Methods: Paraffin-embedded sections of 14 cases each of UA and SMA were immunohistochemically stained (EnvisionTM Detection System) using three SCP markers: ABCG2, CD44 and Ki-67. The expression patterns of these SCPs were analyzed and their immunoreactivities were semiquantitatively scored in both pre-ameloblast-like (PA-like) basal cells and suprabasal stellate reticulum-like (SR-like) cells in five hotspots/fields at x200 magnification. Level of immunoreactivity was scored as follows: 0 (negative/no staining), + (focal staining in <25% cells), ++ (significant staining in 25-50% cells) and +++ (predominant staining in >50%). Mean scores were obtained for both subsets.
Results: CD44 demonstrated cytoplasmic immunoreactivity in all SR-like cells in both ameloblastoma subsets. However, one case (UA) did not express CD44 in the PA-like cells in two fields while none of the PA-like cells were stained in 2 cases (also UA). ABCG2 immunolocalization was also cytoplasmic. PA-like cells showed least expression of ABCG2 in both UA and SMA. Three UA cases and one SMA case were ABCG2-negative. Ki-67 labelling was predominantly nuclear in the PA-like cells in both UA and SMA. Seven SMA cases Ki-67-negative.
Conclusions: Loss of CD44 expression in PA-like cells in some UA cases may suggest its role in the low aggressiveness of this tumor variant and thus may be useful as a potential marker to predict recurrence rate for various ameloblastoma subsets. ABCG2 overexpression and Ki-67 underexpression in SR-like cells may reflect the existence of SCPMs in these cells which are residing in the quiescent state and may indicate the role of ABCG2 in maintaining tumour cell stemness in the ameloblastoma.