BBS5 as a robust prognostic biomarker in esophageal squamous cell carcinoma: validation in two independent cohorts.

Esophageal squamous cell carcinoma (ESCC) remains a highly lethal malignancy, and reliable biomarkers for predicting metastasis and prognosis are urgently needed. Through comprehensive transcriptomic profiling, we identified Bardet-Biedl syndrome 5 (BBS5) as a potential biomarker of clinical significance. Transcriptome analysis was performed on surgical specimens from eight ESCC patients with distant metastatic recurrence (discovery cohort, n = 8). BBS5 mRNA expression was quantified by Reverse Transcription Quantitative PCR (RT-qPCR) across 18 ESCC cell lines, and siRNA-mediated knockdown was conducted in two independent high-expressing lines (KYSE1260 and KYSE590) to assess proliferation in both cell lines and migration and invasion in KYSE1260. In 266 patients who underwent curative esophagectomy, BBS5 mRNA levels were measured by RT-qPCR and correlated with clinicopathological features and survival outcomes. Among these, 98 cases additionally underwent immunohistochemical (IHC) assessment of BBS5 protein expression. A second (independent) cohort of 175 ESCC patients was further analyzed using tissue microarray (TMA)-based IHC to validate prognostic relevance. BBS5 knockdown significantly inhibited proliferation of the BBS5-high ESCC cell lines KYSE1260 and KYSE590, markedly suppressed invasion in KYSE1260 and reduced the migratory capacity of KYSE1260. Tumors exhibited significantly higher BBS5 mRNA expression than adjacent normal tissues. High BBS5 expression was associated with significantly shorter overall survival (P = 0.025), and multivariate analysis identified BBS5 expression as an independent predictor of overall and disease-free survival. IHC analysis confirmed the association between high BBS5 expression and poor prognosis, which was further validated in the second (independent) TMA cohort, in which high BBS5 protein expression independently predicted both overall and disease-free survival. BBS5 promotes ESCC cell proliferation, migration and invasion and serves as a robust prognostic indicator in two independent patient cohorts, highlighting its potential utility as a clinically relevant biomarker.