Human Progenitor Cell Antigen Research Articles

Effects of Botulinum Toxin Type A on Microvessels in Hypertrophic Scar Models on Rabbit Ears.

Background Although Botulinum Toxin Type A (BTXA) has been applied to scar prevention and treatment, the mechanisms still require further exploration. Objective To investigate the effects of BTXA on microvessels in the hypertrophic scar models on rabbit ears. Methods Eight big-eared New Zealand rabbits (males or females) were selected to establish scar models. One ear of each rabbit (4 models in each ear) was selected randomly to be injected with BTXA immediately after modeling and included in the treated group, while the opposite ear was untreated and included in the control group. The growth of scars in each group was observed and recorded, and 4 rabbits were sacrificed on days 30 and 45 after modeling. Then, scar height was measured by hematoxylin-eosin (HE) staining, vascular endothelial growth factor (VEGF) expression was detected by immunohistochemical (IHC) testing, and microvessel density (MVD) was calculated based on CD34 (human hematopoietic progenitor cell antigen). Results The wounds in each group were well healed and free from infection or necrosis. On days 30 and 45, the scar height, MVD value, and VEGF expression in the treated group were lower than those in the control group (P < 0.05). For the treated group, the above indicators on day 45 were lower than on day 30 (P > 0.05). Besides, there was a positive correlation between the MVD value and the VEGF expression in the treated group (P < 0.05). Conclusion The injection of BTXA immediately after modeling inhibits VEGF expression and reduces angiogenesis, thereby inhibiting hypertrophic scar formation.

MicroRNA profile of hepatic epithelioid hemangioendothelioma: A case report.

A 72-year-old female was referred for further evaluation of epigastralgia. Abdominal contrast computed tomography revealed numerous tumors in the two lobes of the liver. Liver biopsy and immunohistochemical staining revealed that the tumor cells were positive for factor VIII-associated antigen, platelet endothelial cell adhesion molecule 1 and human hematopoietic progenitor cell antigen, concordant with a diagnosis of hepatic epithelioid hemangioendothelioma (HEH). To elucidate the etiology of HEH, particularly the microRNA (miRNA) profiles, tissue samples obtained from normal and tumor tissues were analyzed using a miRNA array system. A total of 14 miRNAs were significantly upregulated and 93 miRNAs were downregulated in the tumor tissues (P<0.01). Additionally, unsupervised hierarchical clustering analysis using Pearson's correlation revealed that the tumor tissues clustered separately from the normal tissues. The miRNA expression profile was analyzed in HEH and compared with angiosarcoma, which exhibits histology similar to HEH. Out of a total of 107 miRNAs, only miR-122-5p and miR-1290 demonstrated a differential expression pattern in angiosarcoma. Therefore, these miRNAs may be novel biological markers for the determination of a diagnosis of HEH in primary mesenchymal tumors of the liver. To the best of our knowledge, this study is the first report of a miRNA microarray analysis in HEH.

De novo protein sequencing, humanization and in vitro effects of an antihuman CD34 mouse monoclonal antibody

QBEND/10 is a mouse immunoglobulin lambda-chain monoclonal antibody with strict specificity against human hematopoietic progenitor cell antigen CD34. Our in vitro study showed that QBEND/10 impairs the tube formation of human umbilical vein endothelial cells (HUVECs), suggesting that the antibody may be of potential benefit in blocking tumor angiogenesis. We provided a de novo protein sequencing method through tandem mass spectrometry to identify the amino acid sequences in the variable heavy and light chains of QBEND/10. To reduce immunogenicity for clinical applications, QBEND/10 was further humanized using the resurfacing approach. We demonstrate that the de novo sequenced and humanized QBEND/10 retains the biological functions of the parental mouse counterpart, including the binding kinetics to CD34 and blockage of the tube formation of the HUVECs.

