Aberrant membranous localization of cleaved caspase-3 in anaplastic thyroid carcinoma: Implications for cell proliferation and stemness.

Anaplastic thyroid carcinoma (ATC) is among the most aggressive malignancies. Patients with ATC have poor prognoses and require novel therapies. Cleaved caspase-3 (CC3) has pivotal functions in apoptosis and is usually present in the nuclei and cytoplasm of apoptotic cells. We investigated the aberrant membranous localization of CC3 in thyroid carcinoma (TC) and its diagnostic and clinicobiological significance. We examined the expression of nuclear/cytoplasmic CC3 (n/cCC3) and membranous CC3 (mCC3) in 80 primary and one metastatic TC samples. Receiver operating characteristic curve analysis was used to evaluate their diagnostic efficacy for ATC. Multivariate logistic regression analysis was used to identify risk factors for large tumor size. The n/cCC3 and mCC3 indices were significantly greater in ATC than in other types of TC (P < 0.001). Moreover, the area under the curve and sensitivity of mCC3 were greater than those of n/cCC3 for identifying ATC (0.961 versus 0.948 and 95.0% versus 90.0%). A preabsorption test confirmed the specificity of CC3 immunostaining. However, Western blotting indicated that the anti-CC3 antibody crossreacted with an unknown protein with epitopes common to those of CC3. Significant correlations were detected between Ki-67 and n/cCC3 (ρ = 0.536, P < 0.001) and mCC3 (ρ = 0.680, P < 0.001). Multivariate analysis revealed that mCC3 was an independent risk factor for large tumor size. Double immunofluorescence staining demonstrated that mCC3-expressing ATC cells were Ki-67-negative but occasionally SOX2-positive. Our results suggest that mCC3 may have diagnostic value for ATC and that mCC3-expressing ATC cells may be involved in cell proliferation and stemness.