Association of a CD44s-v5-v6 Null Phenotype with Advanced Stage Cholangiocarcinoma: A Preliminary Study

Background/Objectives: Cholangiocarcinoma (CCA) is an aggressive malignancy with a poor prognosis, creating an urgent need for novel biomarkers to improve risk stratification. The prognostic significance of the transmembrane glycoprotein CD44 and its isoforms (CD44s, v5, v6) in CCA remains controversial. This preliminary study aimed to investigate whether the combined loss of these isoforms could serve as a distinct prognostic indicator. Methods: We evaluated the expression of CD44s, CD44v5, and CD44v6 via immunohistochemistry on a retrospective cohort of 61 paraffin-embedded CCA patient tissue blocks from Ramathibodi Hospital, Bangkok, Thailand. Expression levels were correlated with clinicopathological parameters. Survival analyses, including Kaplan-Meier and Cox proportional hazards models, were used to determine the prognostic value of individual isoforms and the complete absence of all three. Results: Expression of CD44s, CD44v5, and CD44v6 was found in 52.5%, 47.5%, and 82.0% of tumors, respectively. In univariate and multivariate analyses, the expression of any single isoform was not a significant predictor of overall survival. However, a subgroup of 8 patients (13.1%) was identified whose tumors were negative for all three isoforms, a phenotype we termed "CD44s-v5-v6 Null". This status was significantly associated with advanced TNM stages (p = 0.022). Patients with these Null tumors also showed a clinically relevant, though not statistically significant, trend towards poorer survival (median 7.0 vs. 12.0 months, p = 0.336). Conclusions: Individual CD44 isoforms did not serve as reliable independent prognostic markers in this cohort. Instead, the complete loss of the CD44 expression program characterizes a potential "CD44s-v5-v6 Null" phenotype associated with advanced-stage disease.