Dermatology Xagena

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Hidradenoma, a novel fusion gene CRTC3-MAML2

Hidradenoma usually presents as 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.

Researchers have investigated the relationship between the fusion gene and clinicohistopathological features.
39 cases histologically diagnosed as hidradenoma were reviewed.

Reverse-transcription polymerase chain reaction ( RT-PCR ) was performed for all 39 cases, and fluorescence in situ hybridization was also performed for the RT-PCR-negative cases.

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 fluorescence in situ hybridization.

Moreover, neither the fusion genes nor gene rearrangement was detected in prominent cystic tumors and poroid hidradenomas.

In conclusion, 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. ( Xagena )

Kuma Y et al, Hum Pathol 2017;70 : 55-61