High-grade transformation of a polymorphous adenocarcinoma of the salivary gland: a case report and review of the literature

Background

Polymorphous adenocarcinoma (PAC) represents the second most widespread neoplasm of the minor salivary glands. These tumors rarely develop a histological progression from low-grade to high-grade malignancy, named "high-grade transformation" (HGT). Only nine cases are described in literature.

Case description

Here, we describe the case of a 76-year-old male patient with a PAC recurrence of the oral floor displaying HGT, and we explore the tumor cytomorphological features, genomic profiling, and the patient's clinical management. The tumor mass was characterized by poorly atypical cellular elements with vesicular nuclei and comedonecrosis foci. The growth pattern was predominantly solid, tubular, and cribriform. The lesion did not show microsatellite instability or targeted molecular alterations. The case was successfully treated with radical surgery followed by radiotherapy.

Conclusion

We report for the first time the recurrence of a PAC with HGT arising in the oral floor after 20 years from the primary lesion. These preliminary data and the literature analysis enhance the knowledge of this extremely rare disease.

[Why is the histomorphological diagnosis of small salivary gland tumours so much more difficult?]

There is a widespread impression among clinicians and pathologists that the histomorphological diagnosis of minor salivary gland tumours is more difficult and more frequently misdiagnosed than that of major glands. This is based on subjective clinical impression; scientific proof of and potential reasons for this difference are lacking. We identified 14 putative clinical, histopathological and combined clinical-histological reasons and four consequences, which together could explain the perceived greater difficulty of diagnosing minor gland tumours. We performed a thorough literature search and a statistical comparison of data from a personal large consultation series (biased for "difficult" cases) with cumulated data from a routine, unselected (non-consultation) series from the literature. Through this comparison, we could prove with statistical significance a series of reasons and consequences for this greater diagnostic difficulty in minor glands. Frequent incisional biopsies, almost obligatory low-grade bland cytology in malignant tumours and insufficient clinical-pathological communication emerged as the most important reasons. The special anatomic location of the hard palate contributes to further diagnostic difficulties, such as tumour necrosis, mucosal ulceration, pseudoinvasion and the "tumoural-mucosal fusion" phenomenon. Knowledge of these pitfalls in clinic and pathology can help overcome these difficulties and reduce the misdiagnosis rate in minor gland tumours. Our findings result in a series of recommendations both for the clinic and pathology.

Epiglottic Polymorphous Adenocarcinoma With Multiple Bone Metastases Detected by 68Ga-FAPI PET/CT

ABSTRACT

Polymorphous adenocarcinoma (PAC) is generally an indolent tumor that mostly commonly affects the minor salivary gland. Polymorphous adenocarcinoma with distant metastases is extremely rare. In this case, we reported 18F-FDG and 68Ga-FAPI PET/CT imaging findings in a rare case of epiglottic PAC with multiple bone metastases. 68Ga-FAPI PET/CT showed superiority over 18F-FDG PET/CT for detecting the primary and metastatic PAC. This case highlighted that 68Ga-FAPI may be a promising radiopharmaceutical in the diagnosis of PAC, especially for detecting the PACs arising in uncommon sites.

Why is the histomorphological diagnosis of tumours of minor salivary glands much more difficult?

AIMS

There is a widespread perception among clinicians and pathologists that the histomorphological assessment of minor salivary gland (MinSG) tumours is more difficult and hampered by more misdiagnoses than that of major salivary gland tumours. This is based on a vague, subjective clinical impression, lacking scientific proof. The aim of the present study was to identify and statistically verify potential reasons that could explain this difference.

METHODS AND RESULTS

We identified 14 putative clinical, pathological and combined clinicopathological reasons that, altogether, could explain the phenomenon of the perceived greater diagnostic difficulty associated with MinSG tumours. We performed a comprehensive literature search and a statistical comparison of data from a large personal consultation series (biased for difficult cases) with cumulated data from straightforward, unselected (non-consultation) series from the literature. By performing this comparison, we identified, with statistical significance, a comprehensive series of reasons, as well as of consequences, of the greater difficulty in diagnosing MinSG tumours.