A protocol for enrichment of CD34+ stromal cell fraction through human skin disaggregation and magnetic separation

A protocol for enrichment of CD34+ stromal cell fraction through human skin disaggregation and magnetic separation

Medallion-like dermal dendrocyte hamartoma in a 36-year-old male

Medallion-like dermal dendrocyte hamartoma in a 36-year-old male

α‐Smooth muscle actin immunoreactivity may change in nature in interlobular fibrosis of the pancreas in patients with congenital biliary dilatation

Pancreatic fibrosis in patients with congenital biliary dilatation (CBD) or choledochal cyst was studied to determine why biliary pancreatitis seldom progresses to chronic pancreatitis/more progressive state. Pancreatic collagenization in eight patients (three adults with pancreatoduodenectomy and five children with biopsy of the pancreas performed when excising the cyst) with CBD was evaluated histopathologically and immunohistochemically. Interlobular and periductal fibrosis with both collagen Type I and Type III immunoreactivities was found in six out of eight cases and in all four cases in which the pancreatic duct was included, respectively. The interlobular area was seldom immunoreactive for alpha-smooth muscle actin (alpha-SMA), a marker for myofibroblasts, but was usually positive for CD34, a human progenitor cell antigen. In contrast, the periductal area was usually immunoreactive for alpha-SMA, but usually negative for CD34 and immunopositive for bcl-2, indicating a continuously progressive state of fibrosis, in which 'pre-existing'alpha-SMA immunoreactivity in the interlobular area may change in nature and lead to CD34-positive fibrosis or apoptosis. In conclusion, biliary pancreatitis is not likely to evolve into chronic pancreatitis/more progressive state because 'pre-existing'alpha-SMA immunoreactivity in the interlobular area may change in nature.

Human dental pulp vasculogenesis evaluated by CD34 antigen expression and morphological arrangement.

Vasculogenesis describes the process by which endothelial precursor cells form new blood vessels. To characterize the topography and the cellular processes underlying vascularization of human dental pulp, we examiend the expression of the human hematopoietic progenitor cell antigen CD34. Dental pulps, obtained from deciduous and permanent teeth, were morphologically examined at light- and electron-microscope levels and by expression of CD34. The findings indicate that vasculogenesis of dental pulp is a complicated process starting from single CD34(+) cells. These subsequently coalesce to form solid vascular cords inside the developing connective tissue, which later hollows. Pericytes were embedded within the fully formed microvessels' basement membrane. The presence of CD34(+) endothelial cells in permanent teeth reveals that the process of vasculogenesis persists into adult life, where it contributes to continuous adjustment of vessel and network structures in response to functional needs and dental tissue homeostasis.

Solitary fibrous tumor of renal pelvis

A 70-year-old Japanese man was referred because of a right renal mass of 2 years in duration. Imaging studies, including magnetic resonance imaging, revealed an ovoid mass, with relatively abundant vascularity, in the right renal pelvis. Right radical nephrectomy was done and a tumor measuring 6.0 x 4.5 x 4.0 cm was found in the renal pelvis. Solitary fibrous tumor (SFT) was highly suspected by histology. Immunohistochemical study using a monoclonal antibody directed against the human hematopoietic progenitor cell antigen (CD34) stain confirmed SFT. This is the first case of SFT of the renal pelvis. Although SFT is extremely rare in urogenital organs, this tumor must be included in the differential diagnosis when we encounter urogenital tumors consisting of mesenchymal elements.

Immunoblot Analysis of CD34 Expression in Histologically Diverse Neoplasms

CD34 is a heavily glycosylated transmembrane protein of approximately 110 kd whose function is essentially uncharacterized. First identified in a myeloid leukemia cell line, immunohistological reactivity with anti-CD34 antibodies is also encountered in a histologically diverse subset of nonhematolymphoid neoplasms including angiosarcoma, solitary fibrous tumors, epithelioid sarcomas, spindle cell lipomas, dermatofibrosarcoma protuberans, and myofibroblastomas. Immunohistological reactivity for CD34 in hematopoietic stem cells and endothelial cells has been shown to correspond to the expression of the CD34 protein. With the exception of gastrointestinal stromal tumors, CD34 protein expression has not been investigated in other CD34 immunohistologically reactive nonhematolymphoid neoplasms. We undertook this study to examine whether the observed reactivity for anti-CD34 antibodies in apparently unrelated tumors is due to the expression of the same protein or whether shared epitopes elaborated by other proteins could account for this reactivity. Immunoblot analyses with anti-CD34 antibodies of six different CD34 immunohistologically reactive lesions show the same approximately 110-kd molecular weight protein. In addition, two cases of dermatofibrosarcoma protuberans show double bands at approximately 110 kd. Laser-capture microdissection of CD34 immunohistologically reactive epithelioid sarcoma and nonreactive epidermal cells illustrates that this reactivity is specific to tumor cells. These results show that the observed immunohistological reactivity with anti-CD34 antibodies is due to the expression of the CD34 protein and not to shared epitopes on unrelated proteins.

