Myoepitheliomas and Myoepithelial Adenomas of Salivary Gland Origin

Lactoferrin in human tumours: immunohistochemical investigations during more than 25 years

Lactoferrin (LF) is an iron-binding glycoprotein of the transferrin family, today known to have multifunctional physiological activities. In humans, under normal conditions, LF has been found in blood, mucosal secretions, gastrointestinal fluids, urine and mostly in milk and colostrum. The first pioneering immunohistochemical report about LF distribution in human tissues dated in 1978; successively, many studies have been performed to analyze the LF immunohistochemical pattern in different normal and neoplastic tissues. In this review, we present data from literature concerning the evidence of LF in tumors together with those by us obtained during more than 25 years; the immunohistochemical applications to human neoplastic tissues have been done to investigate the LF pathogenetic role as well as its activity in cancer. After a systematic analysis of LF immunoreactivity in different human districts, a possible explanation for its presence and function has been modulated for each site or tissue, according to experimental evidences obtained either by in vivo as well as by in vitro studies.

A distinctive novel epitheliomesenchymal biphasic tumor of the stomach in young adults ("gastroblastoma"): a series of 3 cases

This report describes 3 cases of a distinctive, hitherto unreported gastric epitheliomesenchymal biphasic tumor that differs from other biphasic tumors of the stomach and elsewhere: carcinosarcoma, biphasic synovial sarcoma, teratoma, and mixed tumor. The tumors occurred in young adults, 2 males and 1 female, of ages 19, 27, and 30 years. Two tumors were located in the greater curvature in the gastric body and one in the antrum. The tumors measured 5, 6, and 15 cm in maximum diameter, and their mitotic rates were 0, 4, and 30 mitoses per 50HPF. There were 2 components: uniform oval or spindled cells in diffuse sheets, and clusters or cords of epithelial cells occasionally forming glandular structures with small lumens. The epithelial elements were positive for keratin cocktail AE1/AE3, keratin 18, and partly for keratin 7, but were negative for keratins 5/6, 20 and epithelial membrane antigen. The spindle cells were positive for vimentin and CD10. All components were negative for CD34, CD99, estrogen receptor, KIT, smooth muscle actin, desmin S100 protein, p63, calretinin, chromogranin, synaptophysin, CDX2, and thyroid transcription factor 1. In situ hybridization for SS18 rearrangement was negative in all cases separating this tumor from synovial sarcoma. All 3 patients were alive after follow-up of 3.5, 5, and 14 years. Because these tumors have some resemblance to blastomas of other organs, we propose the term "gastroblastoma" for this distinctive, at least low-grade malignant epitheliomesenchymal tumor of the stomach.

Interlobular excretory ducts of mammalian salivary glands: structural and histochemical review

In the major salivary glands of mammals, excretory ducts (EDs) succeed striated ducts. They are for the most part interlobular in position, although their proximal portions sometimes are on the periphery of a lobule, where they occasionally retain some of the structural features of striated ducts. Based on a survey of a broad range of mammalian species and glands, the predominant tissue type that composes EDs is pseudostratified epithelium. In some species, there is a progression of epithelial types: the proximal EDs are composed of simple cuboidal or columnar epithelium that, in the excurrent direction, usually gives way to the pseudostratified variety. Secretory granules are visible in the apical cytoplasm of the principal cells of the EDs of only a few species, but histochemistry has shown the presence of a variety of glycoproteins in these cells in a spectrum of species. Moreover, the latter methodology has revealed the presence of a variety of oxidative, acid hydrolytic, and transport enzymes in the EDs, showing that, rather than simply acting as a conduit for saliva, these ducts play a metabolically active role in gland function. It is difficult to describe a "typical" mammalian ED because it can vary along its length and interspecific variation does not follow a phylogenetic pattern. Moreover, in contrast to intercalated and striated ducts, ED cellular features do not exhibit a relationship to diet.

