Polymorphous low-grade adenocarcinoma versus pleomorphic adenoma of minor salivary glands: resolution of a diagnostic dilemma by immunohistochemical analysis with glial fibrillary acidic protein

Diagnostic role of DOG-1, GFAP and B-catenin in Basal cell Adenoma and Cellular Pleomorphic Adenoma of the Salivary Gland

BACKGROUND

Pleomorphic Adenoma (PA) and Basal cell adenoma (BCA) are benign salivary gland tumors that may pose a diagnostic challenge if typical features are not present. Due to the increased relapse and malignant transformation rate of the former, a correct diagnosis carries relevant prognostic information. Even though immunohistochemistry (IHC) plays a limited role in the diagnosis of these tumors, the use of IHC panels could increase diagnostic accuracy. In the present work, we aimed to demonstrate that the use of an IHC panel consisting of Glial Fibrillary Acid Protein (GFAP), B-Catenin and Discovered On GIST 1 (DOG-1) can aid in the differential diagnosis between PA and BCA.

METHODS

We analyzed 18 cases of benign salivary gland tumors (Pleomorphic adenomas and Basal cell adenomas) with overlapping histologic features. First, a head and neck pathologist diagnosed the cases relying on morphology alone. Afterwards, cases were re-evaluated considering the IHC panel results. Inter-observer IHC scoring concordance was evaluated with pre-defined marker cut-off points using Cohen's Kappa scores.

RESULTS

Based on morphology alone, 9 cases were classified as PA while the remaining tumors were considered to be BCA. Five out of nine BCA cases showed GFAP staining and absent nuclear B-catenin and DOG-1 positivity. Conversely, 2 PA cases showed absent GFAP and positive nuclear B-catenin with concurrent DOG-1 expression. Therefore, after IHC evaluation, up to 40% of morphologic diagnoses were reconsidered. Overall, the inter-observer concordance for IHC evaluation was good (resulting Kappa Scores between 0.78 and 1).

CONCLUSION

Our work supports the use of a concise IHC panel to improve the diagnostic accuracy of benign salivary gland tumors with overlapping histologic features.

Immunohistochemical Profile of Polymorphous Adenocarcinoma of Minor Salivary Gland: A Systematic Review and Meta-Analysis

Polymorphous adenocarcinoma (PAC) is a rare variant of minor salivary gland tumors. Because of its architectural diversity, histological diagnosis of PAC can be difficult especially for small biopsies, and immunohistochemistry is of great help in differentiating it from its histologic mimics. The aim of this study is to conduct a systematic literature review to identify reliable immunohistochemical markers for PAC. We conducted an electronic literature search of the MEDLINE, ScienceDirect, SpringerLink, and Wiley Online Library databases, covering the literature published in the period between 1988 and 2021. The eligibility criteria included case reports and retrospective studies of PAC cases with details of immunohistochemical markers. Following the search and selection process, 32 studies with 409 cases were included in this systematic review. Overall, > 90% positivity was observed for pan-cytokeratin (CK) (97.3%), CK7 (96.8%), CK7/8 (97.4%), E-cadherin (90.0%), Vimentin (92.5%), S100 (97.0%), p63 (91.7%), and SOX10 (100%), while little to no positivity was observed for CK20 (0.0%), p40 (0.0%), and GFAP (5.0%). The average MIB-1 labeling index was 3.78%. The results of this systematic review indicate that CK7+/CK20-, p63+/p40-, S100+, Vimentin+, and GFAP- immunophenotype have diagnostic value for PAC. In addition, the use of S100, MSA, p40, and c-Kit provide additional layers of information helpful to differentiate PAC from adenoid cystic carcinoma, one of challenging differential diagnoses.

