Track

Abstract

Microcystic adnexal carcinoma (MAC) is a rare, slow-growing, yet locally aggressive adnexal malignancy typically occurring on the central face. It is characterized by perineural invasion (seen in over 80% of cases) and infiltration beyond clinically apparent margins. Despite its limited metastatic potential, MAC has a high recurrence rate. We present a rare variant of MAC lacking overt adnexal differentiation on H&E, following immunostaining showed evidence of cutaneous adnexal origin and extension into the parotid gland via perineural spread. A 71-year-old male with a history of heart transplant and lymphoma presented with a 1.5 cm crusted erythematous plaque with 3–4 white papules superimposed on the plaque on the right buccal cheek. The biopsy and subsequent Mohs surgery was performed, for a superficially invasive carcinoma. During surgery, an infiltrative atypical solid and cystic proliferation was identified involving all margins. Permanent sections showed cysts of varying size and atypia with perineural invasion suggestive of MAC. Though adnexal differentiation is not significant, immunostaining of CK7, EMA, and CEA positivity supported MAC. Wide surgical re-excision revealed tumor with similar histologic features to the previous specimen, infiltrating through the skin into the parotid gland, with ductal differentiation, and extensive neurotropism. Immunohistochemistry was performed on the parotid gland, mirroring prior Mohs findings. Further confirming the diagnosis and the rarity of MAC extending into the parotid gland. The patient's immunocompromised status may be relevant, as MAC can occur in such contexts. This case underscores the diagnostic value of thorough histology, clinical correlation, and immunostaining in rare MAC