Immunocytochemistry of myoepithelial cells in the salivary glands

MECs are distributed on the basal aspect of the intercalated duct and acinus of human and rat salivary glands. However, they do not occur in the acinus of rat parotid glands, and sometimes occur in the striated duct of human salivary glands. MECs, as the name implies, have structural features of both epithelial and smooth muscle cells. They contract by autonomic nervous stimulation, and are thought to assist the secretion by compressing and/or reinforcing the underlying parenchyma. MECs can be best observed by immunocytochemistry. There are three types of immunocytochemical markers of MECs in salivary glands. The first type includes smooth muscle protein markers such as alpha-SMA, SMMHC, h-caldesmon and basic calponin, and these are expressed by MECs and the mesenchymal vasculature. The second type is expressed by MECs and the duct cells and includes keratins 14, 5 and 17, alpha 1 beta 1 integrin, and metallothionein. Vimentin is the third type and, in addition to MECs, is expressed by the mesenchymal cells and some duct cells. The same three types of markers are used for studying the developing gland. Development of MECs starts after the establishment of an extensively branched system of cellular cords each of which terminates as a spherical cell mass, a terminal bud. The pluripotent stem cell generates the acinar progenitor in the terminal bud and the ductal progenitor in the cellular cord. The acinar progenitor differentiates into MECs, acinar cells and intercalated duct cells, whereas the ductal progenitor differentiates into the striated and excretory duct cells. Both in the terminal bud and in the cellular cord, the immediate precursors of all types of the epithelial cells appear to express vimentin. The first identifiable MECs are seen at the periphery of the terminal bud or the immature acinus (the direct progeny of the terminal bud) as somewhat flattened cells with a single cilium projecting toward them. They express vimentin and later alpha-SMA and basic calponin. At the next developmental stage, MECs acquire cytoplasmic microfilaments and plasmalemmal caveolae but not as much as in the mature cell. They express SMMHC and, inconsistently, K14. This protein is consistently expressed in the mature cell. K14 is expressed by duct cells, and vimentin is expressed by both mesenchymal and epithelial cells. After development, the acinar progenitor and the ductal progenitor appear to reside in the acinus/intercalated duct and the larger ducts, respectively, and to contribute to the tissue homeostasis. Under unusual conditions such as massive parenchymal destruction, the acinar progenitor contributes to the maintenance of the larger ducts that result in the occurrence of striated ducts with MECs. The acinar progenitor is the origin of salivary gland tumors containing MECs. MECs in salivary gland tumors are best identified by immunocytochemistry for alpha-SMA. There are significant numbers of cells related to luminal tumor cells in the non-luminal tumor cells that have been believed to be neoplastic MECs.

Pleomorphic adenoma with nuclear palisading arrangement of modified myoepithelial cells: histopathologic and immunohistochemical study

Pleomorphic adenomas with a nuclear palisading arrangement of spindle-shaped modified myoepithelial cells (MMCs), suggesting the appearance of palisading leiomyoma or Antoni's A type of neurilemmoma, are quite rare, and its cytologic nature has been poorly understood. This paper reports histologic and immunohistochemical findings of palisading MMCs in two cases of pleomorphic adenoma. Histologically, foci of spindle-shaped MMCs with nuclei in a palisading arrangement were scattered in the myxoid areas. Near the large foci of spindle-shaped MMCs with nuclear palisading arrangements, tiny foci of spindle-shaped MMCs forming nuclear palisading or rosette-like arrangements were seen. Such nuclear palisading arrangements of MMCs were suggestive of differentiation or transformation of MMCs into cells that were more smooth muscle in nature, supported by occasional existence of palisading leiomyoma in the myometrium and gastrointestinal tract. However, immunohistochemical findings of palisading MMCs in pleomorphic adenoma were similar to those of non-palisading MMCs, and showed no evidence of smooth muscle differentiation; neither palisading nor non-palisading MMCs in pleomorphic adenoma expressed desmin, muscle specific actin (HHF-35), alpha smooth muscle actin, or myoglobin. The biologic significance and formative mechanism of nuclear palisading arrangement of MMCs in pleomorphic adenoma could not be determined in the present study. However, if the MMCs with nuclear palisading arrangements in pleomorphic adenoma, presented here, are aspirated for cytologic diagnosis or are included in a small biopsy specimen, the correct diagnosis of pleomorphic adenoma may be confused by a suspicion of myogenic or neurogenic tumor.

Immunocytochemical identification of different cell types in bovine nasolabial glands with particular emphasis on cytoskeletal protein expression

Nasolabial glands are serous glands forming a thick subcutaneous layer in the bovine muzzle. In order to identify the different epithelial cell types, both immunofluorescent and immunoperoxidase techniques were employed on frozen and fixed sections using monoclonal antibodies to cytoskeletal proteins and S-100. Actin was also detected with phalloidin. The results show that four cell types can be identified on the ground of the different composition of the cytoskeletal filaments: acinar, basket, luminal duct and basal duct cells. Acinar, luminal duct cells and basal duct cells express different patterns of cytokeratins, as shown by the 12 anti-cytokeratin monoclonal antibodies used, and both basket cells and the basal cells of intercalated ducts are also reactive to phalloidin and anti-alpha-smooth muscle actin monoclonal antibody. The presence of actin supports the conclusion that basal duct cells are also contractile elements, i.e. myoepithelial cells. Vimentin, glial fibrillary acidic protein (GFAP), and S-100, molecules considered to be markers of myoepithelial cells by many AA., were not found. The intermediate filaments of the duct epithelium appear more complex and heterogeneous in comparison with those present in the acinar cells.

