Pathogenesis Of Adenoid Cystic Carcinoma Research Articles

Molecular Analysis of Salivary and Lacrimal Adenoid Cystic Carcinoma.

Adenoid cystic carcinoma (ACC) of head and neck origin is associated with slow but relentless progression and systemic metastasis, resulting in poor long-term survival rates. ACC does not respond to conventional chemotherapy. Determination of molecular drivers may provide a rational basis for personalized therapy. Herein, we investigate the clinical and detailed molecular genomic features of a cohort of patients treated in Ireland and correlate the site of origin, molecular features, and outcomes. Clinical and genomic landscapes of all patients diagnosed with ACC over a twenty-year period (2002-2022) in a single unit in Ireland were examined and analyzed using fluorescence in situ hybridization, DNA sequencing, and bioinformatic analysis. Fourteen patients were included for analysis. Eleven patients had primary salivary gland ACC and three primary lacrimal gland ACC; 76.9% of the analyzed tumors displayed evidence of NFIB-MYB rearrangement at the 6q23.3 locus; 35% had mutations in NOTCH pathway genes; 7% of patients had a NOTCH1 mutation, 14.3% NOTCH2 mutation, and 14.3% NOTCH3 mutation. The presence of epigenetic modifications in ACC patients significantly correlated with worse overall survival. Our study identifies genetic mutations and signaling pathways that drive ACC pathogenesis, representing potential molecular and therapeutic targets.

MYB immunohistochemistry as a predictor of MYB::NFIB fusion in the diagnosis of adenoid cystic carcinoma of the head and neck

Diagnosing adenoid cystic carcinoma (AdCC) is challenging due to histopathological variability and similarities with other tumors. In AdCC pathogenesis, the cellular myeloblastosis gene (c-MYB) often exhibits a MYB::NFIB fusion from a reciprocal translocation. This study aimed to assess the predictive accuracy of MYB immunohistochemistry for detecting this translocation compared to fluorescence in situ hybridization (FISH). This study included 110 AdCC patients (1999-2017) from two Dutch head and neck centers using tissue microarrays and full slides. Median MYB expression levels by immunohistochemistry were compared based on translocation status by FISH, and differences within clinicopathological parameters were examined. An immunohistochemical cut-off was established to estimate the translocation. MYB immunohistochemistry was available in 90/110 patients, with a median expression of 27%. FISH was interpretable in 79/108 tumors, identifying MYB::NFIB fusion in 44 (56%). Among 62 patients with both MYB expression and translocation data, the fusion was present in 38 (61%). These tumors had higher MYB expression (30%) than nontranslocated tumors (6%); P = .02. A 60% MYB expression cut-off yielded 100% specificity for detecting the translocation but had no prognostic value. Although MYB protein expression alone lacks diagnostic precision, protein expression >60% predicted the MYB::NFIB fusion in all tumors.

Wnt/β-catenin-C-kit axis may play a role in adenoid cystic carcinoma prognostication

Adenoid cystic carcinoma (ACC) is one of the most common malignant salivary gland tumors. ACC is composed of myoepithelial and epithelial neoplastic cells which grow slowly and have a tendency for neural invasion. The long term prognosis is still relatively poor. Although several gene abnormalities, such as fusions involving MYB or MYBL1 oncogenes and the transcription factor gene NFIB, and overexpression of KIT have been reported in ACC, their precise functions in the pathogenesis of ACC remain unclear. We recently demonstrated that the elevated expression of Semaphorin 3A (SEMA3A), specifically expressed in myoepithelial neoplastic cells, might function as a novel oncogene-related molecule to enhance cell proliferation through activated AKT signaling in 9/10 (90%) ACC cases. In the current study, the patient with ACC whose tumor was negative for SEMA3A in the previous study, revisited our hospital with late metastasis of ACC to the cervical lymph node eight years after surgical resection of the primary tumor. We characterized this recurrent ACC, and compared it with the primary ACC using immunohistochemical methods. In the recurrent ACC, the duct lining epithelial cells, not myoepithelial neoplastic cells, showed an elevated Ki-67 index and increased cell membrane expression of C-kit, along with the expression of phosphorylated ERK. Late metastasis ACC specimens were not positive for β-catenin and lymphocyte enhancer binding factor 1 (LEF1), which were detected in the nuclei of perineural infiltrating cells in primary ACC cells. In addition, experiments with the GSK-3 inhibitor revealed that β-catenin pathway suppressed not only KIT expression but also proliferation of ACC cells. Moreover, stem cell factor (SCF; also known as KIT ligand, KITL) induced ERK activation in ACC cells. These results suggest that inactivation of Wnt/β-catenin signaling may promote C-kit-ERK signaling and cell proliferation of in metastatic ACC.

