MERKEL CELL CARCINOMA

Case Provided by Jila Khorsand, MD

Case history

The patient is a 64 year old man with a firm, 2.5cm subcutaneous mass on his right leg. The lesion was excised with no complications.  Past history is remarkable for a T2.N0, moderately differentiated recto sigmoid adenocarcinoma, which was diagnosed in January of 2011.

Microscopic Findings

H&E slides showed a well circumscribed tumor composed of solid nests of small cells with high nucleo-cytoplasmic ratio and fine nuclear chromatin. Mitotic activity was brisk. Focal tumor necrosis was also noted.  Immunohistochemical stains showed the tumor cells to be ; CAM5.2 +, CK20+, CD56+, Chromogranin-A+, Synaptophysin+, and NSE+.  Tumor cells were; CD99 -, Vimentin -, WT-1-, CK7 -,  TTF1-, Smooth Muscle Actin -, CD45-, Melan-A -, and S100-.

Diagnosis

MERKEL CELL CARCINOMA

Discussion

Merckel cell carcinoma (MCC) is a rare and aggressive primary neuroendocrine carcinoma of skin.  Merkel cell carcinoma usually affects adults older than 50 and involves sun exposed areas of skin such as face, neck, head, arms and legs.  MCC is observed with increasing frequency in patients with immune deficiency such as patients with HIV infection, leukemia and organ transplant. MCC usually presents as a raised, red or violaceous papule or firm subcutaneous mass and a diagnosis is made by biopsy and microscopic examination of tissue, including a panel of immunoperoxidase stains.  In addition to routine neuroendocrine markers, CK20 positivity with characteristic perinuclear dot-like staining pattern is very useful in diagnosis of MCC and differentiating this entity from other mimicking tumors such as metastatic small cell carcinoma, melanoma, lymphoma and other small blue cell tumors. Staging of MCC is very important and directly related to survival of affected patients.

As of 2009 a new staging system has been established. Stage I is a primary tumor that is 2cm or smaller in size. Stage IIA is a primary tumor greater than 2cm and node negative by histopathologic examination, Stage IIB, is a primary tumor greater than 2 cm. and clinically or radio graphically node negative, Stage IIC, node negative primary tumor with extracutaneous invasion into muscle, bone or cartilage.  Stage IIIA is a tumor of any size with nodal micro metastasis. Stage IIIB, is a tumor of any size with macro metastasis and Stage IV, is a tumor of any size with distant metastasis.

 References

1.      AJCC Cancer Staging Manual, 7th. Edition, Springer, 2010

2      Shea, C. R. & V.G (2007) Dermatologic Manifestations of Merkel Cell Carcinoma. 

        Retrieved March 9, 2011, from http://emedicine.medscape.com/article/1100917-overview

3.     Merkel Cell Carcinoma. Seattle Cancer Care Alliance. http://www.merkelcell.org

H&E Stain; Medium Power Magnification: Soft tissue mass, solid and trabecular growth pattern
H&E Stain; High Power Magnification: High mitotic activity
H&E Stain; High Power Magnification: Soft tissue mass, focal necrosis
H&E Stain; High Power Magnification: Soft tissue mass, densely packed, small round cells with finely granular chromatin
IPOX Stain; High Power Magnification: Soft tissue mass, CAM 5.2
IPOX Stain; High Power Magnification: Soft tissue mass, CK20 with characteristic punctuate, perinuclear staining pattern
IPOX Stain; High Power Magnification: Soft tissue mass, CD56
IPOX Stain; High Power Magnification: Soft tissue mass, chromogranin-A
IPOX Stain; High Power Magnification: Soft tissue mass, synaptophysin