Salivary GFAP as a potential biomarker for diagnosis of mild cognitive impairment and Alzheimer's disease and its correlation with neuroinflammation and apoptosis

Glial fibrillary acidic protein (GFAP) is the main constituent of the astrocytic cytoskeleton, overexpressed during reactive astrogliosis-a hallmark of Alzheimer's Disease (AD). GFAP and established biomarkers of neurodegeneration, inflammation, and apoptosis have been determined in the saliva of amnestic-single-domain Mild Cognitive Impairment (MCI) (Ν = 20), AD (Ν = 20) patients, and cognitively healthy Controls (Ν = 20). Salivary GFAP levels were found significantly decreased in MCI and AD patients and were proven an excellent biomarker for discriminating Controls from MCI or AD patients. GFAP levels correlate with studied biomarkers and Aβ₄₂, IL-1β, and caspase-8 are its main predictors.

Polymorphous adenocarcinoma: A case report along with its characteristics and diagnostic challenges

Polymorphous adenocarcinoma (PAC) is an uncommon tumor that affects minor salivary glands mainly. It presents as an indolent malignancy that frequently manifests as an asymptomatic, slow-growing mass within the oral cavity, especially palate and its clinical behavior resembles that of benign neoplasm, often causing delay in the diagnosis. Here, we report a rare case of PAC of palate in a 49-year-old female patient along with a concise review of characteristics of PAC and highlight diagnostic challenges caused by the overlap of clinical and microscopic features between PAC, pleomorphic adenoma and adenoid cystic carcinoma.

Role of Antioxidants in Minor Salivary Glands Cancer in the Elderly

BACKGROUND

Minor salivary gland tumors (MSGTs) are infrequent, representing 10% to 15% of all salivary neoplasms. Despite this low frequency, a significant increase in the incidence of these tumors has been reported in the lasts 30 years. While tumors of the salivary glands can appear at any age, different authors consider the peak of incidence to be associated with old age (60+). The etiopathogenesis of MSGTs remains unclear. In this context, the aim of this study was to explore the hypothesis that age-related changes in salivary antioxidant capacity are involved in the pathogenesis of minor salivary glands tumors to identify possible preventive measures.Furthermore the study aimed to describe the clinico-pathological features of a multi-institutional case series of MSGTs which results are consistent with data in the literature.

METHODS

An electronic search of the English language literature was performed using PubMed and Google scholar (<scholar.google.com>). Databases were screened for papers using a number of search strings constructed using relevant terms (minor salivary glands tumors, elderly, diet, antioxidant, saliva, salivary glands).

RESULTS

According to the world literature, the peak of incidence of MSGTs is between the fifth and seventh decades of life. To date, the only confirmed risk factor for salivary gland tumors is the exposure to ionizing radiation. The significantly reduced salivary antioxidant capacity in old people may explain the higher prevalence of these tumors in the elderly population.

CONCLUSIONS

Further investigation is required to determine the real etiopathogenesis of MSGTs and why these tumors result more frequent in elderly patients.

Pleomorphic Adenoma of Soft Palate: Unusual Occurrence of the Major Tumor in Minor Salivary Gland-A Case Report and Literature Review

Salivary gland tumours constitute about less than 4 % of all head and neck tumours. Pleomorphic adenoma, also called benign mixed tumour, is the most common tumour of the salivary glands. About 80-90 % of these tumours occur in the major salivary glands mainly parotid gland and 10 % of them occur in the minor salivary glands. The most common site for pleomorphic adenoma of the minor salivary glands is the palate, followed by the lips and the cheeks. Other rare sites include the floor of the mouth, tongue, tonsil, pharynx, retromolar area and the nasal cavity. Here, we are reporting a case of pleomorphic adenoma of the minor salivary glands of the soft palate in a 36-year-old Indian female. The mass was removed by wide local excision with adequate margins under general anesthesia. There was no recurrence seen after a follow-up period of 1 year.

Polymorphous low grade adenocarcinoma

Polymorphous low-grade adenocarcinoma (PLGA), is a rare, salivary gland intraoral tumor with complexities in diagnosis and this review highlights the difficulties.

