Background Hidradenoma papilliferum (HP) is a rare, benign epithelial tumour arising from the anogenital mammary-like glands, that occurs almost exclusively in the anogenital region of middle-aged women. To-date, genetic characterisation of HP has identified recurrent somatic mutations in PIK3CA and AKT1, which appear to be mutually exclusive, and PIK3R1 mutations in some cases without PIK3CA or AKT1 mutations. However, these studies used small sample sizes and/or analysed a limited number of genes, thus the mutational landscape of HP remains incomplete.

Objectives To better understand the molecular pathogenesis of HP by exploring the mutational landscape of these rare tumours and identifying candidate driver events.

Methods In this retrospective, multi-institutional study, we collated a cohort of formalin-fixed paraffin-embedded HP cases (n=68) to perform whole-exome sequencing and RNA-sequencing.

Results PIK3CA and PIK3R1 were identified as significantly mutated, and thus, are statistically predicted driver genes of HP. The mutations, which were predominantly at known hotspots, were all predicted to be oncogenic/likely oncogenic. Mutation of PIK3CA and PIK3R1 were mutually exclusive, consistent with these genes each encoding a subunit of the heterodimeric enzyme, PI3 kinase (PI3K), which functions via the PI3K/AKT/mTOR signalling pathway. Somatic mutations were also identified in other members of the PI3K/AKT/mTOR pathway (AKT1/2), receptors or receptor-associated proteins that signal via the PI3K/ATK/mTOR pathway (ERBB3, IRS2), or members of pathways that crosstalk with the PI3K/AKT/mTOR pathway (AR and MAPK1). The copy number landscape of HP revealed no recurrent alterations. Fusion gene analysis identified fusions in individual samples (SMARCD3::ASXL2, STX17::ERO1B, ANKFY1::UBE2G1, IQGAP1::ZNF774 and EXOC2::FRMD4B), with only the latter two being previously reported in other cancer types. No significant evidence of human papillomavirus (HPV) sequence was found in the tumour samples.

Conclusions Comprehensive characterisation of the mutational landscape of HP identified PIK3CA and PIK3R1 as mutually exclusive driver genes. Taken together with mutation of other genes involved in PI3K/AKT signalling, our findings confirm a key role of the alteration of this pathway in the pathogenesis of HP. The absence of HPV sequences suggests HPV is not involved in the aetiology of HP.

The authors have declared no competing interest.

This study was supported by a Medical Research Council (MRC) program grant to D.J.A. (MR/V000292/1) and the Wellcome Trust (220540/Z/20/A).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

This study is part of the DERMATLAS Project that has been approved by the NHS Health Research Authority; Research Ethics Committee (REC) reference: 21/PR/1024, IRAS project ID: 304621.

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The sequencing data is available in the European Genome and Phenome Archive (EGA) repository (https://www.ebi.ac.uk/ena/browser/home) under the study accessions EGAD00001015481 for whole exome data, and EGAD00001015480 for RNA-seq data.