lipomas represent uncommon neoplasms of the oral cavity ; only 1% to 5% of cases occur at this site . based on their histopathological features of conspicuous multiple components , lipomas can be divided into some subclasses [ 2 , 3 ] , and the most common is the fibrolipoma [ 1 , 3 , 4 ] . cases reporting on lipoma with osteo / chondroid differentiaion were only 16 cases as a result of retrieving literature from 1960 to 2008 . further , other names of this subclassification exist in literature ; osteo / chondrolipoma , ossifying / osseous lipoma , lipoma with chondro / osseous metaplasia , and lipoma with cartilaginous / osseous change . the obscure etiology of osseous / chondroid differentiaion led to confusion of the name . to clarify the etiology of osseous / chondroid differentiaion in lipoma , the authors report additional 2 cases of oral lipoma / fibrolipoma with osseous and/or chondroid differentiation and describe the clinical , histopathological , and immunohistological features of these . review of the literature and clinicopathological analysis from the files of the oral pathology department , nihon university school of dentistry at matsudo from 1995 to 2007 of these cases were performed and compared . two cases that had been diagnosed as lipoma with osteo / chondroid differentiation were retrieved from the files mentioned earlier . in these cases , sections of 2 cases were deparaffinized in xylene and dehydrated in tris - buffered saline ( ph 7.6 ) . primary antibodies against e29 ( epithelial membrane antigen ( ema ) ) , qbend 10 ( cd34 class ii ) , ki - s5 ( ki-67 antigen ) , 5.8a ( myo d1 ) were purchased from a commercial source ( dako , denmark ) , and sc-12488 ( runx-2 ) , sc-20095 ( sox-9 ) , sc-71992 ( s-100  chain ) , sc-71993 ( s-100  chain ) , sc-55520 ( fgf-1 ) , and sc-57494 ( vegf ) were purchased from a commercial source ( santa cruz biotechnology , inc , usa ) . for detection of the antigen , the dextran polymer method ( chem mate envision kit , dako , denmark ) was used . to improve detection , the deparaffinized sections were pretreated by microwave heating with citrate buffer ( ph 6 ) . the primary antibodies were generally used at a dilution of 1 : 50 , and the incubation time was 1 hour at room temperature . positive controls consisted of specimens of schwannoma for s-100  and  ; squamous cell carcinoma for ema , cd34 and ki-67 ; ossifying fibroma for fgf-1 and runx-2 , normal lung tissue for sox-9 ; and inflammatory granulation tissue for myod-1 . as a negative control , mouse igg1 ( ki-67 , vegf , cd34 , s-100  ) , igg2a ( ema , s-100  ) and igg2b ( fgf-1 ) , goat igg ( runx-2 ) and rabbit igg ( sox-9 ) were used instead of the primary antibodies . at least 500 nuclei were counted in 5 high - power ( x400 ) fields and ki-67 labeling index was calculated . mean intratumor microvessel density was obtained by calculating the average counts of these 5 fields . the protocol was approved by the committee on studies involving human beings of nihon university school of dentistry at matsudo ( ec 05 - 002 ) . clinical data were retrieved from patient records , and all cases were reviewed microscopically and subclassified . the literature from 1960 to 2008 of lipoma with osseous / chondroid differentiation was reviewed . case 1a 28-year - old woman presented with a painless relatively hard mass on the dorsal surface in the midline of the tongue that had recently grew slightly . the patient 's mother first noticed a tiny nodule when the patient was 6 months old . examination showed a well - defined hard nodular mass , approximately 16    16    9  mm in size , which was sharply demarcated within the muscles of the tongue and freely mobile . a yellowish tinge was visible through the overlying mucous membrane and the lesion was firm on palpation . clinical diagnosis of lipoma with calculus was made and the tumor was completely excised from the tongue under general anesthesia . gross examination showed a yellowish soft to hard smooth mass measuring 16    15    12  mm in size . microscopically , the tumor consisted of a well - circumscribed mass of fatty tissue with a cellular chondroid component . chondromatous nodules within uniform adipose tissue were seen in large areas of mature fat cells supported by fibrous connective tissue ( figure 1 ) . pathological diagnosis was made as lipoma with chondroid differentiation . 
