Ultrastructural similarities of adenoid cystic carcinoma and pleomorphic adenoma

Activation of PLAG1 and HMGA2 by gene fusions involving the transcriptional regulator gene NFIB

The pleomorphic adenoma (PA), which is the most common salivary gland neoplasm, is a benign tumor characterized by recurrent chromosome rearrangements involving 8q12 and 12q14-15. We have previously shown that the PLAG1 and HMGA2 oncogenes are the targets of these rearrangements. Here, we have identified previously unrecognized subsets of PAs with ins(9;8)/t(8;9) (n = 5) and ins(9;12)/t(9;12) (n = 8) and breakpoints located in the vicinity of the PLAG1 and HMGA2 loci. RNA-sequencing and reverse transcriptase (RT)-PCR analyses of a case with an ins(9;8) revealed a novel NFIB-PLAG1 fusion in which NFIB exon 4 is linked to PLAG1 exon 3. In contrast to the developmentally regulated PLAG1 gene, NFIB was highly expressed in normal salivary gland, indicating that PLAG1 in this case, as in other variant fusions, is activated by promoter swapping. RT-PCR analysis of three PAs with t(9;12) revealed two tumors with chimeric transcripts consisting of HMGA2 exon 4 linked to NFIB exons 9 or 3 and one case with a fusion linking HMGA2 exon 3 to NFIB exon 9. The NFIB fusion events resulted in potent activation of PLAG1 and HMGA2. Analysis of the chromatin landscape surrounding NFIB revealed several super-enhancers in the 5'- and 3'-parts of the NFIB locus and its flanking sequences. These findings indicate that PLAG1 and HMGA2, similar to MYB in adenoid cystic carcinoma, may be activated by enhancer-hijacking events, in which super-enhancers in NFIB are translocated upstream of PLAG1 or downstream of HMGA2. Our results further emphasize the role of NFIB as a fusion partner to multiple oncogenes in histopathologically different types of salivary gland tumors.

Pleomorphic Adenoma and Adenoid-Cystic Carcinoma of the Salivary Glands: Comparative Immunohistochemical Patterns

A series of 20 cases of pleomorphic adenoma and 19 cases of adenoid-cystic carcinoma of the salivary glands, and one case in the mammary location, were investigated regarding immunohistochemical reactivity for Tissue Polypeptid Antigen (TPA), Pre-Keratins, Vimentin, S-100 Protein, and their arrangement pattern of fibronectin.

As a whole, the results support the hypothesis of morpho-structural and mainly, onto-histogenetic similarities between these tumours, but they also underline the need for great care in outlining their morpho-functional features, in relation to their different prognoses.

Evaluation of p27 Expression in Salivary Gland Neoplasms; A Step Forward in Unveiling the Role of p27

INTRODUCTION

Salivary gland neoplasms are not uncommon lesions that are seen in the head and neck region. The role of cell cycle regulators as well as that of oncogenes remains unexplored in the pathogenesis of these neoplasms.

AIM

Present study was conducted to evaluate the expression of p27 in the three common salivary gland neoplasms.

MATERIALS AND METHODS

A total of 34 cases (19 pleomorphic adenoma, 8 mucoepidermoid carcinoma and 7 adenoid cystic carcinoma) were included. The sections were subjected to p27 staining and rated for the expression.

RESULTS

Of the total 52.6% of pleomorphic adenoma cases, 25% of mucoepidermoid carcinoma cases and only 14.2% of adenoid cystic carcinoma cases showed strong expression suggesting variable p27 expression in both malignant neoplasms. Normal salivary gland tissue was stained as a positive control for the evaluation.

CONCLUSION

The results of the study suggest an important role for p27 in pathogenesis of mucoepidermoid carcinoma as well as adenoid cystic carcinoma while its role in pathogenesis of pleomorphic adenoma remains questionable keeping in view the strong expression of p27 in the same.

