malignant melanoma is a malignant tumor of the melanocytes or the cells that develop from melanocytes . histologically , malignant melanomas are asymmetrical and poorly circumscribed lesions with architectural disturbance and usually marked cytological atypia . the major histologic subtypes of melanoma are superficial spreading melanoma , nodular melanoma , lentigo maligna melanoma and acral lentiginous melanoma , which show a variety of cytomorphological features , architectural patterns and stromal changes that may be observed in malignant melanomas . moreover , there are numerous uncommon histological variants , including clear , signet ring , pseudolipoblastic , rhabdoid , plasmacytoid and balloon cell melanomas . among them , balloon cell malignant melanoma ( bcmm ) is the rarest variant composed of large , polygonal , foamy cells with abundant cytoplasm . these features can also be seen in balloon cell nevus ( bcn ) , but the presence of nuclear pleomorphism , atypia , mitoses and a lack of maturation of melanocytes with descent into the dermis help to differentiate bcmm . a balloon cell change may occasionally be observed in conventional melanomas , but it mostly remains in focal areas . malignant melanoma accounts for only 35% of primary cutaneous malignancies and it mostly develops in people over 50 years . this report presents a young patient of primary bcmm with near - complete effacement by foamy cells . a 32-year - old female presented to our hospital with a tumor on the left lumbar region . the lesion of concern was an erythematous and focal eccentric pigmented nodule of 15 mm in diameter ( fig . the clinical appearance of the lesion raised a suspicion of malignancy , and surgical resection was performed . the surgically resected specimen showed a nodule with focally pigmented areas , and the cut surface of the nodule was asymmetrical and not ulcerated . histological examinations showed a skin fragment with nearly complete effacement by foamy cells and asymmetry ( fig . the foamy cells in the superficial dermis extended to the fatty tissue to a depth of 10 mm . 1c ) . the intraepidermal component was composed of both nested and single atypical melanocytes with areas of intraepidermal pagetoid spread ( fig . the pathological diagnosis was of bcmm ( breslow depth 10 mm , clark level v ) without ulcer . a month after the excision , the excised bilateral inguinal lymph nodes showed diffuse replacement of the lymph nodes by foamy cells ( fig . bcmm is an uncommon histopathological subtype of malignant melanoma that was first described by gardner and vazquez in 1970 . , balloon cell changes of melanocytes have been noted in numerous neoplasms , including melanoma . histologically differential diagnosis of bcmm includes bcn , clear cell sarcoma , clear cell metastatic renal cell carcinoma , basal cell carcinoma , squamous cell carcinoma and dermatofibroma . the clinical appearance could also be interpreted as that of spitz nevus , basal cell carcinoma , eccrine poroma or eccrine porocarcinoma . a microscopic examination showed a dominant nodular component comprised exclusively of markedly distended epithelioid melanocytes showing abundant vacuolated cytoplasm . bcmm differs from bcn in its nuclear pleomorphism , atypia and the lack of melanocyte maturation with a decent proliferation into the dermis . while fontana - masson staining of melanoma cells is generally positive , balloon cells in bcmm are generally negative in this stain [ 4 , 5 , 6 , 7 ] the balloon cell component of our current case was also stained negative with fontana - masson . the occurrence of the foamy cells has been suggested to be related to an enlarged defective melanosome formation . they are likely developed by the transformation of epithelioid cells , because balloon cells are mainly observed at metastatic or recurring lesions . previous case reports suggested that patients with bcmm may have longer survivals than those without balloon cell changes . however , the actual mortality rate of bcmm tends to be high because bcmm are thick at the time of presentation . in fact , there was no apparent difference in a more recently reported survival rate between bcmm and other variants of melanoma . malignant melanoma may affect people of all ages but is mostly observed in people over the age of 50 years . the case reported here is a young case of primary bcmm with near - complete effacement by foamy cells .
balloon cell malignant melanoma ( bcmm ) is a very rare malignant melanoma subtype . the clinical appearance of bcmm varies ; it may be nodular , ulcerated , polypoid , papillomatous and often non - pigmented . 
 the tumor cells histologically appear large , polygonal or round and contain abundant granular or vacuolated cytoplasm . 
 we herein report the case of a 32-year - old female who presented with a focal eccentric pigmented mass in the left lumbar region of 15 mm in diameter that had been present for several years . 
 she underwent tumor excision . 
 the histopathological analysis showed epithelioid melanocytes with clear cytoplasm . 
 an immunohistochemical analysis revealed that the cells were positive for hmb-45 and s-100 protein and negative for cytokeratin . 
 the balloon cell component stained negative for fontana - masson . a month later , 
 the patient underwent excision of the bilateral inguinal lymph nodes and metastatic bcmm was revealed . 
 the lymph node metastases showed the complete replacement of lymph nodes by balloon cells . 
 a diagnosis of bcmm ( breslow depth 10 mm , clark level v ) without ulcer was rendered . staining with 
 ki-67 was positive in almost 44% of the balloon cells .