Adenomatoid Tumors of the Female Genital Tract: Immunohistochemical Study of CD34 and Factor XIIIa in Eight Cases

Adenonlatoid tumors (ATs) are benign lesions usually arising within the muscularis of the fallopian tube and uterus. Mesothelial differentiation has been demonstrated in ultrastructural and mucin histochemical studies. CD34+ dendritic interstitial cells are putative multipotential precursor cells present in most mesenchyme. Factor XIIIa+ histiocytes are also present in most connective tissue and are increased in tissues undergoing stromal remodeling. To filsther characterize the morphogenesis of AT, we examined 8 female genital ATs for the presence of dendritic fibroblasts that express the human progenitor cell antigen CD34 and for dendritic stromal histiocytes that express coagulation factor XIIIa (FXIIIa). We also studied expression of cytokeratin AEllAE3, tnuscle specific actin HHF35, and endothelial markers CD3 1 and von Willebrand factor. The normal myometrium and myosalpinx consists of actin+ myocytes richly invested with perimyseal CD34+ dendritic fibroblasts, vessels, and scattered small FXIIIa+ histiocytes. Submesothelial fibroblasts are also CD34+. Normal surface mesotheliurn is CD34 negative and keratin+. ATs have cytokeratin+ glands and vacuolated, plexiform, or cord-like structures in a collagenous stroma. In 6 AT, single or small clusters of mesothelium-like acini expressed CD34; however most AT acini were CD34 negative. Some AT glands were partly lined by spindled CD34+ fibroblast-like cells. CD3 1 and anti-von Willebrand factor stained only vessels. Some AT had intraluminal plump FXIIIa+ histiocytes and FXIIIa+ dendritic cells were numerous in the collagenous stroma of some AT. Though the precise biological significance of the data remain speculative, our observations, taken with biochemical data on CD34 and FXIIIa, are consistent with the notion that multipotential CD34+ fibroblast-like interstitial cells in mullerian mesenchyme can undergo mesothelial differentiation to form AT and that FXIIIa+ stromal histiocytes

隆起性皮膚線維肉腫 隆起性皮膚線維肉腫 当科で経験した７例の報告

We report the clinico-pathological features of 7 cases of dermatofibrosarcoma protuberans. The tumor size were from 1.0 to 27cm in diameter. Local recurrence was seen in two cases under the follow up period of 4 months to 22 years. Histologicaly, the tumors of all cases were composed of spindle-shaped cells, and arranged in a storiform pattern. Immunoperoxydase staining with anti-CD34 (human progenitor cell antigen) and anti-factor XIIIa antibodies showed that CD34 was positive and XIIIa was negative in all cases. Clinically, early diagnosis and wide surgical excision are considered to be important to evade recurrence.

Fibrohistiocytic differentiation in subcutaneous fatty tumors. Study of spindle cell, pleomorphic, myxoid, and atypical lipoma and dedifferentiated liposarcoma cases composed in part of CD34+ fibroblasts and FXIIIa+ histiocytes.

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.