PLAG1 and CYLD do not play a role in the tumorigenesis of adenoid cystic carcinoma

The pleiomorphic adenoma gene 1 (PLAG1) gene is activated in a subset of pleomorphic adenomas of the salivary gland by gene fusion. Germ‑line mutation in cylindromatosis (CYLD), a tumor suppressor gene, causes familial cylindromatosis and Brook‑Spiegler syndrome. In the present study, aberrations in PLAG1 and CYLD were investigated in adenoid cystic carcinoma (ACC) of the salivary gland. Reverse‑transcription PCR and PCR direct sequencing were performed to detect gene fusion of PLAG1 and mutation of CYLD in 34 ACC tissues. No PLAG1 fusion was detected in ACC. However, silent mutation of CYLD was detected in 2 cases of ACC, but no missense mutation was detected in ACC. These results suggest that PLAG1 and CYLD do not play a role in ACC tumorigenesis.

Extracellular material in adenoid cystic carcinoma of the salivary glands: A comparative cytological study with other salivary myoepithelial tumors

The objective of this study was to clarify extracellular materials (ECMs) in adenoid cystic carcinoma (AdCC) and compare these to those found in other salivary gland tumors with myoepithelial differentiation. The ECM was examined with Papanicolaou, May-Grünwald-Giemsa (MGG), and alcian blue stain at pH 2.5. The ECM in AdCC was classified into three types according to their staining patterns: clear, hyalinized, and membrane type. The incidence of clear-type globule material with magenta on MGG was low in other salivary gland tumors with myoepithelial differentiation. The ECM was identified in other salivary gland tumors with myoepithelial differentiation. However, AdCC has the greatest variety of ECM. These findings are useful to understand the character of AdCC and differential diagnosis of the other salivary gland tumors with myoepithelial differentiation.

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.

Adenoid cystic carcinoma of the breast: molecular markers, treatment, and clinical outcome

BACKGROUND

The objective of this study was to comprehensively characterize the clinical and biologic features of adenoid cystic carcinoma (ACC) and to assess the implications for management in a large cohort of patients.

METHODS

From a database of 50,000 patients, 28 were identified with ACC for which clinical follow-up and biologic information was available. The biologic features examined included estrogen receptor and progesterone receptor status, DNA ploidy, and S-phase fraction. Median follow-up was 83 months with a range of 29 to 144 months. Overall survival and disease free survival curves were drawn using Kaplan and Meier estimates and were compared by the log-rank test.

RESULTS

All but one patient were postmenopausal with a median age at diagnosis of 66 years (range, 40-96 years). One patient had macroscopic metastatic disease at diagnosis. Median tumor size was 1.9 cm (range, 0.5-7.0 cm). Axillary lymph node dissection was performed in 23 patients. Only 1 patient (4%) had histologic positive lymph nodes (2 of 10), and no recurrence was detected for this patient. Forty-six percent were ER positive (median, 16 fmol/mg protein; range, 5-1017 fmol/mg), and 35% were PgR positive (median, 61 fmol/mg protein; range, 6-854 fmol/mg). S-phase fraction and DNA ploidy were assessable in 24 cases. Ninety percent of tumors had low S-phase (median, 3.3%; range, 0.1-34.2%), and 92% were diploid. Simple or modified radical mastectomy was performed in 22 patients, and 6 patients were treated by lumpectomy. Five of these six patients also received radiation therapy after lumpectomy. Despite the different surgical approaches, there were no local recurrences. The 5-year disease free survival rate was 100%, and the 5-year overall survival rate was 85% (95% confidence interval, 71.7-98.6%).

CONCLUSIONS

Adenoid cystic carcinomas of the breast have very favorable biologic characteristics and, consistent with this, an excellent prognosis. Good local control can be achieved by lumpectomy with radiation or by simple mastectomy. Axillary lymph node dissection is not helpful in clinical management.

Fine-needle aspiration biopsy of adenoid cystic carcinoma of the breast: a case report

We describe the cytologic findings of a fine-needle aspiration (FNA) breast lesion with a typical histology for adenoid cystic carcinoma. The aspirate yielded highly cellular smears with a monomorphic population of small, slightly atypical cells, arranged in multilayered groups with abundant fine intercellular metachromatic substance between cell groups. There were also fragments of fibrillar stroma in close relation to epithelial cells. The diagnosis based on the FNA material was suspicious of malignancy. The cytomorphology in this case presented a difficult differential diagnosis with pleomorphic adenoma. Features indicative of adenoid cystic carcinoma were nuclear cell hyperchromasia, the presence of small nucleoli, and scant, poorly defined, or absent cytoplasms. Differential diagnosis of breast adenoid cystic carcinoma with other entities will also be discussed.

