melanoma is the malignant tumor of melanocytes which may present in a wide morphological spectrum including highly pigmented to amelanotic appearance . clinically there are four main subtypes of cutaneous melanoma : superficial spreading melanoma , lentiginous melanoma , nodular melanoma and acral lentiginous melanoma .
the diagnosis of amelanotic variants of melanoma may especially be challenging both clinically and histologically .
in addition to clinical variants of melanoma , in the literature various atypical histological variants of melanoma have been reported , such as fibroblastic , desmoplastic , chondroid , osteoid , and myxoid melanoma , which were classified according to stromal changes [ 13 ] .
myxoid melanoma is an unusual variant of malignant melanoma , which is characterized by atypical spindle cells and dense mucin deposition in dermis .
the prevalence of this melanoma variant is not well known and may develop on cutaneous or extracutaneous sites , including the sino - nasal passages .
this tumor may be confused with other mucin - containing neoplasms , histologically benign or malignant , and clinically is usually reported in elderly people with a similar progress to other variants of melanoma .
a 28-year - old male presented to our outpatient clinic with a history of an asymptomatic pink nodule which had been growing slowly for last 6 months . dermatological examination revealed a 2.5 x 2 cm diameter pink , mildly infiltrated tumoral lesion with two pigmented papular lesions on left arm ( figure 1 ) .
dermoscopic examination revealed pink - white cristalline structures and blue - grayish ovoid globules ( figure 2 ) .
the lesion was totally excised with 3 mm margins with the initial diagnosis of basosquamous carcinoma , amelanotic melanoma and basal cell carcinoma .
histopathological examination was consistent with myxoid melanoma with breslow thickness 11.6 mm , clark level v ( figure 3a , b ) .
there was no vascular , lymphatic or perineural invasion histologically , and mitoses 2/1 per mm .
strong positivity was detected with s100 and hmb45 staining , and widespread positive staining was detected with pas - alcian blue for mucin deposition ( figure 4a , b ) .
laboratory tests , including complete blood count , routine biochemistry , lactate dehydrogenase and beta-2 microglobulin and imaging test for metastasis , including pet - ct and sentinel lymph node biopsy , were all clear .
the patient is currently well and clinically free of recurrence 18 months after the diagnosis .
the presence of myxoid stroma in malignant melanoma was first published by bhuta et al in 1986 in four metastatic malignant melanomas .
clinically these tumors were reported to be amelanotic , but in some cases melanogenesis was also shown with fontana masson preparations .
histologically , this rare variant of melanoma is characterized by large malignant melanocytes and a basophilic mucinous matrix . in all cases ,
the myxoid stroma is comprised of mesenchymal acidic mucopolysaccharides , as opposed to neutral epithelial mucins .
mucinous material is usually located around the tumor cells , as in our case , but not within the tumor cells as in cytoplasmic localization , confirming that the myxoid matrix is produced as a response to the stromal cells in the tumor rather than being a product of the tumor cells .
myxoid changes are more often reported in metastatic tumors than in primary malignant tumors , but in our patient due to the completely intradermal location of tumor cells with no junctional component , ith a nodular architecture , features of malignancy , no ulceration , the absence of peripheral nerves , and an absence of preexisting melanocytic nevus , he was diagnosed as primary dermal melanoma . additionally , based on the histopathologically myxoid stromal changes ,
he was diagnosed as primary myxoid melanoma . also no other metastatic or primary malignant lesion
typically , s100 staining is strongly positive , but immunostaining with hmb-45 is less uniform and both positive and negative results were reported in the literature . in our patient both s100 and hmb45 staining were strongly positive .
the differential diagnosis of myxoid melanoma is broad , including several other benign and malignant myxoid neoplasms of soft tissue as well as epithelial cancers such as myxoid liposarcoma , myxoid malignant fibrous histiocytoma , low - grade fibromyxoid sarcoma , myxoid chondrosarcoma , myxoid peripheral nerve sheath tumors , dermatofibrosarcoma protuberans and metastatic adenocarcinomas .
the clinical and the prognostic significance of mucin deposition in melanomas is challenging due to presence of myxoid material both in primary benign or malignant tumors .
some authors claimed that mast cells and secretion of transforming growth factor beta stimulates fibroblast secretion of mucin contributing to the tumor s invasive potential ; however , in the absence of compelling contrary data , the current series of cases suggests that myxoid stroma is more significant in diagnosis rather than prognosis of myxoid melanoma .
although the real importance of myxoid changes in tumors is not well known , awareness of this stromal pattern in malignant melanomas may prevent misdiagnosis and therapeutic errors .
 myxoid melanoma is a rare variant of melanoma , which is characterized by atypical spindle cells and dense mucin deposition in dermis . 
 this tumor is usually seen in elderly people with a similar progress in other variants of melanoma.a 28-year - old male presented to our outpatient clinic with a 6-month history of a slowly growing asymptomatic pink lesion on his arm . 
 dermoscopic examination revealed pink - white cristalline structures and blue - grayish ovoid globules . 
 the lesion was totally excised with initial diagnosis of basosquamous carcinoma , amelanotic melanoma and basal cell carcinoma . 
 histopathological examination was consistent with myxoid melanoma.we present this case due to the rarity of myxoid melanoma and occurrence at such a young age . 