Angiosarcoma of the Bladder After Therapeutic Irradiation for Prostate Cancer

No AccessJournal of UrologyClinical Urology: Case Report1 Apr 1997Angiosarcoma of the Bladder After Therapeutic Irradiation for Prostate Cancer Joseph D. Navon, Mariam Rahimzadeh, Alan K. Wong, Philip M. Carpenter, and Thomas E. Ahlering Joseph D. NavonJoseph D. Navon More articles by this author , Mariam RahimzadehMariam Rahimzadeh More articles by this author , Alan K. WongAlan K. Wong More articles by this author , Philip M. CarpenterPhilip M. Carpenter More articles by this author , and Thomas E. AhleringThomas E. Ahlering More articles by this author View All Author Informationhttps://doi.org/10.1016/S0022-5347(01)64980-2AboutFull TextPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail "Angiosarcoma of the Bladder After Therapeutic Irradiation for Prostate Cancer." The Journal of Urology, 157(4), pp. 1359–1360 References 1 : Vaginal and bladder angiosarcoma after therapeutic irradiation. South. Med. J.1989; 82: 1434. Google Scholar 2 : Angiosarcoma of the bladder: a case report with regard to histologic and immunohistochemical findings. Eur. Urol.1991; 20: 161. Google Scholar 3 : Post irradiation angiosarcoma of the vaginal vault. Arch. Path. Lab. Med.1991; 115: 527. Google Scholar 4 : The human hematopoietic progenitor cell antigen (CD34) in vascular neoplasia. Amer. J. Clin. Path.1991; 96: 25. Google Scholar From the Departments of Surgery (Division of Urology) and Pathology, University of California, Irvine Medical Center, Orange, California© 1997 by American Urological Association, Inc.FiguresReferencesRelatedDetails Volume 157Issue 4April 1997Page: 1359-1360 Advertisement Copyright & Permissions© 1997 by American Urological Association, Inc.MetricsAuthor Information Joseph D. Navon More articles by this author Mariam Rahimzadeh More articles by this author Alan K. Wong More articles by this author Philip M. Carpenter More articles by this author Thomas E. Ahlering More articles by this author Expand All Advertisement PDF downloadLoading ...

Immunoreactivity for the human hematopoietic progenitor cell antigen (CD34) in lipomatous tumors.

The human hematopoietic progenitor cell antigen (CD34) recently was shown to react with a variety of nonhematopoietic tissues and their tumors, including vascular endothelium, dendritic interstitial fibroblastic cells, and endoneurial cells as well as with the neoplastic cells in a variety of mesenchymal neoplasms of unknown etiology, such as Kaposi's sarcoma, dermatofibrosarcoma protuberans, epithelioid sarcoma, gastrointestinal stromal tumors, and solitary fibrous tumors. Additionally, it has been claimed that normal adipocytes may also react with this antibody. We studied a series of 90 lipomatous lesions to examine the pattern of immunoreactivity of the CD34 antigen in adipose tissue neoplasms. The study included 14 lipomas, 19 angiolipomas, 4 atypical lipomas, 18 spindle cell lipomas, 3 renal angiomyolipomas, 1 intramuscular lipoma, and 31 liposarcomas. Immunostains identified a network of CD34+ spindle cells admixed with the adipose tissue elements in all cases of lipoma, angiolipoma, angiomyolipoma, intramuscular lipoma, and well-differentiated lipoma-like liposarcoma. Additionally, the spindle cell component in all cases of spindle cell lipoma were strongly positive for this antigen. Atypical, stellate spindle cells and multinucleated "floret" cells in all cases of atypical lipoma as well as in six of 12 cases of well-differentiated lipoma-like liposarcoma of deep soft tissue were also positive for CD34. Scattered spindle cells in all cases of myxoid liposarcoma and in one case of round cell liposarcoma, as well as the sarcomatous component in one case of "dedifferentiated" liposarcoma, were strongly positive for this antigen. The round cells in myxoid liposarcoma and round cell liposarcoma, the signet-ring and multivacuolated lipoblasts in well-differentiated liposarcoma, and the pleomorphic atypical cells in pleomorphic liposarcoma were uniformly negative. The results of this study appear to indicate that lipomatous tumors may harbor a population of CD34+ interstitial dendritic spindle cells. Overgrowth or clonal expansion of this dendritic cell subpopulation may account for the development of spindle cell lipomas and for the spindle cell component in some cases of "dedifferentiated" liposarcoma.

DERMATOPATHOLOGIC ADVANCES IN CLINICAL RESEARCH: The Expression of Antibody to CD34 in Mucocutaneous Lesions

The human progenitor cell antigen, CD34, is selectively expressed in most hematopoietic colony-forming cells from normal human bone marrow, and in a significant proportion of acute leukemias. Within the dermis, CD34 is normally expressed by endothelial cells, dendritic cells, and the spindle-shaped cells around adnexal structures. Benign and malignant vascular lesions, adnexal tumors differentiating toward the external root sheath (trichilemmomas and pilar tumors), specific benign soft tissue tumors (spindle cell lipoma and solitary fibrous tumors), and many of the gastrointestinal stromal tumors uniformly express CD34 antigen. CD34 expression is also often present in benign tumors of neural origin; however, it is less consistently present in malignant peripheral nerve sheath tumors.

