Merkel Cell Carcinoma

Merkel Cell Carcinoma
Clinical
:diamonds: An aggressive neoplasm typically presenting as a
slowly growing nodule on the sun exposed skin (head
and neck region) of older adults
:diamonds: The recurrence and metastatic rate is approximately
40-50%
Microscopic
:diamonds: A variety of histologic forms may be seen and include
sheet-like, ribboned, nested, trabecular and organoid
variants
:diamonds: Pseudorosettes may be prominent
:diamonds: These tumors are typically dermal based but frequently
involve the subcutis and may show an intraepidermal
growth pattern
:diamonds: Focal areas of squamous, eccrine or sebaceous differ-
entiation may be seen, and these tumors may arise in
conjunction with another, histologically distinct
neoplasm
:diamonds: The cytologic and immunophenotypic appearance is
characteristic and common to all variants
:diamonds: Cytologically, the tumor cells have very high nuclear/
cytoplasmic ratios, indistinct cell borders, hyperchro-
matic, and finely granular nuclei with inconspicuous
nucleoli and thin nuclear membranes
:diamonds: Nuclear molding and mitoses are abundant
:diamonds: Immunophenotypically, the tumor cells express low
molecular weight cytokeratin (CAM 5.2) in a peri-
nuclear dot-like pattern which may also be seen with
neurofilament staining
:diamonds: Cytokeratin 20 staining is generally positive, and these
tumors express a variety of neuroendocrine markers
including neuron-specific enolase, chromogranin,
synaptophysin and neurofilament, but are generally
negative for S100 and vimentin