Review and Updates of Immunohistochemistry in Selected Salivary Gland and Head and Neck Tumors

Context

Immunohistochemistry is a useful tool for diagnosing salivary gland and head and neck tumors.

Objective

To review immunohistochemical markers, which can aid in the diagnosis of selected salivary gland and head and neck tumors.

Data Sources

Literature review and authors' personal practice experience.

Conclusions

Salivary gland and head and neck tumors include a large diverse group of tumors with complex and overlapping histologic features. Immunohistochemistry plays an important role in resolving the differential diagnosis of some salivary gland and head and neck tumors and can provide information for the prognosis of certain tumors.

Surface Papillary Epithelial Hyperplasia (Rough Mucosa) is a Helpful Clue for Identification of Polymorphous Low-Grade Adenocarcinoma

The purpose of this study is to evaluate surface papillary epithelial hyperplasia, a microscopic finding that corresponds to the clinical finding of rough or stippled mucosa, as a predictor of polymorphous low-grade adenocarcinoma (PLGA). We conducted a retrospective review of minor salivary gland neoplasms submitted to our biopsy service from 1991 to 2013. Our review was limited to lesions involving the oral cavity/soft palate with the following diagnoses: PLGA, pleomorphic adenoma (PA), mucoepidermoid carcinoma (MEC), and adenoid cystic carcinoma (ACC). A total of 202 minor salivary gland neoplasms were included in the study. Among cases in which surface epithelium was present for evaluation (n = 112), surface papillary epithelial hyperplasia was evident in 30 % of PLGA and 1 % of non-PLGA (i.e., MEC, ACC, PA). The greater frequency of surface papillary epithelial hyperplasia in the PLGA versus non-PLGA cases and in the benign versus malignant cases was significant (p = .0001 and p = .041, respectively). The sensitivity and specificity of papillary epithelial hyperplasia for PLGA were 30 % (95 % confidence interval (CI) 11.97-54.27 %) and 99 % (95 % CI 94-99.82 %), respectively. The clinical presentation of PLGA appeared relatively nonspecific, with all analyzed tumor types exhibiting a predilection for females, middle-aged to older adults, palatal location, pink/tan/normal color, and firm consistency. In conclusion, papillary epithelial hyperplasia was evident in only a minority of PLGA. However, when present within the context of a palatal salivary gland neoplasm, it appears to indicate a high probability of PLGA. Accordingly, rough mucosa may be a useful clinical pearl for identification of PLGA.

Polymorphous low grade adenocarcinoma has a consistent p63+/p40- immunophenotype that helps distinguish it from adenoid cystic carcinoma and cellular pleomorphic adenoma

Polymorphous low grade adenocarcinoma (PLGA) is a tumor of minor salivary glands that exhibits considerable morphologic overlap with adenoid cystic carcinoma and cellular pleomorphic adenoma, especially in small biopsy specimens. Unlike these other tumor types. PLGAs do not harbor a myoepithelial component, yet their frequent positivity for p63 diminishes the usefulness of this particular myoepithelial marker as a discriminating immunostain. p40 is an antibody that recognizes ΔNp63, a p63 isoform that is more specific for true myoepithelial differentiation. As such, p40 immunostaining could help distinguish PLGAs from adenoid cystic carcinomas and pleomorphic adenomas. In this study, p63 and p40 immunohistochemistry was performed on paraffin embedded, formalin fixed tissue from 11 PLGAs, 101 adenoid cystic carcinomas, and 31 pleomorphic adenomas. All 11 PLGAs (100 %) were positive for p63 but completely negative for p40. Among adenoid cystic carcinomas, 91 of 101 (90 %) were positive for p63 and 90/101 (89 %) were positive for p40. The single discordant p63+/p40- adenoid cystic carcinoma exhibited solid architecture and high grade features not typically seen in PLGA. Among pleomorphic adenomas, 21/31 (68 %) were positive for p63 and 13/31 (42 %) were positive for p40. For the pleomorphic adenomas, the discordant p63+/p40- staining pattern was seen only in the overtly mesenchymal chondromyxoid stroma. The cellular epithelial component of the pleomorphic adenomas demonstrated concordant p63+/p40+ or p63-/p40- immunophenotypes. PLGA consistently exhibits a p63+/p40- immunophenotype that can help distinguish it from adenoid cystic carcinoma and cellular pleomorphic adenoma, tumors that characteristically demonstrate concordant p63 and p40 immunostaining patterns. A p63/p40 immunohistochemical panel can provide a valuable tool for making the distinction between these morphologically similar but clinically divergent entities.

