Primary Neuroendocrine (Merkel Cell) Carcinoma



Primary Neuroendocrine (Merkel Cell) Carcinoma


David Cassarino, MD, PhD





Key Facts


Terminology



  • Cutaneous neuroendocrine carcinoma


Clinical Issues



  • Highly aggressive tumors with greater metastatic potential than melanoma


  • Rare (approximately 470 cases/year in USA)


  • Typically occur in sun-damaged skin of elderly


  • More common in males


  • Radiotherapy is generally used


Microscopic Pathology



  • Highly atypical basaloid neoplasm composed of infiltrative cords, trabeculae, and sheet-like areas


  • Typically dermal-based, but may show epidermal (pagetoid) involvement in up to 20% of cases


  • Numerous mitoses and apoptotic bodies


  • Nuclear crush artifact and streaming may be seen, similar to small cell carcinomas


  • Basaloid cells with high N:C ratio, scant cytoplasm, large nuclei, granular to clear chromatin, and indistinct nucleoli


Ancillary Tests



  • Immunohistochemistry is important in confirming diagnosis and excluding metastatic carcinoma


  • MCC is typically positive for keratins, including CK20, with perinuclear dot-like staining


Top Differential Diagnoses



  • Basal cell carcinoma (BCC)


  • Metastatic small cell carcinoma (especially pulmonary origin)


  • Small cell melanoma







Low magnification of Merkel cell carcinoma shows diffuse dermal involvement by sheets and nodules of atypical basophilic cells. There is a thin grenz zone separating the tumor from the epidermis image.






High magnification of MCC shows nuclear molding, hyperchromasia, and vesicular to granular-appearing chromatin. Numerous apoptotic and mitotic figures image are easily identified.


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



    • Merkel cell polyoma virus infection is found in up to 90% of cases


  • Associated with immunosuppression



    • 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



    • Rare



      • Approximately 470 cases/year in USA


  • Age



    • Typically in elderly patients (> 65 years old)


  • Gender



    • Male > female (2.5:1)


  • Ethnicity



    • 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



    • 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



    • Complete and wide excision to ensure complete local removal


    • 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



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


    • Chemotherapy is less effective and does not prolong overall survival


Prognosis

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Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Primary Neuroendocrine (Merkel Cell) Carcinoma

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