Copy Number Variants (CNVs) and the loss of heterozygosity (LOH) and subsequently by whole exome sequencing (WES) comparative sequence analysis of the DNA extracted from tumor fragments and peripheral blood. Results: We found a novel germline PHD2 (EGLN1) gene variant, c.153G>A, p.W51*, in a patient affected by metastatic Pheo and chronic myeloid leukemia (CML) in the absence of polycythemia. Conclusions: According to the latest guidelines, it is mandatory to perform genetic analysis in all Pheo/PGL cases regardless of phenotype. In patients with metastatic disease and no evidence of polycythemia, we propose testing for PHD2 (EGLN1) gene variants. A possible correlation between PHD2 (EGLN1) pathogenic variants and CML clinical course should be considered.