Identification of an alternative form of human lactoferrin mRNA that is expressed differentially in normal tissues and tumor-derived cell lines

Lactoferrin (LF), traditionally known as an iron-binding protein present in high concentrations in milk and various secretions, has emerged as a multifunctional protein involved in many aspects of the host defense against infection. Recently, LF has been shown to inhibit the growth of solid tumors and reduce experimental metastasis in mice, suggesting that LF also may play a role in the defense against tumorigenesis. Here we provide the sequence of the cDNA and promoter region, the chromosome assignment, and tissue expression pattern of a novel form of LF mRNA (delta LF). The sequence of delta LF mRNA is nearly identical to that of LF mRNA; however, at the 5' end, we find a novel sequence that replaces the N-terminal signal peptide sequence of LF mRNA. We map the delta LF mRNA to human chromosome 3 and find that both delta LF and LF sequences colocalize to the same cloned 90- to 150-kb genomic DNA fragment. We further show that the delta LF mRNA is the product of alternative splicing of the LF gene and likely is specified by use of an alternative promoter. Although we find delta LF mRNA at various levels in 20 of 20 adult and fetal human tissues, we do not find delta LF mRNA in any of 14 diverse tumor-derived cell lines.

Immunohistochemical evaluation of the Ca(2+)-binding S-100 proteins S-100A1, S-100A2, S-100A4, S-100A6 and S-100B in salivary gland tumors

The Ca(2+)-binding S-100 proteins are involved in the regulation of a number of cellular processes and an altered expression has been reported in several neoplastic tissues. Tissue specimens of normal salivary glands (n = 23), pleomorphic adenomas (n = 60), basal cell adenomas (n = 6), canalicular ademomas (n = 2), myoepitheliomas (n = 2), adenoid cystic carcinomas (n = 26) and adenocarcinomas NOS (n = 11) were evaluated for the expression of S-100A1, S-100A2, A-100A4, S-100A6 and S-100B by using highly specific polyclonal and monoclonal antibodies generated against the recombinant human protein. In normal salivary glands, the ductal cells showed mild to intense immunoreactivity for S-100A1, S-100A2, S-100A4 and S-100A6, while S-100B was observed in nerve fibers in the connective tissue. The normal myoepithelial cells were unreactive. In pleomorphic adenoma, the luminal tumor cells of the duct-like structures showed moderate to intense immunoreactivity for S-100A2, while reactivity for S-100A1, S-100A4 and S-100A6 was relatively weak. The non-luminal cells, also termed neoplastic myoepithelial cells, showed immunoreactivity for S-100B, while tumor cells in the solid, myxoid and chondroid areas were immunoreactive for S-100A1, S-100A4, S-100A6 and S-100B. The non-luminally located tumor cells in basal cell adenomas and canalicular adenomas, and numerous tumor cells in clusters in myoepitheliomas were intensely reactive for S-100A2. In adenoid cystic carcinomas and in adenocarcinomas not otherwise specified, the luminal cells forming the tubular or cribriform structures were markedly positive for S-100A2 and/or S-100A6. Squamous metaplastic cells in salivary tumors showed intense immunoreactivity for S-100A2. The results of the present study suggest that the majority of the tumor cells in salivary neoplasms, despite the most heterogeneous tumor cell differentiation, express S-100 proteins more heterogeneously than the normal glandular ducts. The salivary ducts in normal glands, the luminal tumor cells and squamous metaplastic cells in the neoplastic lesions were intensely immunoreactive for S-100A2 as compared to S-100A1, S-100A4 or S-100A6. In contrast, the non-luminal tumor cells showed a rather heterogeneous expression of the S-100 proteins.

Expression of cytokeratins in Warthin's tumour (adenolymphoma) of parotid glands: specific detection of individual cytokeratin types by monoclonal antibodies

This study evaluated the distribution of cytokeratins detected by monoclonal antibodies directed against individual keratin proteins in normal human salivary glands and epithelial tumour cells of Warthin's tumour arising in parotid glands to determine a more precise mapping of their cellular distribution. The normal salivary ducts showed the presence of cytokeratin 7, 8, 18 and 19 in the intercalated, striated and excretory ducts, the primary keratins of stratified and simple epithelia with a profile very similar to the non-cornified epithelium of the oral mucosa. The basally located cells of salivary gland ducts other than myoepithelial cells were reactive for keratins 7 and 19 suggesting a close similarity in profile of keratin in the basal cells of the oral epithelium. In Warthin's tumour, keratins 7, 8, 18 and 19 were consistently detected in the epithelial cells of the tumour, a profile with a tendency to mimic the same in normal ductal epithelium. The distribution, however, was diverse and a heterogeneity was observed in the basal and luminal cells of Warthin's tumour which differed even in different areas of the same tumour specimen.

