Fibrohistiocytic differentiation in subcutaneous fatty tumors

Abstract

Subsets of dendritic cells, fibroblasts which express the human progenitor cell antigen CD34 or histiocytes which express coagulation factor XIIIa (FXIIIa), are present in fat and in collagenous connective tissue. As components of the microvascular unit, these fibrohistiocytic cell subsets may interact during stromal remodeling, repair, and neoplasia. We studied white fat and subcutaneous fatty tumors to determine if CD34 and/or FXIIIa+ "fibrohistiocytic" dendritic cell subsets are involved in their morphogenesis. Three lipomas (L), 1 intramuscular lipoma (IL), 1 myxoid lipoma (ML), 2 pleomorphic lipomas (PL), 2 spindle cell lipomas (SCL), 8 angiolipomas (AN) in 4 patients, 1 atypical lipoma/well-differentiated liposarcoma (AL), 1 de novo dedifferentiated liposarcoma (DL), and 1 recurring atypical myxoid signet ring lipomatous tumor were examined for CD34, FXIIIa and in some cases for CD31, desmin, Ki 67, or S-100. Normal fat has scattered CD34+ dendritic cells and small FXIIIa+ dendritic histiocytes among variably S-100+ adipocytes. The CD34 and FXIIIa+ dendritic cells are more numerous near vessels and within fibrovascular septae. In L and IL, CD34 and FXIIIa+ dendritic cells are activated and some adipocytes express CD34. Mesenchymal areas of SCL, PL, ML, and AL and DL are composed of CD34+ dendritic cells with CD34+ but FXIIIa-negative floret cells in PL or atypical cells in AL and DL. FXIIIa+ dendritic cells are numerous in these lesions, comprising 30-40% of cells in SCL and PL, and 50% in ML, AL, and DL. AN have focal CD34+ interstitial cells and plump FXIIIa+ cells that in one case resembled multivacuolated lipoblasts. The myxoid signet ring lipomatous tumor was CD34 negative with few FXIIIa+ cells. We conclude that subsets of CD34+ and FXIIIa+ dendritic microvascular cells are present in normal fat and proliferate together in various types of lipomas and in at least some dedifferentiated liposarcomas.

Persistence of CD34 Stem Marker in Human Lipoma: Searching for Cancer Stem Cells

“…The presence of CD34 + cells in lipomas is well-known 8 and is used to confirm the histological diagnosis 9 , 10 . A varying amount of CD34 + spindle cells is generally detectable within the lesion 11 , 12 : they are more numerous near vessels 13 , whereas the adipocytes and the other differentiated cells are negative for CD34 expression 14 , leading to the hypothesis of an abnormal proliferation of normal CD34 perivascular cells in various types of lipomas and some liposarcomas 13 . A proliferation of CD34 + dendritic cells in a variety of fibrovascular and fibrohistiocytic tumours has been reported 15 and hypothesized for Kaposi's sarcoma, also too 16 .…”

Spindle cell lipoma in an intramuscular lipoma

“…In embryonic specimens, by 6 weeks, there is a band of CD34+ dendritic cells at the junction of the deep reticular dermal and subcutaneus anlagen. This distribution suggests that the CD34+ deep dermal dendrocytes might contribute to the formation of the primitive fat organ 11 . These studies might be a useful clue to understanding why the spindle cells of SCL give a strong reaction with CD34.…”

“…The SCL are thought to arise from a fibroblast‐like primitive adipocyte precursor cell shown in electron microscopy studies of fat and conventional lipoma as pericytic cells present along the interstitial capillaries 11 . In embryonic specimens, by 6 weeks, there is a band of CD34+ dendritic cells at the junction of the deep reticular dermal and subcutaneus anlagen.…”

Intramuscular Lipoma of the Sternocleidomastoid Muscle: A Rare Entity Revisited

“… 7 Another interesting theory is the fibrohistiocytic differentiation of cells in fatty tumors: CD34 + perimysial fibroblasts and interstitial dendritic cells appear to undergo an adipocytic transformation, contributing to the pathogenesis of intramuscular lipomas. 8 Moreover, an immunohistochemical study demonstrated that structures within the head and neck region are abundantly covered with CD34 + fibrous tissues, especially the parotid gland and the sternocleidomastoid muscle. 9 This can potentially explain how an intramuscular lipoma could have arisen within the SCM muscle.…”