it develops most of the time on the skin ; however , other parts of the body could be involved , including the oral cavities . oral malignant melanoma ( omm ) , unlike cutaneous melanoma , is considered a rare lesion with an incidence of 0.4 - 1.8% of all melanomas and 0.5% of all oral malignancies . the etiology of omm is still not defined , contrarily to cutaneous melanoma for which sunlight and genetic background are considered etiologic factors . the most frequently affected oral sites are the palate and the maxillary gingiva ; other less frequently affected sites include the labial and buccal mucosa as well as the tongue . black africans , japanese , and native americans are more commonly affected than the european population . histologically , melanomas are characterized by proliferation of malignant melanocytes arranged along the basal layer , having the potential for tissue invasion and metastasis . these cells show a considerable pleomorphism , with a wide range of shapes , such as round to spindled , plasmacytoid , clear cell and epithelioid , and have a solid , alveolar , organoid or pagetoid pattern . necrosis , lack of an inflammatory reaction , and not always detectable mitotic activity are other histological features of this disease . the purpose of this report is to describe a case of omm and to emphasize the importance of histological examination . an 80-year - old woman was referred to our clinic for evaluation and treatment of a pigmented oral lesion . intraoral examination showed multiple lesions represented by macules and nodules on the hard and soft palate , superior alveolar mucosa and gingiva ( fig . a biopsy , which included the free and attached gingiva and alveolar mucosa was performed and submitted to histopathological analysis . 2a , b ) showed sheets and nests of melanocytes , some with round , plasmacytoid or epithelioid morphology in the superficial corium extending to the deep tissues . some of them presented round nuclei of various sizes , occupying nearly the entire cell cytoplasm and prominent nucleoli . 3d ) and negative for ae1/ae3 ( not shown ) , confirming the diagnosis of melanoma . the patient refused a complete workup examination ( i.e. ct scan , mri , etc . ) as well as any type of treatment and died 11 months later . we presented a case of omm which was initially misdiagnosed as a probable racial pigmentation elsewhere 2 years earlier . this diagnosis was made by taking only the clinical aspect into account and without performing histological analyses . acquired and small congenital nevi show a high frequency of braf mutations . in cutaneous melanoma , nevertheless , there is no report in the literature about the potential malignant transformation rate of oral melanocytic nevi or other pigmented lesions . in our case , we can not establish if the melanoma arose de novo or from a preexistent benign pigmented lesion or precursor , since a biopsy was not carried out . therefore , all suspicious lesions presenting an asymmetric , irregular form , with variation in color and diameter should be investigated in order to obtain a definitive diagnosis . the differential diagnosis for pigmented lesions includes tattoos , oral melanotic macule , racial pigmentation , nevi , melanoacanthoma , melanoma and systemic diseases such as polyostotic fibrous dysplasia , neurofibromatosis , multiple endocrine neoplasia syndrome , peutz - jeghers syndrome , and addison 's disease . initially , omm appears as an asymptomatic lesion characterized by a flat macule , or a slightly elevated lesion that may later become elevated and develop signs and symptoms such as swelling , ulceration , bleeding , pain and tooth mobility . according to the literature , swelling is considered the main reason for consultation , followed by bleeding , ill - fitting dentures , pain , increased mobility of teeth and delayed healing of extraction sockets . omm occurs in adults of all ages , but it is most common in the elderly . when studying 187 cases , showed an average age of 67.5 years , and an unusual case of a 9-year - old patient was described by loreno et al . . there is no agreement in the literature concerning the ratio of the patients ' gender , having no sex predilection or presenting a slight predilection for men or sometimes for women . histologically , the tumor cells show a considerable pleomorphism , with a wide range of shapes and patterns that could mimic other tumors such as lymphomas , poorly differentiated carcinomas , neuroendocrine carcinomas , sarcomas , and germ - cell tumors . in addition , more rarely , the melanomas may be nonpigmented , causing difficulties in clinical diagnosis and are typically diagnosed at a later stage . therefore , the use of immunohistochemical staining is an important tool to help distinguish melanomas from other malignancies . the helpful markers of melanoma diagnosis are s-100 , hmb-45 , melan - a , and tyrosinase . for this case , we used s-100 , hmb-45 and melan - a . s-100 is very sensitive ( around 97 - 100% ) but not very specific ( 75 - 87% ) . some carcinomas , sarcomas ( such as rhabdomyosarcomas , leiomyosarcomas , and peripheral nerve sheath tumors ) , and langerhans cell histiocytosis can be positive for s-100 . hmb-45 recognizes a type i membrane - bound melanosomal protein called pmel17 or gp100 protein . the analysis of hmb-45 and ki-67 antibodies can be useful for distinguishing primary cutaneous melanomas from some nevi . ki-67 is a marker of tumor cell proliferation , which is commonly used as a complement to distinguish benign nevi from melanoma . with less than 5% of positive cells , the lesion is considered as benign nevi , while with 13 - 30% of positive cells , it is considered as malignant melanoma . in our case the multi - cytokeratin ( ae1/ae3 ) antibody is reported to be characteristic of epidermal cells . many predictors of prognostics have been proposed in the literature on omm such as age , clinical stage , depth of invasion and vascular invasion . however , because of the rarity of this disease , consensus criteria have not yet been established . according to the microstaging classification by prasad et al . , which is based on the invasion of the tissue within the mucosa , level i is defined as melanoma in situ , level ii as melanoma invading up to the lamina propria and level iii as melanoma with deep tissue invasion . our case was classified as level iii because the malignant melanocytes reached the periosteum . however , there was no invasion of blood vessels and nerve fibers . melanoma has an initial phase named radial or horizontal growth , which is characterized by a laterally spreading growth of malignant melanocytes only within the epithelium , representing the in situ stage . later , in the vertical growth phase , there is an invasion of the underlying tissues . omm is normally diagnosed in the vertical growth pattern , which may explain its very poor prognosis . in this case , the patient refused any type of treatment and died 11 months after the diagnosis . it has been shown that early identification of the melanoma and its treatment by radical surgery comprise the most important treatment strategy . an association with adjuvant radiation can also be performed . in cases of metastatic diseases , chemotherapy should be considered with the aim of improving the survival of patients with head and neck melanoma . due to the deadly behaviour of omm , showing a poor prognosis with a 5-year survival rate of 15% , all focally pigmented lesions and most diffusely pigmented lesions require a biopsy for diagnosis .