Association of CK5/6 Expression with Five-Year Mortality Rate in Triple-Negative Breast Cancer
Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited treatment options and variable clinical outcomes. Cytokeratin 5/6 (CK5/6) has been proposed as a potential prognostic marker in TNBC. Objectives: This study aimed to evaluate CK5/6 expression and its association with clinicopathological characteristics and five-year mortality in patients with TNBC. Methods: This retrospective longitudinal study included 50 patients with TNBC who were diagnosed between 2011 and 2016 at Shahid Sadoughi Hospital, Yazd, Iran. CK5/6 expression was assessed by immunohistochemistry using formalin-fixed, paraffin-embedded tissue samples. Clinicopathological variables and five-year mortality were analyzed. Univariate and multivariate logistic regression analyses were performed to identify factors associated with five-year mortality. Results: Among the 50 patients, 45 (90%) exhibited positive CK5/6 expression. Five-year mortality occurred in 10 (20%) patients. CK5/6 expression was significantly associated with five-year mortality (P = 0.01). In univariate analysis, tumor stage (OR = 10.4, 95% CI, 2.40 - 45.08; P < 0.01) and CK5/6 expression (OR = 0.12, 95% CI, 0.01 - 0.87; P = 0.03) were significantly associated with mortality. In multivariate analysis, age (OR = 1.12, 95% CI, 1.01 - 1.23; P = 0.02), tumor stage (OR = 6.36, 95% CI, 1.49 - 27.07; P = 0.01), and CK5/6 expression (OR = 0.04, 95% CI, 0.002 - 0.65; P = 0.02) remained significantly associated with five-year mortality. No significant associations were observed for lymph node involvement, tumor grade, or the CK5/6 staining index. Conclusions: CK5/6 expression was associated with five-year mortality in patients with TNBC and may have prognostic value when evaluated alongside clinicopathological factors. Larger studies are needed to further assess the prognostic role of CK5/6 in TNBC.