Myoepithelioma: definitions and diagnostic criteria

Due to their infrequency and multiplicity of histopathology, myoepitheliomas present difficulties in diagnosis and classification. Cellular varieties can be misdiagnosed as malignancies. Improvements in and clarification of diagnostic criteria are, therefore, required. A key to determining diagnostic criteria for myoepitheliomas is to study cellular morphology, cytoplasmic filament expression, and ultrastructural features of the nonluminal, i.e., neoplastic myoepithelial/basal, tumor cells of pleomorphic adenomas, and apply this information to defining myoepitheliomas. Cytologic and growth patterns of nonluminal cells in pleomorphic adenomas, including plasma-cytoid cells, are reflected in myoepitheliomas. Results also indicate that muscle-specific actin and myofilaments are expressed only in a proportion of cases, and generally in not more than 60-70% of nonluminal cells in pleomorphic adenoma; this also applies to benign and malignant myoepitheliomas. The absence of these markers does not exclude a diagnosis of myoepithelioma. Vimentin and glial acidic fibrillary protein, however, are strongly and diffusely expressed in the majority of pleomorphic adenomas and myoepitheliomas and are more reliable markers for these tumors than muscle-specific actin. Like so many other salivary gland tumors, myoepitheliomas present an equally complex histomorphology and variable expression of antigenic markers, only some of which are associated with myoepithelial and basal cells of the acini and ducts of the normal salivary gland.

Benign myoepithelioma of the salivary glands: a true entity?

Myoepithelioma is a rare neoplasm of the salivary glands which is now recognized as an individual entity in the revised WHO classification. In this study, eleven benign tumours are presented. Most patients gave a history of a slowly enlarging mass, which was cured by surgical excision. However, one case recurred several times over 50 years, and another still has residual tumour and removal is not possible. The histological appearances included solid, myxoid and reticular growth patterns, composed predominantly of spindle shaped or plasmacytoid (hyaline) cells. Many of the tumours also contained occasional small ducts. All 11 tumours were positive for S-100 protein, variable reactions being seen for various other antigens--keratins, human milk fat globulin, carcinoembryonic antigen, alpha smooth muscle actin and vimentin. It is probable that myoepithelioma constitutes one end of a biological spectrum which also includes pleomorphic adenoma and some (non-membranous) basal cell adenomas. In practice, however, we still advocate retention of myoepithelioma as a separate diagnostic category, on the grounds that it has a range of distinctive microscopic appearances and poses its own unique problems in correct identification.

Immunohistochemical evaluation of bone morphogenetic protein (BMP) in mixed tumor of skin

Immunohistochemical reaction of bone morphogenetic protein (BMP) was assessed in 19 cases of skin mixed tumor and 5 cases of skin appendage tumors by using monoclonal antibody raised against BMP. All cases of skin mixed tumor showed positive staining for BMP in modified myoepithelial cells located at the periphery of tubulo-ductal or solid structures, and in plasmacytoid or tumor cells in hyalinous structures. Chondroidally changed cells also showed a strong BMP immunoreactivity. Tumors originating from sweat glands were devoid of BMP immunoreactivity. It is concluded that BMP is synthesized and produced in modified or transformed myoepithelial cells in skin mixed tumor and participates in the process of chondroid changes in the tumor.

Histogenesis and possible mechanism of chondroid changes in mixed tumour of the skin: immunohistochemical evaluation of bone morphogenetic protein, glycosaminoglycans, keratin, vimentin and neuronal markers

The distribution of immunoreactivity of bone morphogenetic protein (BMP), the glycosaminoglycans chondroitin 4-sulphate (C4SPG), chondroitin 6-sulphate (C6SPG), dermatan sulphate (DSPG) and keratan sulphate proteoglycans (KSPG), cytokeratin (K8.12), vimentin, glial fibrillary acidic protein (GFAP), actin, desmin, S-100 protein and neuron-specific enolase (NSE) in mixed tumour of the skin was investigated using immunohistochemical methods using monoclonal (MoAb) and polyclonal antibodies (PoAb). A strong BMP immunoreactivity was found characteristically in outer tumour cells of tubuloductal structures and modified myoepithelial cells. Modified myoepithelial cells and chondroidally changed cells showed positive immunoreactivity for C4SPG, C6SPG and DSPG; and KSPG was more pronounced in the modified myoepithelial cells. Vimentin, S-100 protein, GFAP and NSE, but not actin and desmin, were distribute in the outer tumour cells and modified myoepithelial cells in chondroidally changed tissue. Two factors show that chondrogenesis in mixed tumour of the skin is associated with the modified myoepithelial cells through the activity of BMP and biosynthesis of glycosaminoglycans as matrix substance. First, outer or basal tumour cells in mixed tumour of the skin is characterized by the presence of positive immunoreactivity for BMP, KSPG, vimentin, cytokeratin K8.12, S-100 protein, GFAP and NSE, and second, there is a matrix of chondroidally changed tissue containing the reaction products of C4SPG, C6SPG, DSPF and KSPG.

