Primary cutaneous NUT adnexal carcinoma: morphologic, genetic and methylation analysis of seven new cases with comparison to extracutaneous NUT carcinoma and NUTM1-rearranged porocarcinoma.

Abstract

NUT carcinoma is a rare malignant neoplasm characterised by recurrent NUTM1 rearrangements, initially reported in the midline. Recently, 10 cases of cutaneous NUT carcinoma with adnexal differentiation harbouring BRD3::NUTM1, NSD3::NUTM1, BRD4::NUTM1 or BRD3::NUTM2B fusions have been reported. Accordingly, 'NUT adnexal carcinoma' (NAC) has been introduced as a provisional tumour entity to the fifth edition of the WHO Classification of Skin Tumours.

Aims: We report the histopathological, molecular genetic and epigenetic features of seven additional cases of NAC.

Methods and results: The cohort consisted of four female and three male patients with a median age of 58 years. Follow-up was available for six cases, and documented diffuse metastatic spreading leading to death at 18 months after diagnosis for one case. Histopathological examination in all cases revealed dermal/subcutaneous neoplasms composed of poorly differentiated cells with large irregular vesicular nuclei and at least focally prominent nucleoli. All cases showed areas of duct/gland formation. Using immunohistochemistry, all tumours showed diffuse NUT expression with co-expression of SOX10 in five cases. P63 and P40 were diffusely positive in one case and confined to the periphery of the tumour nests in five cases. Molecular analysis showed BRD4::NUTM1 fusions (n = 3), BRD3::NUTM1 fusions (n = 3) and NSD3::NUTM1 (n = 1). Although being close to this latter group, methylation and transcriptional analysis revealed that NAC formed a unique cluster distinct from extracutaneous NUT carcinoma and NUTM1-rearranged porocarcinoma.

Conclusions: Our results further support the existence of primary cutaneous NAC and suggest that it may represent an entity distinct from extracutaneous NUT carcinoma.