plexiform fibrohistiocytic tumor ( pft ) presents as a slowly developing nodule on the extremities and trunk [ 1 , 2 ] , and generally occurs in children and young adults [ 1 , 2 ] . although approximately 150 cases have been presented in english language papers about pft [ 1 , 2 , 3 , 4 ] , little is known about its pathogenesis . a 28-year - old japanese woman visited our outpatient clinic with a 1.5-year history of an asymptomatic nodule developing on her left retroauricular skin . her tumor had been resected by a general surgeon as a benign spindle cell tumor without further histological diagnosis 1 year before . on her initial visit , physical examination revealed a well - demarcated nodule on her retroauricular skin , 20  20 mm in size ( fig . 1a ) . magnetic resonance imaging revealed a subcutaneous nodule located adjacent to the periosteum ( fig . the histopathological findings revealed proliferation of fibroblastic and histiocytic cells showing storiform - type whorling and a plexiform pattern ( fig . these tumor - composing spindle cells were positive for cd68 and sma , and negative for s100 and factor xiiia . the differential diagnoses of pft are listed in table 1 . since the pathogenesis and biological behavior of pft are still incompletely understood , we employed immunohistochemical staining for periostin ( postn ) , cd163 and cd206 to further investigate the possible immunological background of the pft . a dense deposition of postn was detected throughout the stromal areas of the tumor ( fig . in addition , cd163+cd206 tumor - associated macrophages ( tams ) were densely infiltrated in the same areas of postn ( fig . in this report , we describe a case of pft on the ear which showed a dense deposition of postn in the stromal areas of the tumor . pft is a rare mesenchymal neoplasm of intermediate malignant potential with a high local recurrence rate , like dermatofibrosarcoma protuberans [ 1 , 2 , 3 , 4 ] . immunohistochemical staining is helpful for the differential diagnosis of pft [ 1 , 2 ] : e.g. it is positive for cd68 , vimentin and nse , and negative for s100 , cd34 , factor xiiia and calponin [ 2 , 3 ] . since these diagnostic markers for pft do not reflect the biological behavior of this type of malignant tumor , in this report we employed immunohistochemical staining for postn as well as cd163 and cd206 , focusing on the cancer stroma of pft to investigate the possible mechanisms of local invasion and recurrence of pft . postn is an extracellular matrix protein that is involved in modulating cell functions through various pathways [ 5 , 6 , 7 ] . in the dermatological field , the deposition of postn is reported in various skin diseases , including fibrosing diseases such as keloid , hypertrophic scar , morphea and lichen sclerosis et atrophicus . zhou et al .   reported the importance of postn in developing glioblastoma multiforme by the induction of m2-like tams in the tumor microenvironment . in addition , as we previously reported , postn stimulates cd163+cd206 monocyte - derived macrophages to produce a series of chemokines that might be connected with the cancer formation of mycosis fungoides . notably , this study also suggests that cd163+cd206 monocyte - derived macrophages augment the mrna expression of mmp12 by postn stimulation . interestingly , mmp12 is reported to be increased in the serum and skin lesions of systemic sclerosis , and is associated with the severity of skin and pulmonary fibrosis . these reports suggested the significance of the postn / tams axis in the progression of various types of tumors , and suggested that postn stimulation might modulate the function of cd163+cd206 tams to develop the fibrosis in pft . to confirm this hypothesis
plexiform fibrohistiocytic tumor ( pft ) is a rare mesenchymal neoplasm of intermediate malignant potential with a high local recurrence rate . in this report 
 , we describe a case of pft on the ear , which showed a dense deposition of periostin ( postn ) in the stromal areas of the tumor . 
 in addition , dense infiltration of cd163+cd206 tumor - associated macrophages ( tams ) was detected in the same areas as postn . since postn was previously reported to possess immunomodulatory effects on tams , 
 our present report suggested the significance of the postn / tams axis in the progression of pft .