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Case Reports

Abstract

Primary cutaneous adenoid cystic carcinoma (PCACC) is a rare malignancy which shows similarities to adenoid cystic carcinoma of other organs including salivary gland and lung. MYB abnormalities are identified in approximately 60% of cases.

We present three cases of PCACC (2 males; 1 female; median age 81) occurring in three different locations: right axilla, scalp, and periumbilical region. All three cases were dermal/subcutaneous-based tumors showing varying amounts of cribriform, tubular, and solid architecture. The axillary and scalp tumors showed highly infiltrative growth patterns with perineural invasion; the axillary tumor involved the epidermis. In contrast, gross and microscopic examination of the periumbilical tumor revealed a well-circumscribed nodule in the dermis and subcutaneous tissue. None of the cases showed evidence of high-grade transformation. By immunohistochemistry, the tumor cells were positive for multiple keratins (3/3), p40 and/or p63 (2/3), and cKIT (2/3). MYB::NFIB fusion was detected in the scalp tumor by next-generation sequencing; the other two cases were not tested or negative for MYB rearrangements by fluorescence in situ hybridization.

One patient underwent sentinel lymph node biopsy which was negative for metastatic carcinoma. Importantly, in all three cases, the differential diagnosis included metastasis of adenoid cystic carcinoma of another site (especially salivary gland), requiring careful clinical correlation for definitive diagnosis. Other neoplasms in the differential diagnosis include spiradenoma/cylindroma and their malignant counterparts, adenoid-type basal cell carcinoma, and eccrine carcinoma not otherwise specified. Factors favoring PCACC include characteristic morphology and immunophenotype, perineural invasion, MYB translocation, and absence of an extracutaneous primary tumor on imaging.