Takahashi R, Nagai T, Yoshida M, Suzuki F, Obikane H, Yamashina M, Matsubayashi J. Immunohistochemical analysis of salivary gland tumors: application for surgical pathology practice

Salivary gland tumors are relatively uncommon and there exists a considerable diagnostic difficulty owing to their diverse histological features in individual lesions and the presence of a number of types and variants, in addition to overlapping histological patterns similar to those observed in different tumor entities. The classification is complex, but is closely relevant to the prognostic and therapeutic aspects. Although hematoxylin-eosin staining is still the gold standard method used for the diagnosis, immunohistochemistry (IHC) can enhance the accuracy and be a helpful tool when in cases to investigate the subjects that cannot be assessed by histological examination, such as the cell nature and differentiation status, cell proliferation, and tumor protein expression. This review depicts on the practical diagnostic utility of IHC in salivary gland tumor pathology under the following issues: assessment of cell differentiation, focusing on neoplastic myoepithelial cells; discrimination of histologically mimic tumor groups; diagnosis of specific tumor types, e.g., pleomorphic adenoma, adenoid cystic carcinoma, and salivary duct carcinoma; and evaluation of malignancy and prognostic factors. IHC plays a limited, even though important, role in the diagnosis of salivary gland tumors, but is often useful to support the histological assessment. However, unfortunately few tumor type-specific markers are still currently available. For these reasons, IHC should be considered a method that can be used to assist the final diagnosis, and its results themselves do not directly indicate a definitive diagnosis.

Glial fibrillary acidic protein in tumor types with cartilaginous differentiation

Glial fibrillary acidic protein (GFAP) is a member of the intermediary filament protein family. It is an important component of astrocytes and a known diagnostic marker of glial differentiation. GFAP is expressed in other neural tumors and pleomorphic adenoma and, less frequently, in cartilage tumors, chordomas, and soft tissue myoepitheliomas. The aim of this study was to evaluate the role of GFAP and its reliability in nonglial tumors as an immunohistochemical marker. We evaluated GFAP gene and protein expression using Q-PCR and immunohistochemistry, respectively, in 81 and 387 cases of soft tissue, bone tumors, and salivary pleomorphic adenomas. Immunohistochemistry staining for GFAP was observed in all osteosarcomas (8 cases), all pleomorphic adenomas (7 cases), in 5 of 6 soft tissue myoepitheliomas, and in 21 of 76 chondrosarcomas. By Q-PCR, GFAP was highly expressed in pleomorphic adenomas and, to a lesser extent, chondrosarcomas, soft tissue myoepitheliomas, and chondroblastic osteosarcomas. The results that we obtained by immunohistochemistry and Q-PCR were well correlated. GFAP is a potential marker for tumors with cartilaginous differentiation, supported by evidence that GFAP is expressed in certain cases of myoepithelial tumors by immunohistochemistry, including soft tissue myoepitheliomas, which are related to cartilaginous differentiation. These findings contribute significantly to the diagnosis of soft tissue myoepitheliomas with cartilaginous differentiation and chondroblastic osteosarcoma in mesenchymal tumors.

