Whole‑exome sequencing unveils novel potential gene mutations involved in primary renal small cell carcinoma

Primary renal small cell carcinoma (PRSCC) is a rare, poorly differentiated neuroendocrine carcinoma, and its clinicopathological features and the gene mutation spectrum associated with its pathogenesis remain to be elucidated. The present study aimed to characterize the genetic mutation spectrum associated with the pathogenesis of PRSCC, identify novel driver and predisposing genes for the disease, reveal its histopathological features associated with genetic mutations and systematically summarize the clinicopathologic characteristics and prognostic factors of PRSCC patients to provide a theoretical basis for molecularly targeted therapy and prognostic assessment of PRSCC. Whole‑exome sequencing (WES) was performed on PRSCC samples to characterize the spectrum of genetic mutations and the results were validated using Sanger sequencing. Immunohistochemistry (IHC) was performed to reveal the histopathological features associated with these mutations. Furthermore, based on the published literature, a population‑based study was conducted by searching PubMed and EMBASE databases to systematically summarize the clinicopathologic characteristics and prognostic factors of patients with PRSCC. WES identified 113 somatic single‑nucleotide variants, 26 somatic insertions and deletions and mutations in 8 predisposing genes (DST, OR10H3, PTK2B, APOBR, ZNF606, CCN4, ADCK1, and MYH2) and 10 driver genes (KRTAP10‑9, HYDIN, ZNF665, KRTAP10‑2, GPAM, MUC12, KRT9, CCDC168, DUSP27 and MDC1). Sanger sequencing of germline DNA identified a germline A/G variant in the HYDIN sequence, first reported in PRSCC. Furthermore, IHC analysis indicated that PRSCC was positive for CD56, Syn, insulinoma associated protein 1, CgA and neuron specific enolase. In the population‑based study, the majority of patients with PRSCC were elderly (57.92±15.75 years), with a pathological tumor (T) 3/4 stage (68.3%) and presented with lymph node involvement (51.7%) and distant metastasis (51.7%). T stage was an independent prognostic factor for overall survival in patients with PRSCC (P=0.004). Driver mutations in the HYDIN gene may be a key factor in the pathogenesis of PRSCC. HYDIN may serve as a prognostic marker and a target for immunotherapy in the management of PRSCC. However, due to the extreme rarity of PRSCC, the WES analysis in the present study was based solely on individual cases. To ensure the reliability and generalizability of genetic alterations detected by WES, additional PRSCC samples, along with cell and animal experiments, are warranted to confirm the role of these genetic variants (particularly HYDIN) in PRSCC pathogenesis. The functional role of HYDIN mutations in PRSCC pathogenesis requires further validation in future research.