Myoepithelium of salivary glands

In salivary glands and other exocrine organs, there are starfish-shaped cells that lie between the basal lamina and the acinar and ductal cells. These have structural features of both epithelium and smooth muscle cells, and so are called myoepithelial cells. Their functions include contraction when the gland is stimulated to secrete, compressing or reinforcing the underlying parenchymal cells, thus aiding in the expulsion of saliva and preventing damage to the other cells. They also may aid in the propagation of secretory and other stimuli. Their common developmental origin with the basal cells of the larger ducts is displayed in the mature glands by shared structural and immunohistochemical features, but most such basal cells do not have the distinguishing features of myoepithelial cells, such as myofibrils. Although myoepithelial cells can be identified by light microscopy through enzyme histochemistry and special stains and immunohistochemistry for their myofibrils, these techniques can be misleading in salivary gland neoplasms. Thus, the most reliable means of identifying neoplastic myoepithelial cells is with a combination of histochemistry and electron microscopy. The extent to which these cells are derived from undifferentiated stem cells in both normal and neoplastic growth is controversial. The presentation here of transmission electron microscopy (TEM) of well-differentiated myoepithelial cells in mitotic division indicates that stem cells are not necessarily the only source of myoepithelial cells in the later stages of salivary gland development or in neoplasia.

S100 protein is not specific for myoepithelial cells in the canine mammary gland

The distribution of protein S100 in the canine mammary gland was studied, this substance having been described as specific for myoepithelial cells. Two immunohistochemical methods, peroxidase-anti-peroxidase complex (PAP) and alkaline phosphatase-anti-alkaline phosphatase complex (APAAP) were used on frozen sections of normal canine mammary gland. Both the myoepithelial and epithelial cells stained positively with PAP. With APAAP, staining was also seen in the controls, presumably because endogenous alkaline phosphatase was not blocked. As protein S100 was shown to be present both in myoepithelial and epithelial cells of the mammary gland, it was concluded that S100 is not a specific marker for myoepithelial cells.

Benign and malignant neoplasms of myoepithelial cells: cytologic findings

We report two myoepithelial cell neoplasms; a salivary gland tumor was malignant and a breast neoplasm was benign. Both were studied histologically, immunohistochemically, cytologically, and ultrastructurally. The malignant myoepithelioma recurred twice and metastasized to one regional lymph node. This tumor was infiltrative with areas of necrosis and hemorrhage. It was composed of malignant-appearing spindle and plasmacytoid cells. Both types of cells were immunoreactive to muscle specific actin, S-100 protein, cytokeratin, vimentin, and neuron-specific enolase. Ultrastructurally, features of myoepithelial cells were seen. Fine-needle aspirate smears showed spindle and plasmacytoid cells, numerous mitoses, and malignant-appearing nuclei. Spindle-cell adenomyoepithelioma of the breast, a small well-circumscribed firm nodule, featured multiple lobules of spindle cells associated with clear-cell glands at the lobular periphery. Histologically and cytologically, the lesion was cellular but appeared benign. The differential diagnosis of myoepithelial neoplasms is discussed.

Immunohistochemical detection of S-100, S-100 alpha, S-100 beta proteins, glial fibrillary acidic protein, and neuron specific enolase in the prenatal and adult human salivary glands

Developing human fetal salivary glands of gestational age from 10 to 40 weeks (n = 100) and normal adult glands (n = 10) were examined for immunoreactivity to S-100 protein and its subunits S-100 alpha, S-100 beta, glial fibrillary acidic protein (GFAP) and neuron specific enolase (NSE). In the early intermediate developmental stage (19-32 weeks) some acinar basal cells showed immunoreactivity to S-100 protein which rapidly disappeared in the late developmental stage (33-40 weeks). Adult salivary glands were negative for S-100 protein. The S-100 alpha subunit was strongly positive in the glandular ducts and acini of both fetal and adult glands. The S-100 beta, although present in some acini and ductal cells during the late intermediate developmental stage, was rarely seen in the adult glands. GFAP and NSE was positive at the developing salivary epithelium in the early developmental stage (15-18 weeks). The above findings indicated that the developing salivary epithelia showed transient appearance of the neuronal phenotype during active cytodifferentiation stage of glandular acini and ducts. Therefore, after evaluation of normal developmental and neoplastic transformation of the salivary glands a suggestion that neuronal differentiation of ductal reserve cells is responsible for the production of modified myoepithelial cells in both normal developmental salivary gland and neoplastic transformation is made.