Polymorphous low-grade adenocarcinoma: a review regarding an unusual presentation as infected odontogenic cyst

The World Health Organisation (WHO) classified polymorphous low-grade adenocarcinoma (PLGA) in 1990 as a low-grade malignancy; ICD-O 8525/3 being the assigned international code. It has been frequently described as occurring in hard- or soft-palate accessory salivary glands: some cases being described in the tongue and in major salivary glands. We present an extensive literature review about PLGA and the most common diagnostic pitfalls. We also report the first case where it was seen surrounding an impacted maxillary tooth and discuss it in regard to our review.

[Polymorphous low-grade adenocarcinoma: a palatine and a labial location]

INTRODUCTION

Polymorphous low-grade adenocarcinoma (PLGA) is a variant of malignant tumor of minor salivary glands. We had for aim to discuss morphology, evolution and differential diagnosis of this rare tumor.

CASE REPORTS

The first case was a 65-year-old woman admitted for a two-month history of a right submaxillary swelling. The examination revealed a tumor of the right side of the palate. Biopsy was positive for a pleomorphic adenoma. The mass was enlarged and surgical resection was performed. The diagnosis was a partially resected PLGA. The patient also received adjuvant radiotherapy. There was a local recurrence 28 months after complete treatment. The second case was a 57-year-old woman who consulted for a 12-year history of lower lip swelling. The examination revealed a painless 2cm long located nodule in the mucosal side of the lower lip. An excisional biopsy was performed. The pathological examination concluded to a completely resected PLGA. The patient was free of disease at 54 months follow-up.

DISCUSSION

The morphologic diversity and cytological uniformity of PLGA may make the differential diagnostic difficult especially with adenoid cystic carcinoma and pleomorphic adenoma. Its aggressiveness is proved by a local infiltrative growth pattern requiring a large surgical excision.

Distinctive pattern of glial fibrillary acidic protein immunoreactivity useful in distinguishing fragmented pleomorphic adenoma, canalicular adenoma and polymorphous low grade adenocarcinoma of minor salivary glands

OBJECTIVES

Immunohistochemistry (IHC) can be helpful in the diagnosis of minor salivary gland neoplasms including those that have been incisionally biopsied or fragmented during surgery that do not contain key diagnostic features on hematoxylin and eosin sections. IHC has been used as an adjunct to distinguish among many salivary gland neoplasms using both qualitative and quantitative methods. The objective of this study was to determine whether a distinctive immunoreactivity staining pattern to GFAP can be consistently observed among three selected minor salivary gland neoplasms and thus serve as a diagnostic adjunctive procedure.

STUDY DESIGN

Glial fibrillary acidic protein (GFAP) reactivity was examined among 78 minor salivary gland neoplasms: 27 canalicular adenomas (CAA), 21 pleomorphic adenomas (PA) and 30 polymorphous low grade adenocarcinomas (PLGA). Each case was evaluated by two oral and maxillofacial pathologists (OMP) blinded to the diagnosis. Consensus was reached on the pattern of GFAP reactivity among the neoplastic cells and on the similarities and differences among the cases.

RESULTS

Ninety-six percent (96%) of CAAs demonstrated a distinctive linear immunoreactive pattern among cells in proximity to connective tissue interface. All (100%) PAs demonstrated diffuse immunopositivity within tumor cells. All (100%) PLGAs showed little or no intralesional reactivity and no peripheral linear immunoreactivity. Additional challenge cases were examined by outside OMPs to demonstrate the utility of these findings.

CONCLUSIONS

This study demonstrates that the pattern of GFAP immunoreactivity may be an adjunct to diagnosis among PA, CAA and PLGA. The pattern of distinctly linear GFAP immunoreactivity at the tumor/connective tissue interface in CAA has not been reported previously. This distinctive feature may permit the pathologist to differentiate among CAA, PA and PLGA when an incisional biopsy and/or fragmentation cause key diagnostic features to be absent. Because each of these neoplasms requires a different treatment approach, this can be of major significance.

