Merkel cell carcinoma
Merkel cell carcinoma is an uncommon neuroendocrine tumor of the dermis which is characterized by aggressive regional nodal invasion, distant metastases, and a high rate of recurrence. Merkel cell carcinoma arises from Merkel cells, which are mechanoreceptor cells present in the skin.
Epidemiology
Merkel cell carcinoma typically occurs in elderly fair skinned individuals in the seventh and eighth decades of life, with a slight male predilection. Ultraviolet radiation, Merkel cell polyomavirus, and immunosuppression have been reported as risk factors.
Clinical presentation
It often presents as a non-specific erythematous or violaceous firm nodule or small plaque that may be surrounded by small satellite tumors, typically in sun exposed areas . It may be difficult to differentiate clinically form a basal cell carcinoma.
Pathology
Merkel cell carcinoma typically arises form the dermis with invasion of the subcutis, usually without involvement of the epidermis . Merkel cell polyomavirus is thought to play a greater role in pathogenesis in high latitudes, being present in 80% of Merkel cell carcinomas . Loco-regional metastases is present in 30% of patients at diagnosis .
Radiographic Features
Due to its rarity, imaging findings have only been reported in case reports and a few case series.
Ultrasound
- hypoechoic solid nodules arising from the dermis, with variable degrees of invasion and posterior acoustic transmission
CT
- area of high attenuation within soft tissue
- associated lymphadenopathy
- readily enhances with contrast
PET
- FDG avid hyper-metabolic lesion
Treatment and prognosis
Excision of the tumor, usually with adjuvant radiotherapy is the first line of therapy for localized disease. New immune checkpoint inhibitors have recently been demonstrated to be efficacious in advanced or refractory disease .
Merkel cell carcinoma has a poor prognosis. Although it accounts for an estimated 1% of all cutaneous skin cancers, it is the second leading cause of death from skin cancer behind melanoma.
History and etymology
It was first reported by Cyril Toker (1930-2015) in 1972 .
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