Morphologically high-grade microcystic adnexal carcinoma: a report of two cases

Microcystic adnexal carcinoma is a distinctive sweat duct carcinoma of low-grade malignant potential with a risk for locally destructive growth and local recurrence. Distant metastases and disease-related mortality are exceptional. The histological hallmarks of these tumours are the diffusely infiltrative growth within the dermis, the frequent invasion of subcutaneous structures, the presence of perineurial invasion, and the bland cytological features. The tumours are organised in cords and strands, and show keratocyst formation and duct differentiation in varying proportions. Marked cytological atypia, nuclear pleomorphism, brisk and atypical mitotic activity and necrosis are not typically seen in these tumours.

We report two patients presenting with large, slowly growing tumours on the face showing areas of morphologically high-grade carcinoma arising on a background of unequivocal microcystic adnexal carcinoma. Both patients are alive with follow-up of up to 6 years, with no evidence of disease.

Morphologically high-grade transformation in microcytic adnexal carcinoma is a rare phenomenon that does not appear to confer a risk for aggressive behaviour. Recognition depends on sampling of the areas of conventional microcystic adnexal carcinoma.