Polymorphous low-grade adenocarcinoma arising in the nasal cavities with an associated undifferentiated carcinoma

A case of polymorphous low-grade adenocarcinoma arising in the right nasal cavity of a male patient with previous history of kidney transplantation is reported. The tumor contained extensive areas of undifferentiated carcinoma, probably arising from the low-grade component. This combination of findings has not been previously reported in this variety of salivary gland tumor.

Ultrastructural distinction of basaloid-squamous carcinoma and adenoid cystic carcinoma

Basaloid-squamous carcinoma is a unique and infrequent variant of squamous cell carcinoma with a predilection for occurring in the upper aerodigestive tract. The cardinal diagnostic criteria are the presence of basaloid cells arranged in lobules or cords and a squamous component. Another feature that distinguishes basaloid-squamous carcinoma from conventional squamous cell carcinoma is the development of multiple foci of amorphous, eosinophilic, or mucinous materials among the basaloid tumor cells. It is this feature in basaloid-squamous carcinoma that causes confusion with adenoid cystic carcinoma, especially the solid variant of adenoid cystic carcinoma. To clarify the distinctive features of these two types of tumors, the ultrastructural findings in three basaloid-squamous carcinomas from the head and neck region were compared with three adenoid cystic carcinomas, one from the head and neck region and one each from trachea and bronchus. Widened intercellular spaces, tonofilaments, and replicated basal lamina were present in both types of tumor. However, the ultrastructural features of glandular differentiation were present only in adenoid cystic carcinoma, whereas the ultrastructural features of squamous cell differentiation were present only in basaloid-squamous carcinoma. The distinction between basaloid-squamous carcinoma and adenoid cystic carcinoma is important since basaloid-squamous carcinoma is a clinically aggressive, high-grade form of squamous cell carcinoma, generally with a worse prognosis than adenoid cystic carcinoma.

Myofilament localization and immunoelectron microscopic detection of muscle-specific actin in neoplastic myoepithelial cells in pleomorphic adenomas and myoepitheliomas

Elucidating the cellular characteristics of the nonluminal or myoepithelial cells of pleomorphic adenomas is one approach to establishing the diagnostic criteria for myoepitheliomas. Ultrastructural features of nonluminal tumor cells in 22 pleomorphic adenomas and of tumor cells in 9 myoepitheliomas were assessed from micrographs of routinely fixed and epoxy resin-embedded samples. Recognizable myofilaments were only moderately prominent in 1 myoepithelioma. In the rest of the cases, irrespective of whether nonluminal cells of pleomorphic adenomas or tumor cells of myoepitheliomas were spindle, angular, round, or plasmacytoid in form, myofilaments were noted only in one third of the cases and were present even in these in a small proportion of the tumor cells. Intermediate filament accumulations and basal lamina were more frequent findings associated with nonluminal tumor cells. Six pleomorphic adenomas and 2 myoepitheliomas had been fixed in half-strength glutaraldehyde and embedded in LR White resin for immunoelectron microscopic detection of muscle-specific actin. In 3 (2 pleomorphic adenomas and myoepitheliomas) of these 8 cases, readily visualized bands of filaments in many tumor cells were strongly labeled by the colloidal gold probe detecting muscle-specific actin even when myofilaments were minimal and infrequent in 2 cases and undetectable in the third by routine transmission electron microscopy. Lack of myofilament detection by immunocytochemistry or routine electron microscopy does not exclude a diagnosis of pleomorphic adenoma or myoepithelioma when growth patterns and cytology indicate such diagnoses. Immunoelectron microscopy, in fact, shows that muscle-specific actin can be detected even when myofilaments or muscle actin are apparently absent or minimal by routine electron microscopy or immunohistochemistry, respectively. Because examples of pleomorphic adenoma and myoepithelioma each with similar histologic and cytologic features of the myoepitheliomatous cells can have variable degrees or complete absence of expression of myofilaments or muscle-specific actin, the time-honored term myoepithelial for the nonluminal cells of pleomorphic adenomas and the term myoepithelioma are legitimate even in the absence of those markers that are specific for normal myoepithelial cells.

