Secretory Carcinoma of the Skin: Report of 6 Cases, Including a Case With a Novel NFIX-PKN1 Translocation.

Secretory carcinoma of the skin is a rare adnexal carcinoma, which is morphologically and immunohistochemically identical to secretory carcinoma of the breast and is associated with the presence of t (12;15) translocation, resulting in the ETV6-NTRK3 gene fusion. Nineteen cases of primary cutaneous secretory carcinoma have been previously published in the literature. In this study, we describe 6 new cases of secretory carcinoma of the skin. The study group consisted of 5 female patients and 1 male patient, ranging in age from 57 to 98 years (mean: 74.2, median: 74). Locations included the axilla (2), neck, eyelid, thigh, and nipple base, each one. Microscopically, all but 1 tumor were well circumscribed and nonencapsulated and exhibited characteristic abundant secretions within the microcystic and tubular spaces comprised by bland oval, round to cuboidal neoplastic cells. In addition, solid areas and focal pseudopapillae were seen, and, in 1 case, a focal mucinous component with small lakes of mucin containing small tumor nests or tubules of the neoplastic cells was present. The remaining neoplasm was mostly solid and papillary, with only few characteristic lumina containing secretions. Immunohistochemically, all cases expressed S-100 protein, mammaglobin, STAT5, GATA3, and NTRK. ETV6-NTRK3 gene fusion was detected in 5 cases, whereas, in the remaining tumor, a novel NFIX-PKN1 gene fusion was found.