  a 28-year - old woman presented with a painless relatively hard mass on the dorsal surface in the midline of the tongue that had recently grew slightly . the patient 's mother first noticed a tiny nodule when the patient was 6 months old . examination showed a well - defined hard nodular mass , approximately 16    16    9  mm in size , which was sharply demarcated within the muscles of the tongue and freely mobile . a yellowish tinge was visible through the overlying mucous membrane and the lesion was firm on palpation . clinical diagnosis of lipoma with calculus was made and the tumor was completely excised from the tongue under general anesthesia . gross examination showed a yellowish soft to hard smooth mass measuring 16    15    12  mm in size . microscopically , the tumor consisted of a well - circumscribed mass of fatty tissue with a cellular chondroid component . chondromatous nodules within uniform adipose tissue were seen in large areas of mature fat cells supported by fibrous connective tissue ( figure 1 ) . case 2a 59-year - old man presented with a relatively painless hard mass on the left side of the lower labial vestibule surface , which appeared the sense of incompatibility 2 months prior to consultation . examination showed a well- defined hard nodular mass , approximately 5  mm in diameter , and freely mobile , and covered with mucosa of normal aspect and color . there was no tenderness , no sign of inflammation . to retrieve more - detailed relativity with the surrounding tissue , ct was taken and showed a lesion in the left side of the lower lip that appeared to be a small mass with areas of little calcification within . gross examination showed a yellowish soft to hard smooth mass measuring 9    5  5  mm in size . microscopically , the tumor consisted of a well - circumscribed mass of mature fat cells supported by fibrous connective tissue septa and myxoid tissue characterized by spindle cells . a focal island of consecutive chondroid and woven bone component was surrounded by spindle / fusiform - shaped mesenchymal cells throughout the lesion ( figure 2 ) . pathological diagnosis was made as fibrolipoma with osseous / chondroid differentiation . 
  a 59-year - old man presented with a relatively painless hard mass on the left side of the lower labial vestibule surface , which appeared the sense of incompatibility 2 months prior to consultation . examination showed a well- defined hard nodular mass , approximately 5  mm in diameter , and freely mobile , and covered with mucosa of normal aspect and color . there was no tenderness , no sign of inflammation . to retrieve more - detailed relativity with the surrounding tissue , ct was taken and showed a lesion in the left side of the lower lip that appeared to be a small mass with areas of little calcification within . gross examination showed a yellowish soft to hard smooth mass measuring 9    5  5  mm in size . microscopically , the tumor consisted of a well - circumscribed mass of mature fat cells supported by fibrous connective tissue septa and myxoid tissue characterized by spindle cells . a focal island of consecutive chondroid and woven bone component was surrounded by spindle / fusiform - shaped mesenchymal cells throughout the lesion ( figure 2 ) . the patients made an uneventful recovery , and after 15 years ( case 1 ) and 1-year ( case 2 ) follow - up , there was no sign of recurrence . all chondrocytes were stained for s-100  &  , some for runx-2 ( figure 3(a ) ) and some of the outer layer for sox-9 . spindle cells were divided into 2 groups ; peripheral spindle cells around osteo / chondroid tissue and distant spindle cells inside the myxoid area . peripheral spindle cells around chondroid tissue stained diffusely for s-100  &  and sox-9 ( figure 3(b ) ) , though peripheral spindle cells around osteoid tissue only stained for runx-2 ( figure 3(c ) ) . distant spindle cells inside the myxoid area stained diffusely for s-100  and focally for s-100  , myod , sox-9 , and cd34 . as for the number of vessels detected by cd34 , there were 5.0 vessels in this tumor , and there was no differences among the inside areas . none of the cases stained for either ema or fgf-1 or with vegf . between 1995 and 2007 , the files for all cases of oral lipoma at this department showed 909 cases of nonepithelial tumors in the oral soft tissue . of all the lipoma cases , 27 occurred in males and 19 in females ; their mean age was 53.8 years ( range : 2872 years ) . most lesions were located in the buccal mucosa ( n = 16 ) , margin of tongue ( n = 10 ) , lower lip ( n = 7 ) , gingiva ( n = 4 ) ,   and others . microscopically , 28 cases ( 61.0% ) were classified as lipoma and 18 ( 39.0% ) as fibrolipoma . the literature from 1960 to 2008 of lipoma with osseous / chondroid differentiation was reviewed . fourteen reports ( including 16 cases ) were described , and our cases are number 17 and 18 . of all cases , 10 occurred in males and 8 in females ; their mean age was 52.4 years ( range : 2181 years ) . most lesions were situated in the tongue ( n = 6 ) , lower lip ( n = 5 ) and other areas . microscopically , 6 cases ( 33.3% ) had an osseous component , 11 cases ( 61.1% ) had a chondroid component , and 1 case ( our case , 5.6% ) had an osseous / chondroid component . according to our review of the english - language literature , which included our cases , 6 cases were described as lipoma with osseous component [ 57 , 9 , 14 , 15 ] , 11 