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The laminated inclusions in the rough endoplasmic reticulum (RER) are peculiar structures seen only in some cases of chondrocytes of pseudoachondroplasia. These ultrastructurally unique organelles have not yet been reported in inflammatory malignant fibrous histiocytoma (MFH). We describe an omental mass showing unique laminated inclusions in the RER in a young man with intra-abdominal inflammatory MFH. The most striking ultrastructural feature was a dilated RER containing a fine granular substance and a more electron-dense material exhibiting an onion skin-like lamellated or maze-like pattern, mimicking that of so-called laminated inclusions. These lamellated inclusions occupied most of the cytoplasm of the tumor cells. We speculate that the ultrastructural finding of the laminated RER inclusion is not specific for cartilage cells, but may represent abnormal accumulation of some kind of glycoprotein material or matrix protein. This granular material may undergo organization to form a peculiar laminated structure, probably due to a metabolic or fixation process. Further study is needed to elucidate the nature of this material.

To discuss the dental origin of odontogenic myxoma and to provide further information for the differential diagnosis between this tumor and myxoid malignant fibrous histiocytoma (MFH) which occasionally occurs in jaw bones, the contents of glycosaminoglycans (GAGs) and proteoglycans (PGs) in the mucosubstances of 15 odontogenic myxomas, 5 myxoid MFH and 3 human fetal tooth germs in the bell stage of development were characterized using histochemical and immunohistochemical methods. Histochemical staining of hyaluronic acid (HA) was undertaken using biotinylated HA binding protein (B-HABP), and immunohistochemical detection was done using a panel of antibodies against chondroitin 6-sulfate (CS-6), chondroitin 4-sulfate (CS-4), dermatan sulfate (DS), keratan sulfate (KS), heparan sulfate (HS), aggrecan, PG-M/versican, decorin and biglycan. In odontogenic myxoma, CS-6, HA and PG-M/versican were observed in the myxomatous matrix of all cases, while KS and HS were seen in none. As for CS-4, DS, aggrecan, decorin and biglycan, only irregular and mild stainings were shown. Consistent and strong positive straining for CS-6, HA and PG-M/versican were seen in dental papilla and provided evidence supporting the origin of this tumor from dental papilla. Except for the constant staining for HA, the myxoid matrix was rarely stained for most GAGs and PGs in myxoid MFH. Immunodetection of CS-6 and PG-M/version with the use of monoclonal antibodies 3-B-3 and 2-B-1 is therefore recommended as a useful tool in differentiating odontogenic myoma from myxoid MFH.

CD34 and factor XIIIa (FXIIIa) antibodies delineate subsets of embryonic dendritic stromal stem cells that persist in adult mesenchyme. CD34 stains interstitial and adventitial dendritic cells that may function as multipotential precursor cells. FXIIIa+ dendrophages are tissue histiocytes active in tissue repair. Angiomatoid malignant fibrous histiocytoma (AMFH) is an enigmatic fibrohistiocytic tumor with limited vascular features. We examined an unusual soft tissue tumor from the nasolabial subcutis of a 57 year old man that showed histologic features of AMFH. Most of the tumor cells expressed CD34. 10-30% of the tumor cells were FXIIIa+ dendrophages. Sinusoidal areas were largely composed of FXIIIa+ cells that also expressed HLA-DR and CD68 suggesting macrophage differentiation. CD31 and Factor VIII antigen highlighted capillaries and single cells among the CD34+ tumor cells. The vessels had actin+ myopericytes and there were single actin+ tumor cells. Electron microscopy showed primitive dendritic cells and fewer histiocyte-like cells. The Ki 67 index was 15% including both FXIIIa+ and CD34+ cells. The patient is disease free three years after wide excision. We conclude that this AMFH-like neoplasm is a fibrohistiocytic tumor in which CD34+ fibroblast-like precursors and FXIIIa+ tissue dendrophages combine to build both sinusoidal tissue with endothelial and macrophage elements as well as capillary vascular tissue that is invested with myopericytes. Study of additional AMFH lesions from this standpoint is desirable.

Immunostaining of the cell cycle-associated Ki-67 antigen was studied on routinely formalin-fixed and paraffin-embedded tissue sections, using the Ki-67-specific monoclonal antibody MIB-1. Immunomorphological analysis of the Ki-67 immunostaining pattern was carried out following tissue pre-treatments including combinations of microwave heating and trypsinization, as well as of ribonuclease and deoxyribonuclease pre-digestion of the sections. The nucleolar Ki-67 immunostaining after slide pre-treatment by microwave heating followed by trypsinization was reduced only by ribonuclease pre-digestion, if this latter was used before heating. Ki-67 immunostaining was not significantly reduced by deoxyribonuclease treatment. We conclude that Ki-67, located in the nucleoli, may be associated there with nucleolar RNA.

A typical case of plexiform fibrohistiocytic tumor (Enzinger and Zhang) occurring in the skin and subcutis of the abdominal wall in a 7-year-old girl is reported. Preoperative fine-needle aspiration cytology revealed a benign lesion with fibroblastic-histiocytic features which also contained bi- and multinucleated giant cells. The surgical specimen showed a tumor with multiple small nodules within fibrous septa; these nodules were composed of spindle cells and epithelioid cells and contained scattered multinucleated osteoclast-like cells. The tumor cells showed ultrastructural and immunohistochemical features of myofibroblasts and histiocyte-like cells. Thus, there was an abundance of lysosomes, prominent filopodia and bundles of thin cytofilaments along the cytoplasmic border, as well as immunoreactivity for alpha-smooth-muscle-specific actin, alpha-1-antitrypsin and alpha-1-antichymotrypsin. Ultrastructurally there were tumor cells exhibiting features of histiocytes which also contained bundles of actin of smooth muscle type. The presented case of plexiform fibrohistiocytic tumor appears to be composed of a rather peculiar cell form, somewhere between myofibroblasts and histiocytes.

Nine cases of malignant fibrous histiocytomas (MFH) were examined immunohistochemically in frozen sections with six different monoclonal antibodies to histiomonocytic and related cells (EBM11, HAM-56, KB90, antibodies to dendritic reticulum cells, HLADR and LCA). Ten other soft tissue sarcomas, two desmoid tumors, twelve carcinomas, three seminomas and four lymphomas were studied for comparison. All cases of MFH showed positivity for histiomonocytic cell antigens. In six cases, the positive cells could be clearly interpreted to be infiltrating non-neoplastic cells. However, immunoreactivity for multiple histiocytic markers (EBM11, HAM-56, KB90, HLADR) was seen in tumor cells in three cases of MFH. In one of these cases, the positivity could be verified with KP1, an antibody to histiomonocytic cells applied in formalin fixed and paraffin embedded tissue. None of the tumors was positive with the antibody to dendritic reticulum cells or LCA. In the series of non-histiocytic tumors, no cases showed widespread positivity for multiple histiocytic markers. Our results suggest that in relation to true histiomonocytic differentiation MFH might be a heterogeneous group of tumors. The widespread immunoreactivity for multiple histiocytic markers in some cases may indicate a true histiomonocytic differentiation in some MFHs.