BCL-2 and Ki-67 expression in Odontogenic Keratocysts

Introduction

Odontogenic keratocyst/keratocystic odontogenic tumor (OKC/KCOT) is a cystic odontogenic neoplasm that harbors PTCH1 gene mutation in 93% of the cases. BCL-2 is an anti-apoptotic gene that functions through the regulation of Ca 2 concentration, maintenance of mitochondrial integrity and promoting cell survival during the G0 of cell cycle when growth factors are depleted. It is expressed in some benign neoplasms such as spindle cell lipoma and solitary fibrous tumor.

Aim

We aim to investigate the expression of BCL-2 and Ki-67 in OKC/KCOT compared to other odontogenic cysts and tumors.

Methods

26 cases of sporadic OKC/KCOT and 24 controls, including 15 dentigerous cysts, nine other odontogenic cysts and three cases of unicystic ameloblastoma were stained for BCL-2 and Ki-67.

Results

The epithelium exhibited dysmaturation in >1/3 of the epithelium in 15 (57.7%) of the cases. All cases (100%) were positive for BCL-2 involving basal cell cytoplasm with 15 cases (57.7%) involving up to one third of the epithelium, and 3 (11.5%) involving more than one-third of the epithelium. Expression of BCL-2 was completely lost in areas where the epithelium was inflamed. Ki-67 showed >30% expression in 19 cases at least focally while the rest showed 5-30% positivity. Ki-67 expression was significantly higher in cases that exhibited dysmaturation in >1/3 of the epithelium (p= 0.032). None of the cyst controls were positive for BCL-2 expression. All three cases of unicystic ameloblastoma were diffusely positive for BCL-2.

Conclusion

BCL-2 is a sensitive marker for OKC/KCOT staining the basal cell cytoplasm in 100% of cases. It is useful in identifying cases with histologic features suggestive of but not definitive for OKC/KCOT especially in small specimens, as well as for excluding this diagnosis in cysts that exhibit focal parakeratosis without other features of OKC/KCOT.