Primary Neuroendocrine (Merkel Cell) Carcinoma

 Especially lung, which are TTF-1(+), CK20(-)



• Small cell melanoma

• Lymphoma



image
Clinical Photograph of MCC
Clinical photograph of Merkel cell carcinoma (MCC) shows a well-circumscribed, erythematous dermal nodule. (Courtesy J. Wu, MD.)


image
MCC Involving Superficial Dermis
The superficial dermal portion of this tumor shows enlarged, crowded and markedly atypical-appearing basaloid cells with several large, atypical mitotic figures image easily identified.

image
Higher Magnification of MCC With Lymphatic Invasion
High magnification of the superficial dermal portion of this tumor shows enlarged, atypical basaloid cells with several frankly atypical mitotic figures image. Invasion of a superficial lymphatic vessel is also seen image.

image
High Magnification of MCC
Nuclear clearing image is often seen in MCC, a feature not seen in basal cell carcinoma or most other small round blue cell tumors. Note the numerous apoptotic bodies image and mitotic figures image.


TERMINOLOGY


Abbreviations




• Merkel cell carcinoma (MCC)


Synonyms




• Cutaneous neuroendocrine carcinoma

• Primary small cell carcinoma of skin

• Trabecular carcinoma


Definitions




• Malignant proliferation of cutaneous neuroendocrine cells


ETIOLOGY/PATHOGENESIS


Infectious Agents




• Recent studies have shown strong link to infection with polyomavirus
image Merkel cell polyoma virus infection is found in > 90% of cases by PCR studies

• Associated with immunosuppression
image Organ transplant and HIV(+) patients have much higher incidence


Cell of Origin




• Postulated to represent malignant transformation of cutaneous neuroendocrine (Merkel) cells or pluripotent stem cells, but this remains speculative


CLINICAL ISSUES


Epidemiology




• Incidence
image Rare

– < 500 cases/yr in USA

• Age
image Typically in elderly patients (> 65 yr old)

• Sex
image M > F (2.5:1)

• Ethnicity
image Caucasians much more commonly affected than other races


Site




• Sun-damaged skin

• Usually head and neck or extremities


Presentation




• Dermal nodular or plaque-like mass lesion
• Rapidly enlarging dermal mass lesion

image May be ulcerated &/or hemorrhagic


Natural History




• Aggressive tumors with high incidence of local recurrence, lymph node, and distant metastasis

• Clinical staging should include imaging studies, especially chest and abdominal CT scans


Treatment




• Surgical approaches
image Complete and wide excision to ensure complete local removal

image Consideration may be given to sentinel lymph node (SLN) biopsy

– However, SLN positivity does not seem to be very sensitive for regional lymph node involvement, as many patients progress to distant metastases

• Adjuvant therapy
image Radiotherapy is generally used and may lead to remission in some cases

image Chemotherapy is less effective and does not prolong overall survival


Prognosis




• High incidence of recurrence (up to 30%) and metastasis (up to 75%)
• Overall prognosis is poor

image Death due to disease is high, even with treatment

image Worse prognosis associated with advanced age, head and neck location, large size, and immunosuppression

Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Primary Neuroendocrine (Merkel Cell) Carcinoma
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