Peculiar nuclear atypia associated with MDM2 gene amplification in carcinoma ex-pleomorphic adenoma harbouring an alteration of HMGA2

AIMS

Salivary gland neoplasms (SGN) exhibiting the HMGA2::WIF1 fusion are recognized by their resemblance to histology found in canalicular adenoma. Recently, ~20% of cases among 28 HMGA2::WIF1-rearranged-SGN showed malignancy and adverse outcomes (recurrence, distant metastasis, and disease-specific mortality). Among them, MDM2/CDK4 amplifications were identified in one case. This outcome suggests that the MDM2/CDK4 amplifications could be useful to predict an aggressive course of carcinoma ex-pleomorphic adenoma (CEPA).

METHODS AND RESULTS

We investigated the correlation between HMGA2 fusion and MDM2 amplification in four salivary gland neoplasms, providing detailed clinicopathological features and outcomes. Cases were selected from different institutions. Histological examination, immunohistochemistry, fluorescence in situ hybridization (FISH), RNA sequencing, and whole-exome capture were performed. The cohort included four CEPA cases, all female, aged between 32 and 89 years. Tumours arose from the parotid gland with an average size of 24.5 mm. None exhibited recurrence or distant metastases during the 4-5 months of follow-up. Pathologically, all cases displayed a peculiar atypical nuclei with 'gear-like appearance'. Immunohistochemically, tumours exhibited a biphasic pattern with myoepithelial and ductal differentiation markers. All cases showed HMGA2 overexpression and MDM2 amplification by FISH and RNA sequencing. In a control cohort of MDM2 nonamplified CEPA cases, not exhibiting the peculiar nuclear atypia.

CONCLUSIONS

Our findings suggest a strong correlation between HMGA2 alteration/MDM2 amplification and a peculiar nuclear atypia, advocating for their evaluation in biphasic tumours to facilitate accurate diagnosis and tailored posttumour removal monitoring. Further studies are warranted to validate these observations and elucidate their prognostic implications.

Characterization of a Molecularly Distinct Subset of Oncocytic Pleomorphic Adenomas/Myoepitheliomas Harboring Recurrent ZBTB47-AS1::PLAG1 Gene Fusion

Recurrent gene fusions are common in salivary gland tumors including benign tumors, such as pleomorphic adenoma (PA) and myoepithelioma (ME). In cases where chromosomal rearrangement is identified in the pleomorphic adenoma gene 1 (PLAG1) gene, different gene partners are found. Oncocytic metaplasia, characterized by oncocytes with abundant eosinophilic granular cytoplasm and hyperchromatic nuclei, is a well-known phenomenon in salivary gland neoplasms. However, the pure oncocytic variant of PA/ME showed PLAG1 gene rearrangements involving various gene partners at the molecular level, without any recurrent fusion being found. Our study includes 20 cases of PA/ME, with 11 females and 9 males. The age of patients ranged from 37 to 96 years, with a median age of 62.8 years. Most tumors originate from the parotid gland. The median size of the tumor was 26.5 mm (range: 13 to 60 mm). Among the 20 cases, 14 were a pure oncocytic variant of PA/ME, whereas 6 cases showed focal oncocytic or oncocytic-like aspects. Molecular studies on 20 cases of PA/ME were conducted. A novel recurrent ZBTB47-AS1::PLAG1 fusion was identified in 6 of 12 cases with pure oncocytic metaplasia, whereas the other cases had PLAG1 gene fusion with different gene partners. The transcriptomic analysis of the cases harboring ZBTB47-AS1::PLAG1 fusion demonstrated that these tumors have a distinct molecular profile from conventional PA/ME. This study reveals a unique subset in the oncocytic PA/ME spectrum characterized by pure oncocytic morphology with larger oncocytic cells and recurrent ZBTB47-AS1::PLAG1 fusion. It also highlights the transcriptomic distinctness of salivary gland adenomas with pure oncocytic metaplasia in the spectrum of salivary gland neoplasms. Further studies are needed to better understand the oncocytic variant of PA/ME and to determine the true nature of oncocytic cells in PA/ME.

Sialadenoma papilliferum-like intraductal papillary tumor with unveiling BRAF V600E and PIK3CA H1047R mutations: Case report with molecular analysis and literature review

INTRODUCTION

Sialadenoma papilliferum (SP), a rare minor salivary gland tumor, shares morphological and genetic similarities with syringocystadenoma papilliferum. Recent studies have identified BRAF V600E or HRAS mutations in SP, suggesting its neoplastic nature. Despite being uncommon, SP poses diagnostic challenges due to its resemblance to other lesions like squamous papilloma. The emergence of sialadenoma papilliferum-like intraductal papillary tumor (SP-IPT) further complicates its classification, emphasizing the need for thorough investigation.

CASE PRESENTATION

A 50-year-old male presented with a left palatal lesion histologically diagnosed as SP-IPT. Surgical resection revealed characteristic features, including papillary projections into cystically dilated ductal spaces. Immunohistochemistry confirmed positivity for pan-keratin AE1/AE3, cytokeratin 7, SOX10, and BRAF V600E. Whole-exome sequencing identified BRAF V600E and PIK3CA H1047R mutations. No recurrence was observed three months post-excision.

DISCUSSION

SP-IPT's diagnostic complexity stems from its resemblance to SP without an exophytic papillary component. However, shared BRAF mutations suggest a close relationship between the two entities. Similarities with skin adnexal tumors underscore the importance of molecular markers in tumor classification. The identification of PIK3CA mutation in SP-IPT adds to its molecular diversity, warranting further investigation into its clinical significance.

CONCLUSION

This study presents a case of SP-IPT with unique histological and molecular features, highlighting its diagnostic and therapeutic challenges. The co-occurrence of BRAF V600E and PIK3CA H1047R mutations suggests a distinct molecular profile in SP-IPT, necessitating further research to elucidate its biological behavior and clinical implications.

Primary thyroid rhabdomyosarcoma in an adult: A challenging case with histomolecular diagnosis and literature review

INTRODUCTION AND IMPORTANCE

Primary thyroid sarcomas are very rare tumours, accounting for less than 1 % of all thyroid malignancies. We present the fifth case in the literature of primary thyroid rhabdomyosarcoma and the third in adults with, for the first time, an extensive molecular analysis.

CASE PRESENTATION

A 61-year-old woman presented with a rapidly progressive neck mass with extensive local invasion of the tumour.

CLINICAL DISCUSSION

Histologically, the neoplasm was composed of sheets of pleomorphic or spindle-shaped cells with eosinophilic cytoplasm and few large and very pleomorphic cells admixed with the spindle cell proliferation, without any thyroid epithelial component. Immunohistochemically, the tumour cells were positive for muscular markers and negative for epithelial and thyroid differentiation markers. Molecular tests revealed the presence of NF1, PTEN and TERT pathogenic mutations. Classifying undifferentiated neoplasm with muscular differentiation into the thyroid is challenging as many more common differential diagnoses could be favoured including anaplastic thyroid carcinoma with rhabdoid phenotype, leiomyosarcoma, and other rare sarcomas.

CONCLUSION

Primary thyroid rhabdomyosarcoma is extremely rare and can be diagnostically challenging. We emphasize the histological, immunohistochemical and molecular criteria in order to make an accurate diagnosis.