Low-grade sinonasal adenocarcinomas (low-grade SNACs) of the sinonasal
tract comprise a poorly characterized and histologically heterogeneous
group of tumors. We describe three cases of a histologically distinct
variant of low-grade SNAC characterized by ETV6 gene rearrangements. The
patients included 2 women (aged 32 and 88 y) and a man (aged 75 y); all
were initially treated with surgery alone. Follow-up ranged from 9 to
170 months with one patient having 2 local recurrences and none
experiencing distant or regional metastases. Tumors were composed of
cytologically bland columnar and cuboidal eosinophilic tumor cells with
basally located nuclei arranged in tubular and tubulotrabecular
patterns. Immunohistochemically, CK7, DOG1, GCDFP-15, and SOX10 were
positive in all cases, and vimentin was positive in 2 cases. Scattered
single cells or small groups of tumor cells were S-100 positive. Only
one case had weak, focal expression of GATA3, and mammaglobin was
consistently negative. Two cases had ETV6-NTRK3 gene fusions, whereas
ETV6 had an unknown fusion partner gene in one case. The highly similar
morphology, immunohistochemical profile, and genetics of the presented
cases are suggestive of a specific disease. Although
translocation-associated adenocarcinomas in the sinonasal tract have
previously been described exclusively as salivary-type carcinomas, we
present the first type of carcinoma characterized by recurrent genetic
rearrangements and distinct phenotype occurring exclusively in the
sinonasal tract with no known major salivary gland counterpart. We
provisionally designate this tumor ETV6-rearranged low-grade SNAC.
Identification of additional cases is necessary to fully appreciate the
morphologic and biological spectrum of this disease.