Primary Sweat Gland Adenocarcinoma of the Skin With <i>ATL2::PRKD3</i> Fusion: A Potential Cutaneous Analog of Cribriform Adenocarcinoma of the Salivary Glands?

Many cutaneous adnexal tumors share molecular alterations with other homologous neoplasms occurring in salivary glands. Polymorphous adenocarcinoma (PAC) is a rare salivary gland tumor, usually associated with alterations in the PRKD gene family. In this report, we describe a primary cutaneous sweat gland adenocarcinoma of the scalp occurring in a 65-year-old female. Morphological features of the carcinoma were reminiscent of salivary gland PAC. Tumor cells were CK7+ S100+ SOX10+ p63 focally positive and p40-. Whole-transcriptome sequencing of the lesion showed the presence of an in-frame ATL2::PRKD3 fusion. PRKD1, 2 or 3 fusions are characteristic of the cribriform subtype of PAC (cribriform adenocarcinoma of salivary gland, CASG). No past history of salivary gland tumor nor existing salivary gland tumor was retrieved in the patient. After complete excision of the tumor, the patient has been in complete remission for 17 months. This case suggests that a subset of adnexal adenocarcinomas of not otherwise specified type (NOS) may carry PRKD alteration and may constitute the cutaneous counterpart of salivary gland PAC/CASG. This finding argues in favor of a more systematic molecular exploration of adnexal adenocarcinomas NOS for better classification and prognosis.