Unbalanced chromosomal rearrangements in a metastasizing salivary gland tumor with benign histology

Metastasizing Pleomorphic Adenoma: Recurrent PLAG1/HMGA2 Rearrangements and Identification of a Novel HMGA2-TMTC2 Fusion

Pleomorphic adenoma (PA) is the most common salivary gland neoplasm. On a molecular level PA is characterized by a translocation involving PLAG1 or HMGA2. PA is considered to be a benign tumor although it can undergo malignant transformation. Alternatively, cases of histologically benign PA "metastasizing" to lymph nodes or distant body sites are well documented. Several theories have been proposed to explain this behavior. However, there is a lack of molecular data available to assess the relationship of metastasizing PA (MPA) and their benign counterparts. In this study we describe 4 cases of MPAs and perform the first molecular study linking them to conventional PA. The index case was identified in the course of routine clinical practice, while the other cases were retrieved from the archives of the authors. Slides were reviewed to confirm the diagnosis of both the primary/recurrent tumor and the metastasis. Fluorescence in situ hybridization (FISH) was performed in all cases and RNA sequencing was performed on the index case. In all cases there was a history of recurrent PA involving the parotid. Lymph node metastases were identified in 2 cases; non-lymph node metastases were identified in 3 cases. All the metastases were histologically benign. RNA sequencing performed on the index case demonstrated a novel HMGA2-TMTC2 translocation, which was confirmed by separate FISH break-apart assays for both genes. FISH performed on the remaining cases demonstrated rearrangement of PLAG1 in all 3 cases. This study demonstrates that MPA harbors the same disease-defining molecular hallmark as their benign counterparts.

Metastasizing Pleomorphic Adenoma Case Report and Review of the Literature

Pleomorphic adenoma (PA) is by far the most common salivary gland tumor. It is well known that PA can undergo malignant transformation. However, in rare occasions it can metastasize preserving its benign phenotype. Metastasizing pleomorphic adenoma (MPA) constitutes an extremely rare tumor. Here we are reporting an unusual MPA affecting the mandible that was preceded by a submandibular gland pleomorphic adenoma.

Genomic copy number alterations of primary and secondary metastasizing pleomorphic adenomas

AIMS

Metastasizing pleomorphic adenoma (MPA) is a rare tumour, and its mechanism of metastasis still is unknown. To date, there has been no study on MPA genomics. We analysed primary and secondary MPAs with array comparative genomic hybridization to identify somatic copy number alterations and affected genes.

METHODS AND RESULTS

Tumour DNA samples from primary (parotid salivary gland) and secondary (scalp skin) MPAs were subjected to array comparative genomic hybridization investigation, and the data were analysed with NEXUS COPY NUMBER DISCOVERY. The primary MPA showed copy number losses affecting 3p22.2p14.3 and 19p13.3p123, and a complex pattern of four different deletions at chromosome 6. The 3p deletion encompassed several genes: CTNNB1, SETD2, BAP1, and PBRM1, among others. The secondary MPA showed a genomic profile similar to that of the primary MPA, with acquisition of additional copy number changes affecting 9p24.3p13.1 (loss), 19q11q13.43 (gain), and 22q11.1q13.33 (gain).

CONCLUSION

Our findings indicated a clonal origin of the secondary MPA, as both tumours shared a common profile of genomic copy number alterations. Furthermore, we were able to detect in the primary tumour a specific pattern of copy number alterations that could explain the metastasizing characteristic, whereas the secondary MPA showed a more unbalanced genome.

Parotid pleomorphic adenoma with solitary renal metastasis

We present a rare case of renal metastasis of a recurrent pleomorphic adenoma of the parotid gland in an elderly woman. Metastasising pleomorphic adenoma shows malignant clinical behaviour, and although it appears histologically benign, there may be unknown molecular features that determine its unusual ability to spread.