Maxillary adenoid cystic carcinoma with annulate lamellae

Of 29 reviewed ultrastructural studies of adenoid cystic carcinoma, only 1 mentions the presence of annulate lamellae. The present report describes a 65-year-old woman who presented with an adenoid cystic carcinoma in her left maxillary sinus. At the light microscopic level, most of the connective tissue was loose and myxomatous and contained fine strands, cords, and islands of epithelium that in places had a cribriform pattern. The ultrastructural appearance was similar to that described by others. Two epithelial cell types predominated. The cytoplasm of one type contained mainly ribosomes, and that of the other type also had peripheral microfilaments. Also present were pseudocysts, lumina with microvilli, and replicated basal lamina. In addition, a number of both types of cells contained parallel arrays of cisternae that had regular small pores. These were annulate lamellae.

Pathology of the salivary glands: the contribution of electron microscopy

Electron microscopy has a limited role in the diagnosis of primary salivary gland tumors, although it can be helpful in metastatic lesions of possible salivary gland origin. The diversity of subtypes in salivary gland tumors, as well as the range of histomorphology within any one subtype, is unparalleled in any other human tumor. This and their relative infrequency causes diagnostic problems for pathologists. Ultrastructural techniques have been of major importance in determining the inter-relationship of these tumors for classification purposes, revealing the subtle variations in common cellular differentiation pathways, determining the organization of tumor cells, and displaying the importance of extracellular matrix materials in establishing diagnostic criteria for each of the many subtypes. Electron microscopy has also been valuable in non-neoplastic salivary gland disease and has an increasing role in experimental studies involving tissue from human and animal salivary parenchyma.

Comparative cytofluorometric DNA analysis of pleomorphic adenoma and adenoid cystic carcinoma of the salivary glands

The nuclear DNA content in the tumor cells of 17 pleomorphic adenomas (PA) and 26 adenoid cystic carcinomas (ACC) was assayed by cytofluorometry to clarify the etiology of the differences in their biological nature. Aneuploidy was found in only two solid-pattern ACC samples; all the other samples had diploid stemlines. With respect to the polyploid cell rate and the S + G2M fraction, the differences between the four histological patterns of PA were not significant. In the ACC, the S + G2M fraction was significantly higher in solid pattern than in cribriform or trabecular pattern tumors, which may indicate that proliferative activity is higher in the solid pattern than in the other two. The polyploid cell rate in ACC was significantly higher in the solid pattern than in the cribriform pattern carcinomas. There was no significant difference in the mean polyploid cell rate between PAs and ACCs. The mean S + G2M fraction was significantly higher in all histological patterns of ACCs than in PAs. These results suggest that proliferative activity is greater in any one of the histological patterns of ACC than in PA. These findings may largely explain the biological differences between the two tumors.

Pleomorphic adenoma of the human female breast

We are presenting an interesting rare benign breast tumor which meets the characteristics of a salivary gland pleomorphic adenoma. The tumor was misdiagnosed during frozen section procedure, because several clusters, mainly composed of myoepithelial cells and surrounded by a chondroid matrix, were mistaken for cancerous blasts. Additionally the clinical and mammographic findings were very suspicious. Although this particular tumor is very infrequent, the pathologist should be aware of the difficulties in the differential diagnosis during frozen section and thus defer his final answer to the paraffin sections.

Trabecular and solid-cribriform types of basal cell adenoma. A morphologic study of two cases of an unusual variant of monomorphic adenoma

Monomorphic adenomas are a morphologically complex group of salivary gland tumors. Two unusual examples, one a trabecular and the other a solid form of basal cell adenoma, reveal the development of a cribriform growth pattern focally in the former example and diffusely in the latter. They illustrate the potential for cellular differentiation within this subgroup, organization of synthetic products by the tumor cells, and the histologic criteria useful for the distinction of basal cell adenoma from adenoid cystic carcinoma.

Nuclear ultrastructure of human parotid gland tumors with special focus on nuclear bodies

The purpose of our study was to determine the morphology and the proportion of NB in 20 human parotid gland tumors. Types I and III NB were observed in benign as well as malignant tumors. Some atypical forms ("onion-like" NB and NB with lipidic inclusions) were found in benign tumors. The proportion of nuclear profiles containing one and more NB varied from 0 to 60% in the benign tumors, and from 4 to 50% in the malignant tumors. Nuclei containing 3 and more NB were observed as well in the benign as in the malignant tumors. The NB ratio cannot be taken for a malignancy criteria.

