Microcystic adnexal carcinoma: a distinct clinicopathologic entity

Area of Science:

• Dermatopathology
• Oncology

Background:

• Microcystic adnexal carcinoma (MAC) is a rare neoplasm.
• It is often misdiagnosed as benign adnexal neoplasms due to similar histological features.
• Recognition is crucial for appropriate management.

Purpose of the Study:

• To describe the clinical and histological features of six cases of MAC.
• To highlight the diagnostic challenges posed by MAC, especially on initial biopsy.
• To elucidate the potential cell of origin for MAC.

Main Methods:

• Retrospective analysis of six histologically confirmed cases of MAC.
• Review of clinical presentation, including patient demographics and lesion characteristics.
• Detailed examination of histopathological findings, focusing on stromal and cellular morphology.
• Assessment of deep tissue invasion and perineural involvement.

Main Results:

• All six cases presented with benign histological features on initial biopsy.
• Lesions typically appeared as solitary, flesh-colored, indurated plaques on the upper lip.
• Histology showed islands of basaloid keratinocytes in a desmoplastic stroma, with ductal and gland-like structures.
• Deep invasive components demonstrated infiltration of collagen, skeletal muscle, and perineural spaces, despite rare cytologic atypia and mitotic figures.

Conclusions:

• MAC can exhibit benign histological features, leading to diagnostic confusion.
• The neoplasm appears to arise from pluripotential adnexal keratinocytes with dual follicular and sweat gland differentiation.
• Accurate diagnosis requires careful evaluation, especially of deep tissue components.