Evaluation of CK8/18 and CK19 Expression as Adjunct Immunohistochemical Markers in Non-Keratinizing Nasopharyngeal Carcinoma.

Background: Nasopharyngeal carcinoma (NPC), particularly the non-keratinizing subtype (NK-NPC), is prevalent in Southeast Asia and often presents diagnostic challenges due to overlapping histological features with benign nasopharyngeal lesions. While Epstein-Barr virus (EBV) serology supports diagnosis in many cases, its limitations in sensitivity and specificity necessitate additional tissue-based markers. Objective: To assess the immunohistochemical expression of cytokeratins CK8/18 and CK19 in NPC compared to benign nasal tissue and evaluate their potential as adjunct immunohistochemical markers. Methods: This retrospective study evaluated the immunohistochemical expression of cytokeratins CK8/18 and CK19 in 24 NK-NPC and 22 benign nasopharyngeal tissue samples collected between April 2021 and April 2024 at Hospital Canselor Tuanku Muhriz, Kuala Lumpur, Malaysia. Staining intensity and distribution were scored semi-quantitatively, and statistical analysis was performed using SPSS v29.0 (p < 0.05). Results: CK19 was expressed in all NK-NPC cases, with strong positivity in 79.2%, while CK8/18 was positive in 92%, primarily with weak to moderate staining. Only one benign case (inverted papilloma) showed focal positivity. The differences in expression between malignant and benign tissues were statistically significant (p < 0.001). Sub-analysis of EBER-positive cases (n = 15) confirmed consistently strong CK19 expression. Conclusions: Based on this small retrospective cohort, CK8/18 and particularly CK19 demonstrate expression patterns that may support their use as adjunct immunohistochemical markers in the histopathological assessment of NK-NPC, especially in morphologically ambiguous cases. Further validation in larger studies is needed before these markers can be considered for routine diagnostic application.