A Novel Fusion Gene CRTC3-MAML2 in Hidradenoma: Histopathological Significance

Publication date: Available online 24 October 2017
Source:Human Pathology
Author(s): Yuki Kuma, Yuichi Yamada, Hidetaka Yamamoto, Kenichi Kohashi, Takamichi Ito, Masutaka Furue, Yoshinao Oda
Hidradenoma usually presents a solitary, slow-growing, and solid or cystic nodular lesion, which arises in various anatomical sites. Its diagnosis is occasionally difficult because the tumor shares histological features with other cutaneous appendage tumors. Recently, CRTC1-MAML2 fusion gene was reported in hidradenomas, with the fusion transcript being demonstrated in approximately 50% of cases. However, limited information is available regarding its clinical significance. Here, we investigated the relationship between the fusion gene and clinicohistopathological features. We reviewed 39 cases histologically diagnosed as hidradenoma. RT-PCR was performed for all 39 cases, and fluorescence in situ hybridization (FISH) was also performed for the RT-PCR-negative cases. Results: The 39 tumors included 36 clear cell hidradenomas and 3 poroid hidradenomas. The details of the cellular components were as follows: clear-cell-dominant type, 9 cases; polygonal-cell-dominant type, 21 cases; and equally mixed type, 9 cases. There were no tumors with apparent mucinous cells. There were 8 tumors with prominent cystic change, 2 of which presented apocrine-like decapitated secretion. CRTC1-MAML2 fusion was detected in 10 of the 39 tumors (26%) and CRTC3-MAML2 fusion in 2 of the 39 (5%) by RT-PCR. MAML2 gene rearrangement was detected in 11 of 27 fusion-gene-negative cases by FISH. Moreover, neither the fusion genes nor gene rearrangement was detected in prominent cystic tumors and poroid hidradenomas. We conclude that CRTC1/3-MAML2 fusion gene analysis can be a useful method for diagnosing hidradenoma. Considering the histological and genetic similarity to mucoepidermoid carcinoma, hidradenoma may be a cutaneous counterpart of salivary gland mucoepidermoid carcinoma.



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