Polymorphous low grade adenocarcinoma presenting an uncommon radiographic aspect

The aim of this study was to present clinical, histological and immunohistochemical aspects of a polymorphous low grade adenocarcinoma occurring in the mandible. A radiolucent tumour, located in the right mandible, was removed from a 40-year-old woman. Radiographic and CT exams revealed that the lesion expanded bucco-lingual cortical plates and presented an irregular scalloping of the bone. The surrounding lining mucosa was intact. The patient underwent total surgical removal of the lesion with an intraoperative biopsy. Histological diagnosis was polymorphous low-grade adenocarcinoma confirmed by immunohistochemical study. One-year follow up was uneventful. The accurate diagnosis of lesions presenting unusual clinical aspects, as the one presented here, is critical for correctly handling treatment.

Polymorphous low-grade adenocarcinoma of the palate

OBJECTIVE

Polymorphous low-grade adenocarcinoma (PLGA) is a rare tumor that mostly affects minor salivary glands. The purpose of this study is to report six new cases followed-up during a long period. We also review the literature concerning clinical, histological and immunohistochemical features, as well as the proper management.

METHODS

Malignant tumors of the salivary glands diagnosed in our department from 1990 to 1999 were reviewed. A total of 66 cases were registered. Six of these cases were diagnosed as PLGA. All cases satisfied the histopathological criteria for this entity, and at least 3 years follow-up was available.

RESULTS

In the six cases the primary location was the mucosa of the palate. Hard palate was affected in 83.3% of the cases. There were no cases of extraoral PLGA in our series. Tumors were ulcerated in a 16.6% of the cases, and exofitic in the other 86.4%. Histologically, it was observed a tumoral proliferation of round clusters of uniform cells with round-to-oval clear nuclei and small nucleoli. All the cases underwent surgical management with local excision with surgical margins, five of them with bone extirpation associated. No recurrence was observed in four cases, whereas the remaining two cases showed recurrence in the follow-up. In one of the patients, lococervical recurrence appeared 12 months after the surgery, and this patient died after a few months. The remaining patients have been followed-up for 11, 7, 4 and 3 years postoperatively, with no evidence of recurrence.

CONCLUSION

Our results for a long follow-up period support the idea for a low grade of malignancy and good prognosis of this tumor, but the appearance of recurrences many years after the surgery must induce us to be very careful and systematic with the follow-up.

Differential diagnosis between adenoid cystic carcinoma and pleomorphic adenoma of the minor salivary glands of palate

Tumors arising from minor salivary glands of the palate may exhibit an overlap of clinical and biologic features that may produce diagnostic and therapeutic dilemmas. Surgical treatment can be very different, depending on the dimensions and malignant or benign nature of the tumors, and therefore should be planned on the basis of an accurate differential diagnosis. A retrospective analysis in 24 patients with pleomorphic adenoma and adenoid cystic carcinoma of minor salivary glands of the palate was performed to investigate the accuracy of fine needle aspiration cytology (FNAC) and biopsy with histology in the preoperative diagnosis. Preoperative diagnoses obtained with FNAC and biopsy were compared with findings of the definitive histopathologic examination performed on the resected mass. Correspondence between the preoperative diagnoses determined by FNACs and the definitive histopathologic results was observed in 22 of 24 cases, whereas a complete equivalence was found with regards to histology. In the analysis, FNAC was associated with 91.6% accuracy and an error rate of 8.4% in the diagnosis of pleomorphic adenoma and adenoid cystic carcinoma of the palate. From the results of the analysis, histologic examination is still the most accurate diagnostic tool in such tumors. FNAC can be considered in tumors of the head and neck regions that are difficult to reach by means of a common biopsy.