cases as chondroid component [ 4 , 813 , 16 , 17 ] and 1 case as fibrolipoma with osseous / chondroid components . our case 2 is namely the first report of fibrolipoma with osseous / chondroid differentiation . osteolipomas are less common than chondrolipomas   in the whole body , and almost the same tendency was described in oral lesion . lipoma with osseous / chondroid differentiaion is extremely rare and occurs mainly in large long - standing lipomas [ 15 , 19 ] . case 1 also showed 28-year duration , and this might cause the osseous / chondroid to change into lipoma . as with many tumors , further indistinct etiology of osseous / chondroid change in lipoma has been discussed and most researchers mentioned that their origin is from different types of undifferentiated mesenchymal cells . the hypothesis is that the neoplastic transformation occurs in multipotential undifferentiated mesenchymal cells that later differentiate into lipoblasts , chondroblasts , or osteoblasts and fibroblasts . another hypothesis is that only the adipose cells have a neoplastic transformation , and that the cartilage and bone is produced by differentiation of undifferentiated mesenchymal cells of stroma in chondroblasts or osteoblasts . immunohistochemical results in this study indicated that there was no proliferative characteristic in mesenchymal ( spindle ) cells with small positive rates by ki-67 . chondrocytes and peripheral spindle cells around chondroid tissue with positive findings for s-100  ,  ,   and sox-9 had chondromatous characteristics . sox-9 belongs to the sox ( sry - related high - mobility group box ) family of transcription factors and is a key regulator of developmental processes including chondrogenesis . runx-2 is essential for skeletal mineralization when it stimulates osteoblast differentiation of mesenchymal stem cell and mature chondrocyte differentiation . positive findings for runx-2 in spindle cells around osteoid components and some of chondrocytes indicated osteoblast / chondrocyte characteristics of them . these characteristics are synthesized and thought to be differentiation on account of small positive rate for ki-67 and negative findings for vegf and fgf-1 in this study . osseous / chondroid formation occurred in the central part of these tumors in which a small amount of vessels existed . multipotential undifferentiated mesenchymal cells had undergone differentiation to osteoblast / chondroblast by topical modification , such as nutrition disorder or asphyxia . the bone formation adjacent to chondroid tissue should not be dystrophic calcification because of its positive findings for runx-2 in spindle cells surrounding chondrocytes . these immunohistochemical results supported the conclusion that endochondral ossification and/or perichondral ossification had occurred in these tumor . these results supported lipoma with osseous / chondroid differentiation . lipomas are benign mesenchymal neoplasms composed of mature adipocytes and are rare soft tissue tumors with a 2.2% incidence rate of the whole body . a 20% incidence rate of lipoma has been reported in the head and neck region . a 5% incidence rate in oral lesion of this study showed lower than in the head and neck region , but this rate is almost the same tendency compared to previous reports [ 1 , 20 , 21 ] . the average age of the patient of lipoma was 53.8 years old , and male - to - female ratio was 1.4 : 1.0 in this study . our study supports the current reports that lipomas are generally more common in males than in females ( soft tissue ) , and occurred in adult patients most often between the ages of 40 and 60 years [ 1 , 3 ] . the predominant locations were the buccal mucosa and the margin of the tongue and the lower lip , where there is plenty of adipose tissue . the patients ' characteristics and location distribution , cheek and tongue , were similar to previous reports [ 1 , 20 , 22 ] . microscopically , 28 cases ( 61.0% ) were classified as lipoma and 18 ( 39.0% ) as fibrolipoma . fujimara   have reported , but our case 2 is the first report of fibrolipoma with osseous / chondroid differentiation . the two cases this reports contributed to pile up of rare lipoma / fibrolipoma with osseous / chondroid differentiation case , and , in addition , immunohistochemical result is contributed to the clarification of the etiology .
the purpose of this study was to determine the clinicopathological and immunohistochemical features of lipoma / fibrolipoma with rare occasions as osseous and/or chondroid differentiation in the oral cavity . 
 two cases of the tumors , who presented with a painless , relatively hard mass on the oral mucosa , were studied . 
 these were consisted of a well - circumscribed 
 mass of fatty tissue with chondroid and significant fibrous component intermixed with the lobules of fat cells with chondroid and woven bone 
 component , respectively . 
 immunohistochemical study revealed that peripheral spindle cells around chondroid tissue stained diffusely for s-100  &  and sox-9 , though peripheral spindle cells around osteoid tissue only stained for runx-2 . according to review of the literature , 
 lipoma / fibrolipoma with osseous and/or chondroid differentiation was 18 cases . 
 also fibrolipoma with osseous and chondroid differentiation is the first to be reported here . 
 these results indicated that the cartilage / bone is produced by differentiation of undifferentiated mesenchymal cells of stroma .