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Merkel cell skin cancer (neuroendocrine skin cancer): a rare type of skin cancer.

What is Merkel Cell Skin Cancer?
Merkel cell skin cancer (MHDC) is a rare, fast-growing, aggressive neuroendocrine tumor of the skin. It was defined as “trabecular carcinoma of the skin” in 1972. Today, it is accepted that the tumor originates from the “Merkel Cells” located in the basal layer of the epidermis and acting as a touch receptor.
It is usually seen in individuals over the age of 65, but it can be encountered in a wide age spectrum from childhood to advanced ages. There is no difference in frequency between men and women. MHDC is frequently seen on sun-exposed body areas [face and extremities (arms and legs)]. In more than 50% of cases, the tumor is located in the head and neck region, although the lesion can also be seen in other parts of the body. MHDC is a painless and rapidly growing skin lesion that does not present a typical clinical picture. Clinically, it is a raised, dome-like nodule, indurating plaque, and sometimes pedunculated, red-violet or dark purple-colored skin lesions with various appearances. It is single. In most patients, the tumor diameter is usually less than 2 cm at first admission.
The diagnosis is made by removing the entire lesion on the skin (total excision; excisional biopsy) and sending it to pathology. The tumor can be confused with lymphoma, primary and metastatic small cell carcinoma, malignant melanoma and other skin cancers, therefore, immunohistochemical examination is often required. If enlargement of the lymph nodes is detected during the examination of the patient, a tissue sample is taken from the lymph node with fine needle or tru-cut biopsy and pathological examination is performed. If the diagnosis is MCC in the pathology report, distant metastasis screening (FDG-PET SCAN, DOTA-PET SCAN) and then treatment are planned.
How is the staging in Merkel Cell Skin Cancer?
Stage I (T1N0M0)Tumor diameter < 2 cm No lymph nodes and distant metastases
Stage II (T2N0M0)Tumor diameter ≥ 2 cm No lymph nodes and distant metastases
Stage III (T1/T2N1M0)Regardless of tumor diameter, there is lymph node metastasis, no distant metastasis.
Stage IV (T1/T2N0/N1M0)There is distant metastasis regardless of tumor size and lymph node metastasis.
What is the Treatment of Merkel Cell Skin Cancer?
Although the treatment varies according to the stage of the disease, the main treatment is surgery. Except for selected stage IV patients, the treatment of the disease is surgery. Surgical treatment is applied for the skin and lymph nodes.
Surgical treatment:
*Extensive removal of the primary lesion area and sentinel lymph node biopsy (guard lymph node biopsy, lymphatic mapping) is performed in early stage (Stage I and II disease without lymph node and distant metastasis) patients. Patients with no metastasis in the sentinel lymph node are followed up, and the 5-year survival is around 97% in these patients. In patients with microscopic metastasis in the sentinel lymph nodes, lymph node dissection is performed for the lymph nodes in the relevant lymph node.
*In patients with lymph node metastasis (Stage III disease), surgery is performed on the skin and lymph region in the same session. The primary lesion area on the skin is widely removed, and repair is performed if necessary by placing a patch. For the treatment of enlarged lymph nodes, the lymph nodes in the lymph region are surgically removed (lymph node dissection).
Patients in whom radiotherapy can contribute to the provision of local control should be identified and treatment should be applied. In selected patients, radiation therapy is applied to the lymph region, and in patients with distant metastases, to the metastasis region.
There is no standard scheme for systemic therapy. Although the role of chemotherapy in the treatment has not been clarified yet, combinations of chemotherapy that are effective in small cell lung cancers are applied. Adjuvant therapy is generally not recommended in stage I and II disease. In these patients, 5-year survival is over 90%. Adjuvant treatment conditions should be reviewed in stage III disease. Systemic chemotherapy is indicated in stage IV disease.
The patient diagnosed with Merkel Cell Skin Cancer is both at the stage of diagnosis and treatment. skin oncology group should be evaluated and treatment/follow-up planning should be made. In early stage patients, head and neck location, tumor diameter (>2 cm), mitosis rate (>10 BB), presence of vascular and lymphatic invasion are important. The patient should be taught self-examination and a follow-up program should be arranged.

Prof.Dr.Sıdıka Board Plastic, Reconstructive and Aesthetic Surgery Specialist
IU. Oncology Institute, Capa, Istanbul