Heterogeneous genetic profiles in soft tissue myoepitheliomas

Myoepithelioma, mixed tumor and parachordoma are uncommon soft tissue tumors thought to represent morphological variants of a single tumor type. The genetic basis of these neoplasms is poorly understood. However, they morphologically resemble mixed tumor of the salivary glands (also known as pleomorphic adenoma), a tumor characterized by deregulated expression of PLAG1 or HMGA2. To evaluate a possible genetic relationship between these soft tissue and salivary gland tumors, PLAG1 expression levels and the genomic status of PLAG1 and HMGA2 were investigated in five soft tissue myoepitheliomas and one pleomorphic adenoma. In addition, all tumors were cytogenetically investigated and whole genome DNA copy number imbalances were studied in five of them. The genetic profiles were heterogeneous and the only aberration common to all soft tissue myoepitheliomas was a minimally deleted region of 3.55 Mb in chromosome band 19p13. Recurrent deletion of CDKN2A suggests that inactivation of this tumor suppressor gene is pathogenetically important in a subset. Furthermore, PLAG1 rearrangement was found in a soft tissue tumor from a patient previously treated for a salivary pleomorphic adenoma, indicating either metastasis of the salivary gland lesion or that some soft tissue tumors develop through the same mechanisms as their salivary gland counterparts.

Metastasizing Pleomorphic Adenoma of the Salivary Gland

Metastasizing pleomorphic adenoma of salivary glands is a group of rare tumors that are histologically identical to benign mixed tumors and that inexplicably metastasize. A review of the literature revealed that it usually occurs after multiple local recurrences, and the interval between diagnosis of primary pleomorphic adenoma and metastases ranges between 3 and 52 years. The most common site for metastasis is bone, followed by the head and neck and lung. No histologic or molecular parameters exist at the present time that could predict the development of metastasis in these neoplasms. Metastasectomy confers significant survival advantage over nonoperative treatment for localized and accessible metastases, but there is no definite treatment protocol available in cases of widespread metastases.

Multiple Pulmonary Metastases from Benign Pleomorphic Adenoma

Metastasizing pleomorphic adenoma is a rare condition of metastasis from a histologically benign salivary gland tumor. We report a case of metastasizing pleomorphic adenoma presenting with multiple bilateral lung metastases, and discuss the clinical aspects of this disease.

'Metastasizing pleomorphic salivary adenoma' should now be considered a low-grade malignancy with a lethal potential

PURPOSE OF REVIEW

To review the current knowledge on the clinical entity of metastasizing pleomorphic adenoma.

RECENT FINDINGS

Using case studies, the literature continues to explore the potential to identify a chromosomal abnormality that might explain the clinical entity, and may constitute a submicroscopic malignant transformation with molecular genetic alterations. Presently there are no agreed histopathological parameters that can identify or confirm a difference in behavior between the 'common' pleomorphic adenoma from the metastasizing pleomorphic adenoma.

SUMMARY

The evidence supports that metastasizing pleomorphic adenoma is most likely to be an unrecognized and as yet unclassified malignant neoplasm and as such must be considered a low-grade, potentially lethal malignant disease when it presents, which may constitute a submicroscopic malignant transformation with molecular genetic alterations. Further research is required to answer the many questions.

Benign metastasizing pleomorphic adenoma of the parotid gland: A clinicopathologic puzzle

BACKGROUND

Pleomorphic adenoma constitutes the most common benign parotid gland tumor. Local recurrence after surgical treatment (lateral or total parotidectomy) has been described in 1% to 5% of cases. Malignant degeneration has been reported in 2% to 9% of cases of pleomorphic adenoma of salivary gland origin. Metastasizing pleomorphic adenomas without histologic evidence of malignancy have rarely been reported. Metastatic lesions have been discovered in bone, lymph nodes, the lung, oral cavity, pharynx, skin, liver, retroperitoneum, kidney, calvarium, and central nervous system. To the best of our knowledge, we hereby report the first case of pleomorphic adenoma of the parotid gland metastasizing to the ipsilateral maxilla.

METHODS

We simultaneously examined apoptosis-related protein expression and markers of cell-proliferation activity in our case of benign pleomorphic adenoma metastasis and compared outcome with a control group of primary parotid pleomorphic adenomas.

RESULTS

Analysis of p53, Bcl-2, MIB1, CD 105, p27, and p21 expression did not reveal significant differences between metastasizing pleomorphic adenoma of the salivary gland and the control group of primary parotid pleomorphic adenomas.

CONCLUSIONS

Clinical rather than pathologic evidence seems to justify inclusion of metastasizing salivary pleomorphic adenoma in the group of low-grade malignant salivary tumors.