BRAF p.V600E-negative low-grade adenocarcinoma of the mandible with features of sialadenopapillary ductal tumor and prominent mucinous differentiation: report of a unique case.

Cutaneous tubular adenoma (TA), also known as tubulopapillary hidradenoma, is a rare benign sweat gland tumor. In the oral cavity, 2 groups of glandular neoplasms morphologically similar to cutaneous TA have been previously described, under the names tubulopapillary hidradenoma-like tumor of the mandible (TPHLTM) and sialadenoma papilliferum-like intraductal papillary tumor (SP-IPT), respectively. Recent evidence suggests that sialadenoma papilliferum, SP-IPT, and TPHLTM may form a biological continuum, and a unifying term, sialadenopapillary ductal tumor (SDT), has been proposed for these lesions. However, the clinicopathological spectrum and biological behavior of SDTs remain poorly defined due to their rarity. Herein, we report a case of a 54-year-old woman with a mandibular tumor exhibiting morphological and immunohistochemical features akin to both cutaneous TA and SDT. Additionally, this tumor exhibited prominent mucinous differentiation and extensive mandibular bone destruction with infiltrative growth into adjacent soft tissues. Molecular analysis revealed no mutations in BRAF, HRAS, or PIK3CA genes. While the marked mucinous differentiation in our case may expand the pathological spectrum of SDT, the infiltrative growth pattern of this tumor further suggests a potential low-grade malignancy in a subset of SDT cases. The identification and analysis of additional cases should help to clarify the nosologic status and the biologic potential of this entity.