it is a relatively rare odontogenic lesion which exists either as a cystic or a solid variant and is characterised by varied clinical , radiographical and biological features . the central ccot appears as a unilocular or multilocular destructive radiolucent lesion containing irregular calcifications . various terminologies used for ccot include calcifying odontogenic cyst , gorlin cyst , calcifying ghost cell odontogenic tumour and epithelial odontogenic ghost cell tumour , keratinizing calcifying odontogenic tumour . in 2005 , the world health organization classification of head and neck tumors reclassified ccot as an odontogenic tumor and gave it the name of  calcifying cystic odontogenic tumor  . is a developmental cyst of odontogenic origin and constitutes about 0.37% to 2% of all odontogenic tumours . ccot are cysts of primordial origin and not associated with crown of any impacted tooth . ccot may occur as a central lesion or as a peripheral lesion ( although rare ) . a comprehensive review of the available literature relating to malignant transformation of ccot was undertaken using medline , pubmed , google scholar and scopus in all languages . we used the following keywords for searching : calcifying cystic odontogenic tumour , malignancy and ghost cell odontogencic carcinoma from 20032013 . we also used the  related articles  feature of pubmed to identify further references of interest within the primary search . these articles were obtained , and from their references lists , pertinent secondary references were also identified and acquired . ghost cell odontogenic carcinoma ( gcoc ) is a rare tumour which is a malignant counterpart of ccot . ghost cell odontogenic carcinoma may arise as a denovo tumour or from previously existing ccot . one third cases of ghost cell odontogenic carcinoma are reported to be derived from a preexisting ccot and malignant transformation may take several years . however some of the ghost cell carcinoma may develop without history of ccot [ 1214 ] . recurrent ccot and gcoc are more common in the maxilla [ 8 , 15 ] . painful swelling with local paraesthesia is the most common symptom of ghost cell odontogenic carcinoma . some authors reported of infiltrative growth , root resorption and tooth displacements in cases of gcoc [ 16 , 17 ] . ct scan demonstrated bone expansion and bone destruction with irregularly shaped calcified inside the lesion . magnetic resonance images showed a mass with high signal intensity . li et al . reported an ameloblastoma - like epithelia with prominent features being presence of lots of ghost cells , dysplastic uncalcified dentin or osteodentin . increased nuclear / cytoplasmic ratio with 12 nucleoloi and atypical mitotic figures were also reported . according to motsugi et al . , tumour cells densely proliferates the epithelial component and the nucleus of tumour cells were enlarged and variable in size . immunohistochemical analysis of gcoc by motossugi et al . revealed that 70% of tumour cells were reactive for p53 and ki-67 index was 4% to28% . expression of ki-67 , mmp-9 and timp-1 was stronger in gcoc when compared to ccot . mmp-9 in stroma is associated with invasive ability of ccot and gcoc and ki-67 is associated with increased cellular proliferation . according to gomes et al . , there is a variable expression of syndecan-1 in stellate reticulum , stromal cells and basal cells of ccot and gcoc and might be associated with the biology of these tumors . a total of 8 cases have been reported in the literature from 2003 - 2013 where ghost cell odontogenic carcinoma has probably developed from ccot . these cases are enlisted in table 1 , [ 8 , 13 , 14 , 1618 , 21 , 22 ] . of the 29 patients diagnosed , 5 died of local recurrence and metastasis to brain and lung has been reported . the most commonly employed treatment was surgery with wide excision . in some cases radiotherapy and after reviewing the literature we conclude that recurrent and long standing case of ccot can undergo malignant transformation . gcoc , the malignant form of ccot can metastasize and can even lead to deaths . so it is mandatory to follow up the patients with ccot for possible eventual development of malignant counterparts .
calcifying cystic odontogenic tumour ( ccot ) has been classified as an odontogenic tumour . 
 ghost cell odontogenic carcinoma ( gcoc ) is the malignant counterpart of ccot . 
 this paper aims to review the literature regarding malignant transformation of ccot.a literature search was done via the national library of medicine pubmed interface , searching for articles relating to malignant transformation of ccot . from these articles , 
 references were obtained , and from their references lists , pertinent secondary references were also identified and acquired.after reviewing the literature , we found 26 cases of gcoc which developed from ccot . 
 malignant transformation of ccot was seen more commonly in the maxilla . 
 histologically , changes such as increased nuclear / cytoplasmic ratio , atypical mitotic figures have been reported after malignant transformation . 
 immunohistochemical analysis has shown an increased expression of ki-67 and p53 in tumour cells.malignant transformation of ccot , although rare , mostly takes place in recurrent and long standing cases .