An immunohistochemical study of bone morphogenetic protein in pleomorphic adenoma of the salivary gland

Bone morphogenetic protein (BMP) is a potent induction factor for new bone formation including heterotopic chondro-ossification in soft tissues. The immunohistochemical reaction for BMP was studied in 23 cases of pleomorphic adenoma of salivary gland by using a monoclonal antibody produced by hybridoma technique. Positive BMP immunoreactivity was seen in 87% of tumours. Immunohistochemical expression of BMP was observed in modified myoepithelial cells (88% cases), luminal tumour cells of tubulo-ductal structures (78% cases) and chondroid cells in hyaline tissue (22% cases). The authors concluded that the simultaneous presence of glycosaminoglycans as matrix substance with BMP-mediated cellular activity of modified myoepithelial cells in the formation of chondroid structures in pleomorphic adenomas of the salivary glands.

Chondroid syringoma with hyaline cell change

Four cases of chondroid syringoma containing large numbers of hyaline or plasmacytoid cells are described. Three cases occurred in the hand and one in the foot. Hyaline cells are commonly seen in mixed tumours and myoepitheliomas of salivary glands and rarely in chondroid syringomas. The hyaline-cell change in three of the cases initially caused diagnostic difficulties and the possibility of sarcoma was raised in two cases. In addition to the characteristic hyaline cells, the presence of tubulo-glandulo-ductal structures, benign squamous epithelium and myxochondroid stroma aided diagnosis. Immunohistochemically, the hyaline cells exhibited positivity for vimentin, cytokeratin, S-100 protein, carcino-embryonic antigen, focal glial fibrillary acidic protein (3 cases), neuron-specific enolase (3 cases) and focal alpha-smooth muscle actin (2 cases). Occasional cells were Ber EP4 positive (2 cases). In some cells, a striking peripheral ring-like positivity for cytokeratin and S-100 protein was noted. Ultrastructurally, desmosomes, varying numbers of tonofibrils and non-bundling intermediate filaments were seen. Scanty fine filaments with vague focal densities were detected in some cells. Our studies suggest that the hyaline cells represent modified epithelial as well as myoepithelial cells. One of our cases also exhibited collagenous spherulosis.

Keratin and vimentin distribution patterns in the epithelial structures of the canine anal region

The intermediate filament labeling pattern of the epithelial structures of the canine anal region was studied with different polypeptide specific keratin monoclonal antibodies (MoAbs) and with a monoclonal and polyclonal vimentin antibody. The epithelial structures in this region could be discriminated and characterized by differences in their keratin staining pattern. The basal cells in the different epithelial structures showed a similar staining pattern characterized by reactivity with MoAbs staining keratins 5, 8, 14, and 17. Columnar epithelial cells showed a completely different phenotype mostly characterized by reactivity with MoAbs staining keratins 7, 5, 8, 18, and 19. A restricted number of differentiated perianal gland cells showed perinuclear vimentin staining. Myoepithelial cells did not stain for vimentin, but, as other basal cells, were positive for MoAbs staining keratins 5, 8, 14, and 17.

Histopathology of myoepithelial (basocellular) hyperplasias in adenosis and epitheliosis of the breast demonstrated by the reactivity of cytokeratins and S100 protein. An analysis of heterogenic cell proliferations in 90 cases of benign and malignant breast diseases

This study on the different types of epithelial hyperplasia in fibrocystic disease was inspired by the observation of myoepithelial (basocellular) hyperplasia identified by strong expression of S100 protein and a weak reaction with antibodies against cytokeratin (KL1) in cells forming solid and acinar buds. The cells do not contain immunohistochemically detectable actin or desmin. Glandular transformation and proliferation give rise to basocellular circumductal adenosis. Normal breast tissue, 51 cases of fibrocystic disease with mild, florid and atypical hyperplasias, 7 fibroadenomas and 20 cases of carcinoma in situ were studied and a semiquantitative analysis revealed basal buds and adenosis in less than 40% of cases of mild hyperplasia and up to 73% in florid hyperplasia. Epitheliosis is characterized by a heterogeneous cell pattern with cells positive for S100 protein in 30-60%, but in small ducts up to 100% with an immediate connection to the basal cell layer were positive. Carcinoma in situ contained very rare tumour cells positive for S100 protein. The cells expressing S100 protein in terminal ducts, in adenosis and epitheliosis showed only some of the characteristics of myoepithelial cells, since they lack immunoreactivity with antibodies against actin. These basal clear cells are interpreted as transitional or indeterminate cells with features of myoepithelial precursor cells, but with the ability to develop basocellular nodular and glandular hyperplasia in the ductulo-lobular units in cases of adenosis and juvenile fibroadenoma.