Electron microscopic study of adenoid cystic carcinoma

This ultrastructural study is based on nine cases of adenoid cystic carcinoma arising from the salivary glands. Electron microscopically, the tumors consisted of five cell types: relatively differentiated intercalated duct cells, secretory cells, undifferentiated cells, cells of a squamous nature, and myoepithelial cells. Special attention was paid to the characteristic extracellular substances noted by light microscopic examination of these tumors. The hyaline material of the pseudocysts contained not only mucopolysaccharide granules but also fingerprint-like structures formed by replicated basement membrane. Some of these structures had a dense core, probably composed of mucopolysaccharide granules. Cell islands surrounded by elasticlike material also were found. The true lumina were usually filled with membranovesicular structures originating from fragments of the lining cells, mainly those with squamous differentiation. These membranovesicular structures included electron-dense rods, filamentous whorls, and structures displaying periodicity.

Comparative histogenesis and morphogenesis of mucoepidermoid carcinoma and pleomorphic adenoma. An ultrastructural study

Current classifications of salivary gland tumors separate mucoepidermoid carcinoma from other neoplasms on the basis of a number of histological features, in particular the lack of participation of neoplastic myoepithelial cells. However, ultrastructural examination of low- and intermediate-grade mucoepidermoid carcinomas and pleomorphic adenomas reveals many common organizational and cellular features. Of prime importance is the relationship of intermediate cells to the luminal cells in mucoepidermoid carcinomas, which is remarkably similar to that seen between modified myoepithelial cells and luminal cells in pleomorphic adenomas. The results suggest that intermediate cells of mucoepidermoid carcinoma are the counterpart of the modified myoepithelial cells of pleomorphic adenoma. The generally accepted hypothesis that the former tumor develops from an excretory duct reserve cell, while the latter originates from an intercalated duct stem cell does not seem to be valid; pleomorphic adenoma and mucoepidermoid carcinoma appear to be closely related morphologically.

Characterisation of adenoid cystic carcinoma of the breast by immunohistology

An adenoid cystic carcinoma of the breast in a 78 year old woman was analysed immunohistologically for the production of type IV collagen, the expression of vimentin, epithelial membrane antigen (EMA) and steroid receptors, and the proliferative activity of the tumour cells. The data were compared with those obtained in eight adenoid cystic carcinomas of salivary glands and in ductal carcinomas of the breast with a cribriform growth pattern. The patients' ages were as follows: 45-80 years (mean 63.2) for the salivary gland carcinomas; 37-69 years (mean 50.6) for the ductal breast carcinomas. In contrast to the cribriform spaces of ductal carcinomas, the pseudocysts in adenoid cystic carcinomas were lined by type IV collagen. The opposite pattern was observed for EMA. Like the myoepithelium of normal breast, the myoepithelium-like cells of adenoid cystic carcinoma stained positive for vimentin while the ductular epithelium-like ones did not. All adenoid cystic carcinomas, including that of the breast, were negative for the oestrogen and progesterone receptors, unlike the ductal carcinomas. Proliferative activity of the adenoid cystic carcinoma of the breast was relatively low. These data broaden the range of antibodies suitable for differential diagnosis of both tumour types. They may explain the differences in prognosis, and they explain why hormonal treatment or radiotherapy of adenoid cystic carcinoma of the breast are often ineffectual.

Myoepithelioma--new concepts of histology and classification: a light and electron microscopic study

Based on histological, immunohistochemical, and ultrastructural studies, it is now apparent that the modified myoepithelial cell component of pleomorphic adenomas has a considerable range of cytological features. We reasoned that myoepitheliomas could be tumors with a similar spectrum of neoplastic myoepithelium but lacking the ductal element displayed in pleomorphic adenomas. A review of available salivary gland tumors identified 40 examples based on this definition. Architecturally, these myoepitheliomas displayed either nonmyxoid (solid), myxoid (pleomorphic adenoma-like), reticular (canalicularlike), or mixed growth patterns, while cytologically the lesions were composed of spindle-type (32.5%), hyaline-type (7.5%), epithelial-type (45.0%), clear-type (2.5%), or mixed-type (12.5%) tumor cells. Electron microscopy was carried out on eight examples and detailed immunohistochemistry on two methanol-fixed cases. As a result of the current review of myoepitheliomas and the description of similar lesions in the literature, it is our contention that salivary gland myoepitheliomas are not as rare as has been purported.