Comprehensive molecular characterization of adenoid cystic carcinoma reveals tumor suppressors as novel drivers and prognostic biomarkers.

Adenoid cystic carcinoma (ACC) is a MYB-driven head and neck malignancy with high rates of local recurrence and distant metastasis and poor long-term survival. New effective targeted therapies and clinically useful biomarkers for patient stratification are needed to improve ACC patient survival. Here, we present an integrated copy number and transcriptomic analysis of ACC to identify novel driver genes and prognostic biomarkers. A total of 598 ACCs were studied. Clinical follow-up was available from 366 patients, the largest cohort analyzed to date. Copy number losses of 1p36 (70/492; 14%) and of the tumor suppressor gene PARK2 (6q26) (85/343; 25%) were prognostic biomarkers; patients with concurrent losses (n = 20) had significantly shorter overall survival (OS) than those with one or no deletions (p < 0.0001). Deletion of 1p36 independently predicted short OS in multivariate analysis (p = 0.02). Two pro-apoptotic genes, TP73 and KIF1B, were identified as putative 1p36 tumor suppressor genes whose reduced expression was associated with poor survival and increased resistance to apoptosis. PARK2 expression was markedly reduced in tumors with 6q deletions, and PARK2 knockdown increased spherogenesis and decreased apoptosis, indicating that PARK2 is a tumor suppressor in ACC. Moreover, analysis of the global gene expression pattern in 30 ACCs revealed a transcriptomic signature associated with short OS, multiple copy number alterations including 1p36 deletions, and reduced expression of TP73. Taken together, the results indicate that TP73 and PARK2 are novel putative tumor suppressor genes and potential prognostic biomarkers in ACC. Our studies provide new important insights into the pathogenesis of ACC. The results have important implications for biomarker-driven stratification of patients in clinical trials. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Immunoexpression of Autophagy-Related Proteins in Salivary Gland Tumors: An Exploratory Study.

Autophagy is a cellular survival mechanism involved in several human diseases, but its participation in the development of salivary gland tumors is not fully understood. This study investigated the immunoexpression of autophagy-related proteins (autophagy-related 7 [Atg7], microtubule-associated protein 1 light chain 3A [LC3A], microtubule-associated protein 1 light chain 3B [LC3B], protein p62 [p62], and phosphorylated mammalian target of rapamycin [p-mTOR]) in pleomorphic adenoma (PA), polymorphous adenocarcinoma (PAC), mucoepidermoid carcinoma (MEC), and adenoid cystic carcinoma (ACC) of salivary glands. Twenty PAs, 20 PACs, 20 MECs, and 14 ACCs were selected. The percentages of cytoplasmic and nuclear positivity for autophagy-related proteins in neoplastic cells were assessed and correlated with histopathological parameters. Cytoplasmic immunoexpression of Atg7 was observed in all groups, with high median percentages of positivity. Regarding LC3A and LC3B, cytoplasmic immunoexpression was found in most PACs (95%) and in all cases of PA, MEC and ACC, with the highest percentages of positivity in PACs and PAs (p < 0.005). ACCs exhibited lower cytoplasmic immunoexpression of p-mTOR (p < 0.005) and lower nuclear expression of p62 (p < 0.05) when compared to PAs, PACs and MECs. Low nuclear immunoexpression of Atg7, LC3A and p-mTOR and absence of nuclear staining for LC3B were observed in all groups. Regarding histopathological parameters of PAs, MECs and ACCs, there were no significant differences in the expression of autophagy-related proteins. In all groups, positive correlations were observed between the immunoexpression of some autophagy-related proteins (p < 0.05). The results suggest the participation of autophagy in the pathogenesis of PA, PAC, MEC, and ACC of salivary glands. Upregulation of autophagy and reduced nuclear translocation of p62 may contribute to the aggressive biological behavior of salivary gland ACC.