The World Health Organization's Histological Classification of Salivary Gland Tumors. A commentary on the second edition

The second edition of the World Health Organization's Histological Classification of Salivary Gland Tumors is more extensive and detailed than the previous edition published 20 years ago. The new edition is based on data regarding newly described tumor entities and the behavior and prognosis of the previously classified tumors. The distinct morphologic features of monomorphic adenomas justify their separation for purposes of identification. Among the carcinomas, various types were distinguished for purposes of recognition, prognosis, and treatment. The term tumor was replaced by carcinoma in the following two entities: acinic cell carcinoma and mucoepidermoid carcinoma. The tumor-like lesions were described in more detail.

Immunohistochemical and ultrastructural correlates of muscle-actin expression in pleomorphic adenomas and myoepitheliomas based on comparison of formalin and methanol fixation

The degree and range of differentiation of the cells referred to as myoepithelial-like in pleomorphic adenomas and the tumour cells of myoepitheliomas are not definitely established. This type of information is critical for establishing reliable diagnostic criteria, such as expression of muscle-specific actin and ultrastructural identification of myofilaments, in these and other salivary gland tumours. Pleomorphic adenomas (18) and myoepitheliomas (5), of which 10 cases were fixed only in formalin and 13 cases where tissues were fixed in both formalin and methanol/acetic acid, were studied. Each tumour and normal accompanying parotid was immunostained with two monoclonal antibodies for smooth muscle actin, HHF35 and MSA. Staining of myoepithelial cells was absent in certain samples of normal gland with both HHF35 (15%) and MSA (69%) when formalin-fixed tissue was used. Using formalin-fixed tissue from 15 pleomorphic adenomas/myoepitheliomas, 2 (14%) had focal positivity with HHF35, while 8 cases (57%) were positive with MSA. However, a certain degree of false positivity was suspected since in samples of normal parotid, both acinar and duct cells were frequently stained, particularly with MSA. With methanol/acetic acid-fixed tissue only 4 of 13 cases (31%) were positive with either MSA or HHF35 and 2 of these only had a minor proportion of the tumour cells expressing muscle-specific actin. Using alcohol-fixed tissue, myoepithelial cells were strongly stained in all examples of normal parotid gland with both anti-actin antibodies. In 5 cases examined by electron microscopy, there was no apparent correlation between immunohistochemical results and the presence or absence of cytoplasmic filament accumulation. The results indicate considerable tumour cell heterogeneity in muscle-specific actin expression and suggest that non-luminal cells in pleomorphic adenomas and the tumour cells in myoepitheliomas may differentiate as classical myoepithelial cells, as partially differentiated (i.e. modified myoepithelial cells) or as the counterpart of basal cells present in the intra- and interlobular ducts of normal salivary gland.

Immunohistochemical studies of S-100 protein alpha and beta subunits in adenoid cystic carcinoma of salivary glands

Immunohistochemical studies were performed to explore the distribution of S-100 protein and its alpha, beta subunits in 76 adenoid cystic carcinomas (ACC) of the salivary glands. Histopathologically. ACC was divided into cribriform, tubular, basaloid and trabecular types which could be mixed in the same tumor. S-100 protein was usually positive in tumor cells forming cribriform structures; foci of strongly positive tumor cells were also distributed in the luminal layer of tubular structures, and in areas transitional between cribriform and tubular patterns. S-100 alpha staining was confined to some tumor cells in cribriform areas, to luminal tumor cells in tubular structures and to few tumor cells in basaloid structures. S-100 beta reaction was usually localized to luminal surfaces in a fine granular pattern in tubular and microtubular structures in a distribution somewhat similar to that in the normal salivary gland. Great heterogeneity in the immunohistochemical distribution of S-100, S-100 alpha and S-100 beta proteins was found in the various histologic types of ACC and the pattern was different from that seen in pleomorphic adenomas. It is possible that the ACC tumor cells positive for S-100 protein may be closely related to true or modified myoepithelial cells.

