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