The Semaphorin 3A-AKT axis-mediated cell proliferation in salivary gland morphogenesis and adenoid cystic carcinoma pathogenesis

We recently demonstrated that Semaphorin 3 A (Sema3A), the expression of which is negatively regulated by Wnt/β-catenin signaling, promotes odontogenic epithelial cell proliferation, suggesting the involvement of Sema3A in tooth germ development. Salivary glands have a similar developmental process to tooth germ development, in which reciprocal interactions between the oral epithelium and adjacent mesenchyme proceeds via stimulation with several growth factors; however, the role of Sema3A in the development of salivary glands is unknown. There may thus be a common mechanism between epithelial morphogenesis and pathogenesis; however, the role of Sema3A in salivary gland tumors is also unclear. The current study investigated the involvement of Sema3A in submandibular gland (SMG) development and its expression in adenoid cystic carcinoma (ACC) specimens. Quantitative RT-PCR and immunohistochemical analyses revealed that Sema3A was expressed both in epithelium and in mesenchyme in the initial developmental stages of SMG and their expressions were decreased during the developmental processes. Loss-of-function experiments using an inhibitor revealed that Sema3A was required for AKT activation-mediated cellular growth and formation of cleft and bud in SMG rudiment culture. In addition, Wnt/β-catenin signaling decreased the Sema3A expression in the rudiment culture. ACC arising from salivary glands frequently exhibits malignant potential. Immunohistochemical analyses of tissue specimens obtained from 10 ACC patients showed that Sema3A was hardly observed in non-tumor regions but was strongly expressed in tumor lesions, especially in myoepithelial neoplastic cells, at high frequencies where phosphorylated AKT expression was frequently detected. These results suggest that the Sema3A-AKT axis promotes cell growth, thereby contributing to morphogenesis and pathogenesis, at least in ACC, of salivary glands.

ATR is a MYB regulated gene and potential therapeutic target in adenoid cystic carcinoma

Adenoid cystic carcinoma (ACC) is a rare cancer that preferentially occurs in the head and neck, breast, as well as in other sites. It is an aggressive cancer with high rates of recurrence and distant metastasis. Patients with advanced disease are generally incurable due to the lack of effective systemic therapies. Activation of the master transcriptional regulator MYB is the genomic hallmark of ACC. MYB activation occurs through chromosomal translocation, copy number gain or enhancer hijacking, and is the key driving event in the pathogenesis of ACC. However, the functional consequences of alternative mechanisms of MYB activation are still uncertain. Here, we show that overexpression of MYB or MYB-NFIB fusions leads to transformation of human glandular epithelial cells in vitro and results in analogous cellular and molecular consequences. MYB and MYB-NFIB expression led to increased cell proliferation and upregulation of genes involved in cell cycle control, DNA replication, and DNA repair. Notably, we identified the DNA-damage sensor kinase ATR, as a MYB downstream therapeutic target that is overexpressed in primary ACCs and ACC patient-derived xenografts (PDXs). Treatment with the clinical ATR kinase inhibitor VX-970 induced apoptosis in MYB-positive ACC cells and growth inhibition in ACC PDXs. To our knowledge, ATR is the first example of an actionable target downstream of MYB that could be further exploited for therapeutic opportunities in ACC patients. Our findings may also have implications for other types of neoplasms with activation of the MYB oncogene.