WHO International Histological Classification of Tumours. Tentative Histological Classification of Salivary Gland Tumours

The principles of the proposed modified WHO Histological Typing of Salivary Gland Tumours are based on the following: 1) The classification of tumours is oriented to the routine work of the practicing surgical pathologists, those who do not see tumours of the salivary glands very often. The inclusion of rare, but clearly defined tumour entities should be helpful to surgical pathologists consulting with clinical specialists. 2) The different types of carcinomas must be distinguished not only by precise histopathological definitions, but also considering differences in prognosis and treatment. For example, the polymorphous low-grade adenocarcinoma and the epithelial-myoepithelial carcinoma are characterized by a relatively good prognosis in contrast to the salivary duct carcinoma. 3) Special points of discussion are: subclassification and grading of carcinomas (e.g. acinic cell carcinoma, mucoepidermoid carcinoma and adenoid cystic carcinoma), the classification of basal cell tumours (basal cell adenoma, basal cell carcinoma, solid type of adenoid cystic carcinoma), malignant tumours in pleomorphic adenomas and the differential diagnosis between primary tumours and metastases.

Multiple expression of keratins, vimentin, and S-100 protein in pleomorphic salivary adenomas

Immunohistochemical staining for S-100 protein and the intermediate filaments keratin and vimentin, was made in 41 salivary adenomas. In pleomorphic adenomas, great heterogeneity in the staining, as well as multiple and co-expressions of these proteins were found in the outer tumor cells of tubulo-ductal structures and modified myoepithelial cells, but not in the luminal tumor cells. All the outer tumor cells stained for S-100 protein, 97% for K8.12 keratin and 85% for vimentin. Of these cells, 29% showed multiple expression of K8.12 keratin, vimentin, and S-100 protein, and 17% showed co-expression of K8.12 and S-100 protein. Modified and neoplastic myoepithelial cells showed similar expressions of these proteins to those of outer tumor cells; myoepithelioma cells displayed the most complicated pattern, being positive for KL1, PKK1, and K8.12 keratins, vimentin and S-100 protein. In luminal tumor cells there was a heterogeneous expression of KL1 and PKK1 in 82%, and of KL1, PKK1, and K8.12 in only 14.7%. Based on the immunohistochemical findings obtained with different monoclonal antibodies in pleomorphic salivary adenomas, outer tumor cells may be derived from ductal basal cells and luminal tumor cells from intercalated duct cells.

Histogenesis of salivary gland neoplasms: a postulate with prognostic implications

In a continually renewing cell population, stem cells can be regarded as a reservoir of cells with a high capacity for self renewal that give rise to all differentiated progeny. They are the primary source for the generation and maintenance of cellular diversity and tissue homeostasis. In general, neoplasms manifest differentiation pathways similar to those found in the development and renewal of the normal tissues from which they arise. This feature serves as a basis for classification schemes of neoplasms and, as in the normal tissues, there is usually an inverse correlation between proliferative capacity and differentiation within the neoplasms. In our postulate of the histogenesis of salivary gland neoplasia, we evoke the stem cell model to account for the considerable phenotypic heterogeneity seen with these neoplasms. We further consider the neoplasms and, in particular, their myoepithelial constituencies to be manifestations of escape from normal regulatory mechanisms that determine differentiation pathways which a stem cell and its progeny can take. Clinical and basic scientific evidence are presented to support the postulate and also to point to the mitigating role that myoepithelial differentiation has in the biological course of salivary gland neoplasms.

Immunohistochemical localization of the alpha and beta subunits of S-100 protein in pleomorphic adenoma of the salivary glands

The immunohistochemical expression of the alpha and beta subunits of S-100 protein in reactive, modified and transformed of myoepithelial cells, salivary pleomorphic was investigated using monoclonal antibodies. With S-100 alpha, normal salivary glands showed strong staining in serous acinar cells and moderate to slight staining in ductal segments, and with S-100 beta staining was slight or negative in acinar cells, but strong in nerve fibres. In pleomorphic salivary adenomas, the immunohistochemical distribution of S-100 alpha and beta proteins indicated great variation in the tumour cells. Some neoplastic cells gave similar staining for both S-100 alpha and beta, others were strongly positive for S-100 alpha and stained only slightly for S-100 beta, or vice versa. Yet other cells were positive for S-100 alpha and negative for S-100 beta, or vice versa. Pleomorphic salivary adenomas were classified both by histopathological criteria and by their staining pattern for S-100 alpha and beta proteins. Great heterogeneity in S-100 alpha and beta protein expression was found in individual tumour cells of both ductal and myoepithelial origin, and no regular pattern was identified. The cellular origin of salivary pleomorphic adenomas is discussed in terms of S-100 alpha and beta protein immunohistochemistry. Pleomorphic adenoma cells may be transformed from reserve cells into tumour cells displaying biologic properties of myoepithelial cells, ductal cells, or a mixture of both.