MERKEL CELL CARCINOMA (TOKER 1972-ENDOCRINE CA OF THE SKIN)
I think of this entity like an aggressive amelonotic melanoma. If is caused by the Merkel cell polyomavirus (MCV) , discovered at the University of Pittsburgh in 2008, 80% of the time. It is also known as a cutaneous APUDoma, primary neuroendocrine carcinoma of the skin, primary small cell carcinoma of the skin, and trabecular carcinoma of the skin. It is a tumor of the tactile merkel cell in the stratum basale of the epidermis. Histologically it looks like small cell lung cancer with dense cohesive sheets of highly mitotic cells with scant cytoplasm. They are s-100 positive and are undifferentiated cells of neural crest origin.
It is a rare and aggressive neoplasm that behaves and even looks like an aggressive amelanotic melanoma. 55% present in the head and neck, 20% in the periorbital region, and primarily in the 6th decade of life. They are flesh colored and more than 50% overall have regional metastasis. Surgically we treat them like a melanoma. However, surgery alone is rarely the treatment plan as they seem to be radiosensitive. As up to 20% may have distant metastasis at presentation, PET scanning seems appropriate.
In the past we used to say 3 cm margins with lymphoscintigraphy alone for stage 1, 40 GY radiation for stage 2, and induction chemo for stage 3. Probably palliative chemo for stage 4.