Adenoid cystic carcinoma: emerging role of translocations and gene fusions.

Adenoid cystic carcinoma (ACC), the second most common salivary gland malignancy, is notorious for poor prognosis, which reflects the propensity of ACC to progress to clinically advanced metastatic disease. Due to high long-term mortality and lack of effective systemic treatment, the slow-growing but aggressive ACC poses a particular challenge in head and neck oncology. Despite the advancements in cancer genomics, up until recently relatively few genetic alterations critical to the ACC development have been recognized. Although the specific chromosomal translocations resulting in MYB-NFIB fusions provide insight into the ACC pathogenesis and represent attractive diagnostic and therapeutic targets, their clinical significance is unclear, and a substantial subset of ACCs do not harbor the MYB-NFIB translocation. Strategies based on detection of newly described genetic events (such as MYB activating super-enhancer translocations and alterations affecting another member of MYB transcription factor family-MYBL1) offer new hope for improved risk assessment, therapeutic intervention and tumor surveillance. However, the impact of these approaches is still limited by an incomplete understanding of the ACC biology, and the manner by which these alterations initiate and drive ACC remains to be delineated. This manuscript summarizes the current status of gene fusions and other driver genetic alterations in ACC pathogenesis and discusses new therapeutic strategies stemming from the current research.

Adenoid cystic carcinoma: current therapy and potential therapeutic advances based on genomic profiling.

Adenoid cystic carcinoma (ACC) is a rare cancer with high potential for recurrence and metastasis. Efficacy of current treatment options, particularly for advanced disease, is very limited. Recent whole genome and exome sequencing has dramatically improved our understanding of ACC pathogenesis. A balanced translocation resulting in the MYB-NFIB fusion gene appears to be a fundamental signature of ACC. In addition, sequencing has identified a number of other driver genes mutated in downstream pathways common to other well-studied cancers. Overexpression of oncogenic proteins involved in cell growth, adhesion, cell cycle regulation, and angiogenesis are also present in ACC. Collectively, studies have identified genes and proteins for targeted, mechanism-based, therapies based on tumor phenotypes, as opposed to nonspecific cytotoxic agents. In addition, although few studies in ACC currently exist, immunotherapy may also hold promise. Better genetic understanding will enable treatment with novel targeted agents and initial exploration of immune-based therapies with the goal of improving outcomes for patients with ACC.

Expression and significance of notch signaling pathway in salivary adenoid cystic carcinoma

Notch signaling plays a role in stem cell biology, tumor formation, angiogenesis, and cell death. Targeting Notch pathway could serve as a therapeutic strategy in cancer. Little is known about the differential role of various components of the Notch pathway in salivary adenoid cystic carcinoma (AdCC). To investigate the association of the Notch pathway in AdCC carcinogenesis, we analyzed the Notch receptor (Notch-1, Notch-2, Notch-4) and Notch ligand (Jagged-1, Delta) expressions. The results showed elevated expression levels of all 5 proteins in AdCC tissue relative to normal salivary gland tissues. Jagged-1/Notch-2 coexpression was significantly associated with increased patient survival rate. The elevated expression level of these Notch receptors and ligands in AdCC points to Notch signaling as a key player in AdCC pathogenesis. Our data provide evidence for a relationship between Jagged-1/Notch-2 coexpression and better overall patient survival with AdCC. Targeting Notch signaling pathway may provide therapeutic benefits for these patients.

OP145: Salivary adenoid cystic carcinoma: Something out of notching?