Salivary gland myoepithelioma variants. Histological, ultrastructural, and immunocytological features

The histological and ultrastructural features of five major salivary gland tumours, which have little or no evidence of duct- or gland-type differentiation in routine sections, are described. Four of the cases have the tumour cells organized as narrow, anastomosing cords of cells separated by a myxoid and vascularized stroma; we have designated such lesions as reticular-type myoepitheliomas. The fifth case has a solid growth pattern and is largely composed of hyaline cells, that is, a plasmacytoid myoepithelioma. Ultrastructurally, one reticular myoepithelioma reveals myoepithelial cell differentiation with microfilament aggregates, while the other three examples are composed of modified myoepithelial cells displaying widened intercellular spaces, prominent synthesis of extracellular glycosaminoglycans, distinct basal lamina development, and obvious accumulations of cytoplasmic intermediate filaments. In electron micrographs, the modified myoepithelial cells of the plasmacytoid variant closely resemble the tumour cells in the reticular form. Three cases had expression of both glial fibrillary acid protein (GFAP) and vimentin, but only one of the myoepitheliomas contained muscle-specific actin. At least focally, each of the cases exhibited a considerable spectrum of cytokeratin filaments. Using double-labeled immunofluorescent microscopy of one reticular variant and the plasmacytoid myoepithelioma, there was individual tumour cell co-expression of GFAP and vimentin focally in the plasmacytoid myoepithelioma, but co-expression of cytokeratins 13, 16 and GFAP were not noted in either case. As expected, co-expression of high- and low-molecular weight cytokeratin filaments was widespread in both myoepitheliomas. Most described myoepitheliomas have a solid growth pattern and are composed of spindle and plasmacytoid cells, but based on cytological features and growth patterns in this series, it is apparent that polygonal-shaped cells with novel architecture can occur in myoepitheliomas. The results also indicate the close relationship between pleomorphic adenoma and such variants of myoepithelioma.

Ultrastructural contributions to the study of morphological differentiation in malignant mixed (pleomorphic) tumors of salivary gland

Ultrastructural studies of pleomorphic adenoma have shown a coordinated differentiation of luminal epithelial and modified myoepithelial cells with the latter cells related to processes resulting in the myxochondroid stroma. Five examples of various histologic types of malignant mixed tumor of parotid origin were examined by electron microscopy to see if underlying patterns of tumor cell differentiation and organization matched those of pleomorphic adenoma. Whether they were intracapsular tumors (with or without identifiable pleomorphic adenoma), carcinomas ex pleomorphic adenoma, or a true malignant mixed tumor, all lesions had cell types and organizations either identical to those in pleomorphic adenoma or, as in less-differentiated examples, displayed features suggesting origin from luminal cells, myoepithelial cells, or both. Even the chondroid cells in the true malignant mixed tumor expressed ultrastructural features indicating their epithelial derivation. On the basis of these findings, some alterations to the classification and terminology of the subtypes of malignant mixed tumor are suggested.

Adenoid cystic carcinoma of the salivary glands: an immunohistochemical analysis

Adenoid cystic carcinoma is a specific variant of adenocarcinoma with a characteristic cribriform appearance. The tumor may arise from salivary glands and various other sites, but the origin and cellular composition of this unique neoplasm have been controversial. A potential use of immunohistochemistry is to provide additional information on the origin of various cellular components of tumors by comparing them with corresponding normal tissues. Immunohistochemical distributions of carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA), keratin, low molecular weight keratin (54 kd), S100 protein, muscle-specific actin, laminin, and type IV collagen were evaluated in 20 adenoid cystic carcinomas arising in major and minor salivary glands. Anti-CEA, anti-EMA, anti-keratin, and anti-S100 antibodies strongly stained cells lining true lumina. Muscle-specific actin, a marker for myoepithelial cells, was found in lining cells of pseudocysts, in tumor cells proper, and in nonluminal cells with a tubular growth pattern. A monoclonal antibody against 54 kd keratin stained almost all cells in the neoplasms. In pseudocysts, replicated basal lamina reacted with antisera to laminin and to type IV collagen. The present study demonstrates that there are at least two populations of tumor cells in adenoid cystic carcinoma: luminal cells that express CEA and EMA, thus indicating their ductal character, and nonluminal cells that express muscle-specific actin characteristic of myoepithelium.