Mammary fibroadenoma and some phyllodes tumour stroma are composed of CD34+ fibroblasts and factor XIIIa+ dendrophages.

Fibroadenomas and mammary phyllodes tumour arise by proliferation of mammary stroma and epithelial elements. However, it is the stromal element that determines the biology of these biphasic tumours. Normal mammary stroma, like most collagenous connective tissue, contains resident populations of CD34+ dendritic interstitial cells and scattered factor XIIIa+ collagen-associated dendrophages. Actin+myofibroblasts are usually absent from mammary stroma in non-disease states. To determine whether CD34+ and factor XIIIa+ cells proliferate in fibroadenomas and phyllodes tumours, and to study myofibroblastic differentiation in these lesions, we examined 19 fibroadenomas in 14 patients along with five low grade and two high grade phyllodes tumours. We employed antibodies against the human progenitor cell antigen CD34, coagulation factor XIIIa and HHF-35 actin. In three fibroadenomas and two phyllodes tumours, we used Ki-67 antigen to study cell proliferation and oestrogen and progesterone receptors to study possible hormonal influence on stromal cells. In all fibroadenomas, CD34 strongly stained interlobular, pericanalicular and intracanalicular fibroblasts with collagenous and/or myxoid features. Four low grade phyllodes tumours also had CD34+ fibroblasts as did one high grade tumour. Actin reactivity varied and was most pronounced in six fibroadenomas resembling the so-called cellular variant, while seven regular fibroadenomas had no actin+stromal cells and six had only focal and weak actin+stromal cells. Factor XIIIa+ cells were prominently admixed in the stroma of all tumours studied comprising from 5% to 20% in fibroadenomas and, focally, up to 50% in phyllodes tumours. Oestrogen and progesterone receptors were expressed only in glandular elements. Ki-67 index in stromal cells was 1% to 3% in fibroadenoma, 10% to 20% in low grade, and 20% to 40% in high grade phyllodes tumour. We conclude that fibroadenomas and some phyllodes tumours are composed of CD34+ fibroblasts that show varying myxoid, collagenous or myofibroblastic differentiation. The fibroblasts are accompanied by a subset of dendritic histiocytes that express factor XIIIa. Fibroadenoma variants show prominent collagenous actin+myofibroblastic differentiation of CD34+ stromal cells, sometimes with a gradient of CD34 down-regulation. Fine-needle or limited stereotactic core biopsy of these biphasic tumours, if they yield only stromal cells, must be distinguished from other CD34+ stromal tumours. Increased factor XIIIa+ dendrophage populations were seen in phyllodes tumours, especially in two high grade tumours that had malignant fibrous histiocytoma-like features, suggesting clonal evolution toward the fibrohistiocytic final pathway. Further study of CD34 and factor XIIIa+ mammary stromal cells in larger numbers of phyllodes tumours might ascertain whether increasing factor XIIIa reactivity correlates with differentiation and increased tumour aggressiveness.

Endothelial area as a prognostic indicator for invasive breast carcinoma

BACKGROUND Vascular enumeration using antibodies to Factor VIII has been reported to be an independent prognostic indicator of invasive breast carcinoma. METHODS To eliminate potential subjectivity in distinguishing between individual vessels, especially in areas of tangled capillaries, total endothelial area (EA) was assessed using a Samba 4000 image analyzer. One hundred seventy-eight invasive breast carcinomas (Stage 1 and 2, mean follow-up: 71 months) were immunostained for the presence of CD34, the human hematopoietic progenitor cell antigen also present in endothelium, and EA was quantitated within 5 adjacent 20× fields (0.74 mm2). Additionally, these same vessels were manually counted from the image analyzer. Manual counts were also made from a photomicrograph representative of a single 10× field (1.06 mm2). RESULTS High grade carcinomas contained greater endothelial area than low grade carcinomas (P = 0.0001). Endothelial area was prognostically significant (P = 0.004) in univariate analysis of disease-free survival (DFS) and overall survival (OS), as were stage of disease, tumor size, and combined histologic grade (P;cc 0.024). Manual vessel counts from the monitor were significant for OS only. Manual vessel counts from photomicrographs showed no statistically significant association with DFS or OS. In multivariate analysis, EA, but not vessel enumeration, remained as an independent predictor for OS (lymph node negative patients only, n = 87) and for DFS (lymph node positive patients only, n = 91). For the entire group of patients (lymph node negative and lymph node positive) independent predictors of DFS and OS were tumor grade and size (P;cc 0.006). CONCLUSIONS Of the three methods used to evaluate tumor angiogenesis, total endothelial area, as objectively evaluated by image analysis, was the only independent prognostic indicator for OS for patients with lymph node negative invasive breast carcinoma. Cancer 1996;77:2077-85.