Background Notch signaling evolves as an important mediator of stem cell biology, tumor formation, angiogenesis and cell fate decision. In mammals, there are four Notch receptors (Notch 1–4) and five ligands (Jagged-1 and -2, Delta-like (Dll)-1, -3 and -4). Dysregulation of Notch pathway has been found to play a crucial role in breast cancer oncogenesis and it could serve as a target for treatment. Relatively little is known about the pattern of expression of various components of Notch pathway in salivary adenoid cystic carcinoma (AdCC). To understand the role of Notch pathway in AdCC, we have undertaken a detailed expression analysis of various Notch receptors and their ligands in these tumors. Design Archival paraffin blocks of 199 AdCC were used and TMA were constructed. Immunohistochemical expression of Notch-1, Notch-2, Notch-4, Jagged-1, Delta were analyzed. Correlations between Notch receptors/ligands expression and clinical and histological parameters were assessed by Pearson’s Chi-square and M-L Chi-square tests; survival curves were generated with Kaplan–Meier method, statistical differences by log rank test. Results We found a general increase in the expression levels of Notch-1, Notch-2, Notch-4, Jagged-1, Delta proteins in AdCC, while weakly/undetectable levels in normal tissues. AdCC expressed the biomarkers as follow: 85% for Notch-1 (149/175) and Notch-4 (149/164), 80% for DLL1/Delta, 57% for Jagged 1 and 34% for Notch-2 (55/161). No significant statistical correlation was found between individual markers and clinico-pathological parameters. The combination of Jagged 1 and Notch 2 showed a significant p value (p 0.03644) for vital status at last contact within 12 years of presentation. Conclusions High expression of Notch receptors and ligands in AdCC places Notch signaling as a key player in AdCC pathogenesis. Our data provides the direct evidence for a relationship between Jagged-1/Notch-2 co-expression and better overall patient survival in AdCC. Targeting the Notch signaling pathway could provide therapeutic benefits.

Overexpression of macrophage migration inhibitory factor in adenoid cystic carcinoma: correlation with enhanced metastatic potential

Adenoid cystic carcinoma (ACC) is a malignant tumor frequently arising in salivary glands with poor long-term prognosis due to high rates of local recurrences and distant metastases. Macrophage migration inhibitory factor (MIF) is a multi-functional cytokine and has recently emerged as a pro-tumorigenic factor in various cancers. This study is designed to investigate the expression status and functional significance of MIF in ACC. Immunohistochemical staining was performed to evaluate the expression levels of MIF, HIF-1α, MMP-9, p53, and p-JNK in ACC tissues. In vitro, ACC-2 cells were exposed to recombinant human MIF (rMIF) or ISO-1 (an inhibitor of MIF) at different concentrations and times, followed by the detection of cell growth, viability, migration, and invasion, as well as the expression levels of several cellular signals. The immunohistochemical results demonstrated the overexpression of MIF in ACC tissues as well as its association with the distant metastasis. Further analyses showed a significant correlation between the staining of MIF and p-JNK. Moreover, the in vitro studies revealed that the treatment for ACC cells with ISO-1 significantly attenuated cell migratory and invasive capacity, as opposed to the limited promotive effects of rMIF. More importantly, MIF inhibition could cause the activation of JNK, correlating with the immunohistochemical findings on ACC tissues. The results suggest that MIF is likely to be an important player in the pathogenesis of ACC and may promote cancer metastasis, which possibly involves JNK inactivation. Further investigation of MIF-mediated molecular events may provide novel insights into the treatment for ACC.

Differential expression of c-kit and CD43 in histological subtypes of adenoid cystic carcinoma of salivary gland