Normal and neoplastic myoepithelial cells in salivary glands: an immunohistochemical study

To determine the difference between normal and neoplastic myoepithelial cells, we performed immunoperoxidase staining for contractile proteins (actin and myosin) and intermediate filament proteins (vimentin and 55- to 57-kilodalton keratin) on paraffin sections from salivary gland tumors. Normal myoepithelial cells were positive for actin and myosin but negative for vimentin and keratin. Outer tubular cells of organoid double-layered tubular structures seen in pleomorphic and monomorphic adenoma and adenoid cystic carcinoma, and "cyst"-lining cells and outermost cells of adenoid cystic carcinoma were occasionally positive for actin and myosin. These outer tubular cells, "cyst"-lining cells, and outermost cells were considered to be neoplastic myoepithelial cells. However, their stainability was much lower than that of normal myoepithelial cells. On the other hand, these neoplastic myoepithelial cell were always positive for vimentin. "Mesenchymal" cells and hyaline cells of pleomorphic adenoma and indifferent cells of adenoid cystic carcinoma were negative for both actin and myosin but positive for vimentin and occasionally also positive for keratin. The significance of vimentin staining in neoplastic myoepithelial cells and the coexpression of vimentin and keratin in some tumor cells is discussed.

The cellular composition of adenoid cystic carcinoma. An immunohistochemical study

To investigate the cellular differentiation of adenoid cystic carcinomas (ACC), a comparative immunohistochemical study of 12 normal salivary glands and eight specimens of ACC was performed. Antibodies were used against S100 protein (S), keratins (K) of various molecular weights, vimentin (V), muscle-specific actin (A), epithelial-membrane antigen, human milk fat globules, and collagen type IV. A panel of four of these antibodies (SKVA) was identified as the most helpful in characterizing cells in normal salivary glands and ACC. The immunophenotypes depended on the histologic patterns of ACC. Cells in morphologically recognizable duct structures in the cribriform and trabecular areas expressed a phenotype similar to that of the intercalated duct. Cell layers around pseudocysts and occasional cellular islands had an immunophenotype suggesting myoepithelial-cell differentiation. The most clear cut epithelial/myoepithelial bilaminar differentiation was present in areas with a trabecular pattern, in which the layers facing the stroma and the central ductal elements had SKVA phenotypes of myoepithelial and ductal differentiation, respectively. In areas with a reticular pattern, most of the cells showed ductal differentiation. Many of the cells in the cribriform and basaloid regions were immunophenotypically undifferentiated. These results indicate that ACC consists of undifferentiated cells and of cells that are differentiating toward ducts, predominantly intercalated ducts, and toward myoepithelium. These findings support previous observations by electron microscope.

Ultrastructural morphology and cellular differentiation in acinic cell carcinoma

Acinic cell carcinomas, in some instances, contain a component of intercalated duct cells. However, the manner in which this element is integrated within the more obvious acinar cells, as well as the role neoplastic intercalated duct cells play in determining morphologic patterns in acinic cell tumors, has not been fully investigated. Ultrastructural study and immunostaining with antibodies to cytokeratins and to S-100 protein carried out in nine cases of parotid acinic cell carcinoma suggest two basic differentiation patterns. In three cases, the lesions were essentially composed of acinar cells (with variation in the number and form of secretory granules), and one of these tumors was unique in having ultrastructural evidence of differentiated myoepithelial cells. In the second group of six cases, there was light microscopic, ultrastructural, and immunohistochemical evidence of a significant component of intercalated duct cells. By means of both immunostaining (intercalated ducts were positive for keratin and S-100 protein; acinar cells were negative for both antigens) and electron microscopy, flattened-to-cuboidal intercalated duct cells were noted to enclose and, presumably, to be involved in the formation of microcystic spaces. Acinic cell carcinomas with a more solid growth pattern contained groups of intercalated duct cells positive for keratin and S-100 protein. Ultrastructurally, these cells were organized into well-formed ducts related to nests of acinar cells. Acinic cell carcinoma is another class of salivary gland tumor in which there can be an integrated proliferation of intercalated duct and acinar cells and, infrequently, of myoepithelial cells, all organized in a simulation of the intercalated duct-acinar unit of the normal salivary gland.