CONCLUSIONS

Among the 14 criteria, high frequencies of initial incisional biopsies and of a low-grade category in malignant tumours emerged as the two most important reasons for enhanced diagnostic difficulty. Very rare entities, unusual locations, shortcomings in clinicopathological communication, and pecularities of the special anatomical location of the hard palate, such as tumour necrosis, mucosal ulceration, pseudoinvasion, and the peculiar phenomenon of 'tumoral-mucosal fusion', contribute to further diagnostic difficulties. The awareness of these shortcomings and pitfalls enables us to provide a series of recommendations for clinicians and pathologists that might aid in assessment and reduce the rate of misdiagnosis of MinSG tumours.

Molecular and Cellular Modelling of Salivary Gland Tumors Open New Landscapes in Diagnosis and Treatment

Salivary gland tumors are neoplasms affecting the major and minor salivary glands of the oral cavity. Their complex pathological appearance and overlapping morphological features between subtypes, pose major challenges in the identification, classification, and staging of the tumor. Recently developed techniques of three-dimensional culture and organotypic modelling provide useful platforms for the clinical and biological characterization of these malignancies. Additionally, new advances in genetic and molecular screenings allow precise diagnosis and monitoring of tumor progression. Finally, novel therapeutic tools with increased efficiency and accuracy are emerging. In this review, we summarize the most common salivary gland neoplasms and provide an overview of the state-of-the-art tools to model, diagnose, and treat salivary gland tumors.

Salivary ghost cell carcinoma: case report and proposal of a new entity

Various topographically heterogeneous, histologically related groups of basaloid tumours are characterized by ghost cell differentiation with associated CTNNB1 mutations and nuclear β-catenin expression. We describe the unique case of a malignant tumour with ghost cell differentiation in the floor of the mouth, in which clinical, radiological, histological, immunohistological and molecular data altogether strongly indicate classification as a new type of salivary gland carcinoma.

Polymorphous adenocarcinoma of the salivary glands: reappraisal and update

Although relatively rare, polymorphous adenocarcinoma (PAC) is likely the second most common malignancy of the minor salivary glands (MiSG). The diagnosis is mainly based on an incisional biopsy. The optimal treatment comprises wide surgical excision, often with adjuvant radiotherapy. In general, PAC has a good prognosis. Previously, PAC was referred to as polymorphous low-grade adenocarcinoma (PLGA), but the new WHO classification of salivary gland tumours has also included under the PAC subheading, the so-called cribriform adenocarcinoma of minor salivary glands (CAMSG). This approach raised controversy, predominantly because of possible differences in clinical behaviour. For example, PLGA (PAC, classical variant) only rarely metastasizes, whereas CAMSG  often shows metastases to the neck lymph nodes. Given the controversy, this review reappraises the definition, epidemiology, clinical presentation, diagnostic work-up, genetics, treatment modalities, and prognosis of PAC of the salivary glands with a particular focus on contrasting differences with CAMSG.

Palatal Polymorphous Adenocarcinoma with High-Grade Transformation: A Case Report and Literature Review

Polymorphous adenocarcinoma (PAC) is the second most common intraoral malignant neoplasm of the minor salivary glands. However, it is very rare for PAC to show high-grade transformation (HGT) and to our knowledge, the English literature only seven reported cases. HGT tends to be observed when PAC recurs, and it is extremely rare to be seen at initial presentation. Here we report a 43-year-old Japanese male patient with PAC of the right palate showing HGT at initial presentation. Histopathologically, the tumor was characterized by a prominent solid and papillary-cystic growth pattern, with nuclear atypia and necrosis in area of HGT. The immunohistochemical staining pattern was consistent with PAC, as the tumor cells showed diffuse positivity for cytokeratin, vimentin and S-100, and focal positivity for bcl-2, ɑ-SMA and EMA. The tumor cells in HGT areas were markedly positive for AR and Ki-67 (about 40%/HPF), and also focally positive for cyclin D1 and p53, whereas HER2/neu, ER, PgR, p63, D2-40, GCDFP-15, and mitochondria were negative. Here we present a very rare case of palatal PAC with HGT at initial presentation.