Adenoid cystic carcinoma (ACC) of the salivary gland is characterized by a prolonged but inevitably unfavorable clinical course. Recent studies have suggested that the transmembrane tyrosine kinase receptor, c-kit proto-oncogene is involved in ACC pathogenesis. CD43 is a sialoglycoprotein that is typically expressed by hematopoietic cells and their derivative neoplasms, although positivity in epithelial tumors has only been recognized recently. The aim of this study was to evaluate c-kit and CD43 immunoreactivity in ACCs and to compare the extent of their expression in various histologically defined subgroups of ACC, and their probable involvement in ACC pathogenesis. Formalin-fixed paraffin-embedded sections from 35 ACCs were immunostained for c-kit and CD43 using monoclonal antibodies. Cytoplasmic and membranous c-kit immunoreactivity was detected in 25/35ACCs (71.4%) with strong immunostaining observed in solid pattern of ACC. Cytoplasmic and membranous CD43 immunoreactivity was detected in 18/35 (51.4%) of ACCs with strong immunostaining seen in the cribriform pattern. These results suggested that c-kit could be used as a prognostic marker for ACC and specific c-kit tyrosine kinase inhibitors such as imatinib, might be used in future therapeutic approaches against subgroups of ACC. CD43 appears to be preferentially expressed in salivary gland ACCs. Its expression decreased with cellular dedifferentiation and there was an inverse relationship between immunoexpression of c-kit and CD43 among ACC of salivary gland.

Identification of c-kit gene mutations in primary adenoid cystic carcinoma of the salivary gland

The CD117 (KIT) protein is overexpressed in many human neoplasms including adenoid cystic carcinoma of salivary glands. To evaluate the function of c-kit-activating mutations in adenoid cystic carcinoma of the salivary gland, we studied 14 cases (13 primary, 1 cervical lymph node metastasis) from our institution. KIT protein expression was evaluated by immunohistochemistry using formalin-fixed paraffin-embedded tissue. Mutational analyses of c-kit extracellular (exon 9), juxtamembrane (exon 11) and tyrosine kinase domains (exons 13 and 17) were performed by polymerase chain reaction, clonal selection and DNA sequencing. All 14 cases demonstrated strong KIT expression by immunohistochemistry. Molecular analysis was successful in 8 of 14 cases, and c-kit missense point mutations were detected in seven of eight cases (88%) including seven in exon 11, two in exon 9, two in exon 13 and two in exon 17. Eight silent point mutations were detected in five cases. Two cases contained missense mutations in more than one exon. Different mutations were found in the primary tumor and the cervical lymph node metastasis of one patient. Point mutations in domains similar to those described in gastrointestinal stromal tumors were detected, including Pro551Leu and Lys558Glu (5′ end of exon 11), Leu576Phe (3′ end of exon 11), Val643Ala (exon 13) and Asn822Ser (exon 17). Additional novel point mutations in exons 9, 11, 13 and 17 were also identified. This study is the first to report c-kit gene mutations in primary adenoid cystic carcinoma of the salivary gland. Identification of such potential gain-of-function mutations in exon 11, and less frequently in exons 9, 13 and 17, suggests that KIT may be involved in the pathogenesis of adenoid cystic carcinoma of salivary glands. Our study raises a prospect of correlation of c-kit mutation and a potential treatment of adenoid cystic carcinoma with tyrosine kinase inhibitor (imatinib).

Chromosome 6 deletion and candidate tumor suppressor genes in adenoid cystic carcinoma

As genomic deletion in chromosome 6 has been implicated in the pathogenesis of adenoid cystic carcinoma (ACC), we assayed 58 paired normal and tumor samples for loss of heterozygosity (LOH) using 38 microsatellite markers spanning chromosome 6. Genetic loss occurred in 57% of cases, with the greatest loss found within a 10 cM region flanked by markers D6S471 and D6S1687. Among the heterogeneous histologic subtypes of salivary gland carcinomas, only salivary duct carcinoma had a similar frequency of deletion in this region. This locus contains two major candidate tumor suppressor genes, PLAGL1 and LATS1. We analyzed the sequence of these genes in clinical samples of ACC, but found no tumor-specific mutations. Analysis of gene expression showed no substantial differences between samples of normal salivary gland and ACC, eliminating the most obvious candidate genes in this locus as tumor suppressors in ACC.

