Morphologic Diversity of Merkel Cell Carcinoma

Area of Science:

• Dermatopathology
• Oncology
• Histopathology

Background:

• Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine skin cancer with an unknown origin.
• Understanding MCC's diverse histological presentations is crucial for accurate diagnosis and treatment.

Purpose of the Study:

• To determine the frequency of unusual morphologic appearances in primary cutaneous Merkel cell carcinoma.
• To investigate associations between MCC and other cutaneous neoplasms or conditions.

Main Methods:

• Retrospective histologic review of 136 primary cutaneous MCC cases diagnosed between 1997 and 2018.
• Inclusion of a literature review to identify diverse MCC morphologies.

Main Results:

• Epidermotropism was observed in 8% of MCC cases.
• Associations with squamous cell carcinoma (10%), basal cell carcinoma (0.7%), and actinic keratosis (1.5%) were noted.
• Trabecular patterns (5%) and rosettes (2%) were identified; rare cases showed differentiation towards other cell lineages.

Conclusions:

• Merkel cell carcinoma exhibits varied histological appearances, including associations with other skin cancers and differentiation towards glandular, sarcomatous, or mesenchymal lineages.
• This morphological diversity underscores the complexity of MCC's pathogenesis.