Decreased Expression of the Human Progenitor Cell Antigen (CD34) in Morphea

Morphea is an idiopathic disorder the hallmark of which is fibrosis of the skin. The regulatory factors resulting in the increased collagen production have not been determined. Within the dermis there are dendritic cells with possible immunological functions that express either the human progenitor cell antigen (CD34) or factor XIIIa. Immunohistochemical stains for factor XIIIa, CD34, S100, proliferating nuclear cell antigen, and vimentin were performed on 26 skin biopsies from patients with morphea and 11 biopsies from normal skin. A decreased number of CD34-expressing cells was seen in the affected skin from morphea patients, while there was an increased number of cells expressing factor XIIIa and vimentin. We hypothesize that CD34-positive dendritic cells may have a regulatory role in collagen synthesis and that lack of CD34 expression can be used as a marker for morphea.

Solitary fibrous tumor. Consistent CD34 immunoreactivity and occurrence in the orbit.

The distinction of solitary fibrous tumors (SFTs) from histologically similar neoplasms relies heavily on a characteristic microscopic appearance. No discriminating ultrastructural or immunohistochemical features are known. We evaluated 22 SFTs and 118 other tumors often considered in the differential diagnosis for immunoreactivity using a monoclonal antibody directed against the human hematopoietic progenitor cell antigen, CD34. All the SFTs (22 of 22, 100%) demonstrated strong CD34 immunoreactivity, irrespective of tumor site and histologic grade. Strong and generalized CD34 positivity was also found in most dermatofibrosarcoma protuberans (11 of 12, 92%) and occasional smooth-muscle tumors (leiomyomas 2 of 11, 18%; leiomyosarcomas 2 of 11, 18%). Variable numbers of CD34 positive cells were present in all neurofibromas (9 of 9, 100%) and focally present in most schwannomas (8 of 9, 89%). Some of the hemangiopericytomas (7 of 16, 44%) exhibited CD34 immunoreactivity, however, generally with weak intensity and patchy distribution. CD34 immunoreactivity was not observed in mesotheliomas (0 of 20, 0%), synovial sarcomas (0 of 13, 0%), fibrosarcomas (0 of 12, 0%), or spindle-cell thymomas (0 of 5, 0%). We conclude that CD34 immunoreactivity is a sensitive marker for SFT and, in conjunction with an appropriate immunohistochemical panel, may be useful in discriminating SFTs from other histologically similar neoplasms. The observation that some mesenchymal stromal cells and SFTs share a CD34-positive immunophenotype suggests a histogenetic relationship. The inclusion in this study of two cases of SFTs arising in the orbit establishes another site of origin for this tumor and provides further support for a mesenchymal histogenesis.

QBEND/10 (anti-CD34 antibody) in external root sheath cells and follicular tumors.

The human hematopoietic progenitor cell antigen (CD34) is a cell surface protein expressed by human hematopoietic progenitor cells, vascular endothelium, and many mesenchymal tumors. Sections from six samples of normal skin and from 41 epithelial tumors of the skin were studied. Immunostaining of epithelial cells from the external root sheath below the attachment of the arrector pili muscle and above the matrix cells was noted in normal samples. Tumors derived from or differentiated toward cells of the outer sheath, especially trichilemmomas, were immunostained with QBEND/10 (anti-CD34 antibody), whereas other epithelial tumors studied were negative. CD34 could serve as a marker of outer sheath cell derivation and may well be of value in the distinction between trichilemmomas and other lesions with similar histopathological features.