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malignant fibrous histiocytoma ( mfh ) is the most common soft tissue sarcoma of late adult life , and it is rare in young patients .
it usually involves the deep soft tissues and the striated muscles of the proximal part of the extremities , particularly the lower extremities .
up to 25% of cases may arise in subcutaneous tissues , although less than 10% are confined to the subcutis without underlying fascial involvement .
although afx is histologically indistinguishable from mfh , afx invariably shows a more favorable prognosis that results from its superficial location .
more recently , o13 ( cd99 ) was found to display immunoreactivity in cases of afx , but it was negative for mfh .
cd99 , also known as p30/32 glycoprotein or mic-2 protein , is a cell surface protein encoded by genes on the x and y chromosomes .
it has been shown to be reactive in ewing 's sarcoma , primitive neuroectodermal tumors , some lymphomas , and other mesenchymal tumors .
it is also reported that cd99 expression may be associated with the biologic behavior of some tumors because of its roles in t cell apoptosis .
metastasis of mfh occurs most in the lung ( 90% ) , followed by bone ( 8% ) and liver ( 1% ) . concerning skin metastasis ,
only 8 cases of mfh with cutaneous metastasis were previously reported , and no cases of in - transit metastasis of mfh have been reported in the english literature so far . here , we describe a case of mfh with in - transit metastasis . similar to previous reports , this case suggests the importance of an accurate diagnosis for the prediction of prognosis .
a 30-year - old man in good health presented to our department with a 3-year history of an asymptomatic , enlarging tumor on his scalp .
the tumor was excised by a private physician 8 years before , but had recurred .
physical examination revealed a skin - colored , elastic hard , well - demarcated tumor on the left side of his occipital region ( fig .
moreover , there was an elastic hard , satellite nodule located 4 cm from the tumor .
biopsy specimens taken from the tumor revealed a significant number of minimal atypical spindle or stellate cells in the middle to deep dermis ( fig .
immunohistochemistry showed that a significant number of factor xiiia - positive cells was disseminated in the tumors ( fig .
the findings of the laboratory evaluation , including complete blood count , liver function tests and urinalysis , were all within normal limits .
histopathology revealed that the main bulk of the tumor was located from the dermis to the subcutaneous tissue ( fig .
the dermal lesion consisted of minimal atypical spindle or stellate cells and foam cells within myxoid matrices ( fig .
the satellite nodule was composed of densely proliferating spindle cells with moderate pleomorphism arranged in a haphazard fashion ( fig .
3e ) , and , in contrast to the primary tumor , the satellite lesion was located in the subcutaneous tissue ( fig .
immunohistochemically , both the primary tumor and the satellite nodule were positive for vimentin and cd31 + , and negative for sma , s100 , desmin , hmb-45 , melan - a , ae1/ae3 , and cam5.2
. from these results , we made the diagnosis of mfh with in - transit metastasis in our patient .
we examined for possible distal metastasis by computed tomography scan , and detected no metastasis .
five years after the surgical treatment , there was no evidence of local recurrence or metastasis .
we present a case of mfh with in - transit metastasis . in the present case ,
the primary tumor was mainly located in the dermis , similar to the cutaneous form of mfh , also known as afx . as the metastasis of mfh occurs mainly through tumor vessels ,
it is difficult to ascertain the biological behavior of mfh in the skin . in general , the prognosis of mfh is suggested to depend on the size of the initial lesion , as well as the depth of the tumor and the histological grade .
superficial tumors of less than 5 cm in diameter have an excellent prognosis . on the other hand , high - grade lesions situated deep in the skeletal muscle and measuring more than 10 cm in size are at great risk of metastasis . in our case ,
the primary tumor was mainly confined to the dermis , had not penetrated into the muscle fascia and was less than 5 cm in diameter ; however , local recurrence with in - transit metastasis occurred 8 years after the primary resection of the tumor .
because recurrence is frequently due to misdiagnosis of the proliferation as benign , our case strongly suggests the importance of a precise diagnosis and a complete resection of the primary tumor in the initial phase .
recently , hartel et al .   reported a higher proportion of cd99 positivity in afx compared with mfh ( 94 vs. 15% ) and that the degree of cd99 expression is in part related to their different biologic behaviors . since
cd99 has been shown to play a role in t cell apoptosis , they concluded that the strong cd99 expression in afx may be pathogenetically associated to some degree with a more effective apoptosis of tumor cells and , therefore , correlate with a benign clinical course . in our case , only a slight expression of cd99 was observed both in primary and in - transit metastatic lesions .
in other words , the lack of cd99 expression in our case may have been the cause of the in - transit metastasis of the primary tumor . regarding treatment , initial wide excision
is recommended because of the tendency for local recurrences , which generally increases the risk of metastasis . in the present case ,
no recurrence occurred over a period of 5 years ; however , there was in - transit metastasis together with a history of local recurrence .
malignant fibrous histiocytoma ( mfh ) is the most common fibroblastic tumor , but its cutaneous metastasis , especially in - transit metastasis , is extremely rare . 
 we describe the case of a 30-year - old japanese man with a recurrent mfh on the scalp accompanied by in - transit metastasis , which had been treated as a benign skin tumor 8 years before . 
 the main bulk of the recurrent tumor was located in the dermis , but the metastatic tumor was mainly located in the subcutis . 
 generally , atypical fibroxanthoma , also known as cutaneous mfh , is rarely metastasized and presents a benign clinical course . 
 since there is a great difference between the prognosis of mfh and atypical fibroxanthoma , precise diagnosis of the primary tumor is essential .