ABSTRACT
Aim:
The present study was conducted for assessing variability in calretinin expression among odontogenic cysts as well as tumor cases.
Materials and Methods:
Fifteen cases were included in the present research consisting of cases like – dentigerous cyst, odontogenic keratocyst, apical radicular cyst along with tumors like ameloblastoma, ameloblastic carcinoma, adenomatoid odontogenic tumor. Calretinin antibody was used for immunohistochemical staining. The amount of expression of this calretinin was statistically analyzed with the help of Chi-square test where P < 0.05 was considered noteworthy statistically.
Results:
Most cases of ameloblastomas were highly positive for calretinin expression as compared to other cysts and tumors. Therefore, the correlation of this variation of expression of calretinin was statistically noteworthy (P = 0.00).
Conclusion:
In this study, we concluded that for ameloblastomas, calretinin can be a specific marker immunohistochemically and can help in identifying the amount of aggressive spread of various odontogenic tumors.
KEYWORDS: Calretinin, immunohistochemistry, odontogenic cyst and tumors
INTRODUCTION
Tumors and cysts of odontogenic nature have three different origins – ectomesenchymal, mesenchymal, and epithelial.[1] It is imperative to diagnose these lesions with the help of clinical, radiological as well as histopathology features. Certain benign cysts and tumors of odontogenic origin have a hostile course, which can mimic malignant tumors as well. The overlapping histological appearances make differential diagnosis between these lesions difficult. This makes the appropriate diagnostic judgment even more crucial for pathologists as it will affect treatment modalities or, if not performed in a proper way, can lead to incompetent treatment. One of the most important ions that regulate cell division, metabolism, cell growth, memory storage etc., is calcium ion. The increased level of calcium ions has been related to an increase in the aggressiveness of the tumor as a whole. Intracellular responses are regulated with the help of many calcium-binding proteins like EF (elongation factor)-hand protein.[2] Being a calcium-binding protein, calretinin has a molecular weight of 29 kDa, which is one of the major molecules being expressed among various stages of odontogenesis. This is also evident in many studies where the calretinin expression is prominent in odontogenic cysts and tumors, especially ameloblastoma.[3,4,5,6,7] However, many other studies do not agree that calretinin can be a specific marker for identifying ameloblastomas.[8,9] Diagnosis in cases of odontogenic cysts and tumors can be challenging due to heterogeneity in terms of histopathology in lesions of the maxilla as well as mandible, as these are the common sites of tooth formation as well. Development of these types of lesions has also been associated with mutated calretinin gene, especially at the level of messenger ribonucleic acid (mRNA) in the case of ameloblastoma tumor cells, which differ from normal ameloblast cells, leading to the conclusion that the former suffers from defective functional maturation.[9] Calcium levels’ defective balance also has a role in tumor formation, where these ions can cause genetic damage.[10] The successional dental laminae can initiate the development of odontogenic tumors where many cellular factors can trigger the epithelial rests, which in turn leads to the biological aggressiveness of the odontogenic tumors. Calretinin also has a role in the pathogenesis of ameloblastoma since it helps in the changeover of the rest of dental lamina into tumor cells and, in turn, leads to the invasiveness of most of the odontogenic tumors.[11]
MATERIALS AND METHODS
In our research, we took a total of 68 odontogenic cysts and tumor tissue blocks embedded in paraffin from the archives of the oral pathology department. Cases were mostly of dentigerous cysts, radicular cysts, ameloblastoma, odontogenic keratocyst, other odontogenic tumors like adenomatoid odontogenic tumor and ameloblastic carcinoma. Immunohistochemical (IHC) staining of these unstained tissue slides was performed with calretinin. The colon tissue section was used as a positive control. The variation in staining of calretinin was observed through a 100x light microscope using dibutyl phthalate xylene (DPX) as a mounting media where the scoring system varying from 0–3 (no staining–intense staining) based on the amount of calretinin positivity. The ratio was then calculated, where the number of calls stained was compared to the total number of cells, and the result was calculated in percentage format. Statistical measures like the Chi-square test were also used to analyze the information obtained where P < 0.05 was significant.
RESULTS
We observed that in our study samples, all ameloblastomas were positive for calretinin expression, which was not observed in other cysts and tumors. In the case of unicystic ameloblastomas, around five cases were moderately positive for calretinin expression. The pattern of immuno histo chemistry (IHC) expression was mostly seen in cells that resemble stellate reticulum. As far as plexiform ameloblastoma cases were concerned, four cases were intensely positive for calretinin, which was also similar to cases of the follicular variant as well. Mostly, odontogenic cysts had little or no expression of calretinin expression. Positivity was seen in mast cells as well as adipocytes. It was statistically noteworthy of calretinin expression (P = 0.00). [Table 1]
Table 1.
Variability of calretinin expression in odontogenic cysts and tumors
| Odontogenic lesion | Number of cases positive for calretinin | Number of cases negative for calretinin | Total positivity seen | Test value | P |
|---|---|---|---|---|---|
| Ameloblastoma | 15 | 0 | 15 | 68.000 | 0.000 |
| Adenomatoid odontogenic tumor | 0 | 5 | 5 | ||
| Ameloblastic carcinoma | 0 | 3 | 3 | ||
| Dentigerous cyst | 0 | 15 | 15 | ||
| Odontogenic keratocyst | 0 | 15 | 15 | ||
| Radicular cyst | 0 | 15 | 15 |
DISCUSSION
Calretinin, a protein, is prevalent in humans and has widespread tissue distribution as well. Apart from humans, calretinin was also evident in the case of periodontal ligament cells of rats. It has been studied in ovarian and cardiac tumors in humans.[12,13] This protein, which helps in calcium ions binding, was first demonstrated in molar tooth germs, where the expression was predominant in all layers made of the odontogenic epithelium at various stages of the tooth formation cycle. However, in contrast to all the layers, inner enamel epithelium and secretory type of ameloblasts had lesser expression of calretinin. But, it cannot be denied that calretinin has a role to play in amelogenesis.[14] Most common odontogenic cysts like odontogenic keratocyst (OKC), apical periodontal cysts, and dentigerous cysts have been shown to have histological mimics, which makes their identification a bit cumbersome in few cases, especially those dealing with their inflammatory variants.[15] In our study, the IHC positivity of calretinin was analyzed, which helps in diagnosing a lesion in cases where the usual histopathological features are not clearly delineated. Ameloblastomas were intensely positive, with all cases of unicystic ameloblastoma being prominently stained with calretinin, which was also the result in a study conducted by various other researchers.[13] In another research by Altini et al.,[7] 81% of cases of unicystic ameloblastoma, whereas the cells that had undergone squamous metaplasia, were negative for calretinin. 50% of diffuse positivity was evident in research conducted by Anandani et al.,[13] which they thought was due to variability of differentiation of odontogenic epithelium. Hence, most scholars felt that calretinin positivity was not fixed for a particular tumor or a cyst. In our research, unicystic ameloblastoma cases were intensely positive for the calretinin expression, but the concentration was more in the stellate reticulum-like cells. Even the areas having metaplasia of cells had some positivity apart from the basal cells of the ameloblastic epithelium.[8]
CONCLUSION
It was concluded in our research that, as compared to other cysts and tumors, ameloblastomas and odontogenic keratocysts were very much positive for calretinin IHC expression. This finding can help establish calretinin as a distinguishing marker for these lesions and also help pathologists in identifying the invasiveness of these kinds of lesions.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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