Malignant Chondroid Syringoma with Bone Invasion: A Case Report and Review of the Literature

We describe a 27-year-old Japanese female with a recurrent nodule on the left big toe and local bone invasion. Histopathologically, the tumor consisted of nests of atypical cells with few mitotic cells, which partly formed gland-like structures. Areas of myxoid degeneration, positive for Alcian blue staining and that did not stain after they were digested with hyaluronidase, were prominent in the matrix among tumor cells. Positive staining was noted in tumor cells for cytokeratin (AE1+AE3), S-100 protein, neuron specific enolase (NSE), and glial fibrillary acidic protein (GFAP). These findings, especially positive GFAP staining were characteristic and very helpful for the diagnosis of the rare tumor-malignant chondroid syringoma. Based on the previous reports, 39% of cases were found to have metastatic lesions and 22% died of this malignant tumor. There have been no reports reporting effectiveness of chemotherapy and radiotherapy, and an early wide excision with a broad margin may be the most reliable treatment to date.

C-kit expression in the salivary gland neoplasms adenoid cystic carcinoma, polymorphous low-grade adenocarcinoma, and monomorphic adenoma

OBJECTIVE

Differentiating between adenoid cystic carcinomas (ACCs), polymorphous low-grade adenocarcinomas (PLGAs), and the monomorphic adenomas (including canalicular adenomas, trabecular adenomas, and basal cell adenomas) can present a diagnostic challenge, especially when examining tissue obtained from small incisional or fragmented biopsies. Recent studies have revealed that overexpression of the tyrosine kinase receptor protein c-kit occurs in a narrow subset of malignant neoplasms, including gastrointestinal stromal tumors, myeloid leukemias, seminomas, and ACCs. C-kit reportedly is not expressed in PLGAs. We compared the expression of the c-kit antigen in the malignant salivary gland neoplasms ACC and PLGA with its expression in salivary gland monomorphic adenoma (including canalicular adenoma and basal cell adenoma).

STUDY DESIGN

Formalin-fixed paraffin-embedded sections of 49 salivary gland neoplasms (17 monomorphic adenomas, 17 PLGAs, and 15 ACCs) accessioned between 1989 and 2002 were retrieved from the files of the Department of Pathology, Long Island Jewish Medical Center, and were stained with an anti-c-kit polyclonal antibody.

RESULTS

C-kit reactivity was uniformly positive in the cytoplasm of luminal neoplastic cells in ACCs (15/15, 100%). Positive reactivity was also identified in the majority of PLGAs (16/17, 94%), with at least 25% of the tumor cells being positive. Similar reactivity was seen in monomorphic adenomas (16/17, 94%).

CONCLUSIONS

In contrast to previous reports, we find that c-kit expression was not restricted to ACC but was expressed in all 3 tumor types evaluated (ACC, PLGA, and monomorphic adenoma). Therefore, c-kit does not appear to be a useful marker for distinguishing between either ACC and PLGA in equivocal cases, or in benign and malignant salivary gland neoplasms.

Salivary gland tumours

Salivary gland tumours are a relatively rare and morphologically diverse group of lesions. Although most clinicians and pathologists will have encountered the more common benign neoplasms, few have experience of the full range of salivary cancers, which are best managed in specialist centres. This review considers some current areas of difficulty and controversy in the diagnosis and management of these neoplasms. The classification of these lesions is complex, encompassing nearly 40 different entities, but precise classification and terminology is essential for an accurate diagnosis and for the allocation of tumours to prognostic groups. For many salivary tumours diagnosis is straightforward but the wide range of morphological diversity between and within tumour types means that a diagnosis may not be possible on small incisional biopsies and careful consideration of the clinical and pathological features together is essential. Although tumour grading is important and helpful, it is not an independent prognostic indicator and must be considered in the context of stage. Large malignancies tend to have a poor prognosis regardless of grade and even high-grade neoplasms may do well when they are small. A helpful guide to management of salivary cancers is the '4 cm rule'.