p16INK4a as a proliferation marker unrelated to HPV expression in odontogenic cysts and tumors

INTRODUCTION

p16INK4a is a tumor suppressor protein that retards cell cycle progression from G1 to S phase. Prior studies have evaluated p16INK4a expression in odontogenic keratocyst and ameloblastoma, but data regarding other odontogenic cysts and tumors have been sparse.

METHODS

With IRB approval, cases from the following entities were identified from archives of the UF Oral Pathology Biopsy Service (2005-2015): benign incidental odontogenic rest, dentigerous cyst, lateral periodontal cyst, calcifying odontogenic cyst, glandular odontogenic cyst, odontogenic keratocyst, orthokeratinized odontogenic cyst, adenomatoid odontogenic tumor, calcifying epithelial odontogenic tumor, and ameloblastoma. All cases were submitted for p16INK4a immunohistochemical testing.

RESULTS

Results were scored as follows: nuclear and cytoplasmic staining of <5% cells (score 0), 5%-25% (score 1), 25%-50% (score 2), >50% (score 3). No significant difference in p16INK4a staining was noted between odontogenic cysts and the listed odontogenic tumors (chi-square, P = .540). When comparing lesions with higher recurrence rates (over 25% as reported in the literature) versus lesions with low recurrence rates (under 25%), higher recurrence correlated to significantly higher p16INK4a positivity (chi-square, P = .001). Follow-up testing was performed on 18 cases with "2" or "3" p16INK4a expression scores for high-risk HPV strains through HPV in situ hybridization (ISH) messenger RNA testing with no cases exhibiting a positive result.

CONCLUSION

This study exhibits an association between increased p16INK4a positivity and odontogenic lesions with higher recurrence rates and highlights the role of p16INK4a as a progression marker unrelated to HPV expression in this group of pathologic entities.

Immunohistochemical biomarkers in ameloblastomas

Ameloblastoma is an aggressive odontogenic tumour, which is locally invasive and highly recurrent. Studies show that ameloblastoma is a benign odontogenic neoplasia, being relatively rare and occasionally presenting behaviour of malignant lesions. In addition to these particularities, the histological diagnosis of ameloblastoma can be challenging when the tumour shows high rates of mitosis, absence of nuclear pleomorphism, basilar hyperplasia and neural invasion. In order to help in the diagnosis, prognosis and treatment of this neoplasia, some immunohistochemical markers were shown to be associated with tumoural epithelium. The identification of these markers as well as of their association with clinical signs can be useful to elaborate more efficient treatment strategies and to control this pathology, including improvement of the quality of life of patients affected by this neoplasia. This article aims to review some markers associated with specific molecular pathways, bone remodelling, cell proliferation, apoptosis, cell signalling and tumour suppression.

Immunohistochemistry of Five Molecular Markers for Typing and Management of Ameloblastomas: A Retrospective Analysis of 40 Cases

PURPOSE

The aims of this study are to elucidate if molecular markers can be used to differentiate between the two main types of ameloblastoma (unicystic and solid/multicystic), and to determine whether a biologically 'less-aggressive' subtype exists.

METHODS

A retrospective analysis of 33 solid/multicystic ameloblastomas and six unicystic ameloblastomas was completed using immunohistochemistry for five molecular markers: P16, P53, MMP-9, Survivin, and Ki-67. Tumors were graded as either negative or positive (mild, moderate, strong), and the results were related to both ameloblastoma subtypes and outcomes following treatment.

RESULTS

Unicystic ameloblastomas were more likely to test strongly positive for P53 than solid/multicystic ameloblastomas (p < 0.05), whereas the latter were more likely to be negative for Survivin (p < 0.05). Solid/multicystic and Type 3 unicystic ameloblastomas that were positive for P16, but also negative for MMP-9 and Survivin, were less likely to recur than all other tumors (p < 0.05). The proliferation index of an ameloblastic carcinoma (11 %) was shown to be higher than benign ameloblastomas (4.5 %).

CONCLUSIONS

Immunohistochemistry can be valuable in lesions where histological sub-typing of an ameloblastoma is unclear. A biologically 'less-aggressive' subtype may exist, and hence further research into this area is required.