Differential KIT expression in histological subtypes of adenoid cystic carcinoma (ACC) of the salivary gland

Adenoid cystic carcinoma (ACC) of the salivary gland is characterized by a prolonged but inevitably unfavorable clinical course. Recent studies suggested the transmembrane tyrosine kinase KIT to be involved in ACC pathogenesis. To investigate KIT expression in histologically defined subgroups of ACC and to clarify whether KIT gene copy number gain contributes to KIT overexpression, tumor tissue microarray sections including 55 ACC tumors were analyzed by fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC). The prevalence of positive KIT immunostaining was 89% (49/55). Strong immunostaining of KIT was only found in cribriform and tubular but never in solid subtypes (p=0.02). Average KIT staining intensity was higher in cribriform and tubular (n=37) compared to solid (n=18) ACC subtypes (p=0.005). FISH analysis revealed copy number gains of the KIT gene in 6.1% (3/49) of tumors analyzed. Our results implicate that specific KIT tyrosine kinase inhibitors such as imatinib, might be used in future therapeutic approaches against subgroups of ACC.

Imatinib mesylate as treatment for adenoid cystic carcinoma of the salivary glands: Report of two successfully treated cases

Adenoid cystic carcinoma (ACC) is a malignant neoplasia of the salivary glands that is treated primarily by surgery. Local control and survival are usually compromised despite surgery. Expression of KIT tyrosine kinase is involved in the pathogenesis of ACC. Imatinib mesylate is a potent inhibitor of KIT tyrosine kinase, so we explored the possibility that ACC could be a potential target for this drug. We report two cases of unresectable ACC treated with imatinib mesylate in the context of recurrent disease (case 1) and locally advanced tumor at its initial presentation (case 2). Both patients responded well to treatment with imatinib mesylate. Significant regression of recurrent disease (case 1) resulted in a successful salvage surgical resection; the locally advanced tumor (case 2) had an excellent response to treatment, but, unfortunately, the patient refused salvage resection. This is the first time ACC is reported to respond to imatinib mesylate. Studies in which more patients are enrolled in controlled clinical trials are needed to confirm this observation.

Molecular differences in mucoepidermoid carcinoma and adenoid cystic carcinoma of the major salivary glands.

Mucoepidermoid carcinoma (MEC) and adenoid cystic carcinoma (ACC), the most common malignancies of the major salivary glands, are clinically and pathologically different. To determine whether MEC and ACC have different molecular characteristics, we examined the expression of erbB-2, erbB-3, epidermal growth factor receptor (EGFR), and transforming growth factor-alpha (TGF-alpha), important molecular features in other malignancies. Archival tissue sections of 22 MEC and 6 ACC tumors of the major salivary glands were evaluated immunohistochemically for expression of erbB-2, erbB-3, EGRF, and TGF-alpha. A differential immunostaining score, reflecting the difference in immunostaining between carcinoma and uninvolved salivary gland tissue, was calculated for cytoplasmic and membranous staining. Positive immunostaining for all biomarkers was observed in the cytoplasm and membrane of both tumors. However, expression was higher in MEC than in ACC tumors and was statistically significant for cytoplasmic EGFR (P =.009), TGF-alpha (P =.041), and membranous EGFR (P =.004). A significantly higher percentage of MEC cells also demonstrated positive immunostaining for cytoplasmic erbB-3 (P =.022), EGFR (P =.005), membranous erbB-3 (P =.022), and EGFR (P =.013). The differential immunostaining score was significantly higher for MEC compared with uninvolved alveolar tissue and the membranes of uninvolved ductal tissue. There were no statistically positive differential immunostaining scores for ACC. There is a clear difference in the molecular phenotypes of MEC and ACC. The lack of statistically significant expression in ACC, when compared with similar uninvolved salivary gland tissue, suggests minimal involvement for these molecular structures in the pathogenesis of ACC. Conversely, erbB-2, erbB-3, EGFR, and TGF-alpha may have a role in the development and progression of MEC. These results have therapeutic implications for MEC of the major salivary glands.