Introduction:
The surface layer of the skin is called the epidermis. Merkel cells are found inside the epidermis, a type of neuroendocrine cell (both nervous and endocrine systems). They are seen near the nerve endings providing a tactile sensation. They also have a substance that plays the role of hormones. Cancer that originates in the Merkel cells is called Merkel cell carcinoma.
What Is Merkel Cell Carcinoma?
Merkel cell carcinoma is an aggressive cancer of the skin. It can be life-threatening and is usually rare. Merkel cell carcinoma originates in the epidermis, the outer layer of the skin. It usually metastasizes quickly to adjacent lymph nodes and other organs like the lungs, brain, bones, etc. Merkel cell carcinoma has a higher chance of recurrence even after the surgical removal of the tumor. They are also called neuroendocrine cancer of the skin or trabecular cancer.
What Causes Merkel Cell Carcinoma?
The common causes of Merkel cell carcinoma are -
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Ultraviolet Radiation - Ultraviolet radiation from the sun, sunburns, or indoor tanning can cause Merkel cell carcinoma.
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Weak Immune System - People with a weak immune system cannot suppress the virus-causing tumor. Thus the virus produces a protein that will help in tumor growth.
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Viral Infections - Viral infections like HIV (human immunodeficiency virus) and AIDS (acquired immunodeficiency syndrome) can result in Merkel cell carcinoma.
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Immunosuppressants - People who take immunosuppressants like those in organ transplant medications can also result in Merkel cell carcinoma.
What Are the Symptoms of Merkel Cell Carcinoma?
They are seen in sun-exposed areas like the face, neck, arms, etc. The most common sign of Merkel cell carcinoma is the presence of a lump. The lump seen in Merkel cell carcinoma is usually firm and itchy, grows quickly, is raised, red in color, and will have tenderness.
How Is Merkel Cell Carcinoma Diagnosed?
Merkel cell carcinoma is diagnosed by a series of tests -
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Physical Examination - A general physical examination of the body to check for any signs of disease like lumps, pain, etc.
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Past Medical and Family History - Past health history, treatment received, personnel habits, or familial history of cancer are considered.
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Skin Biopsy - A small portion of skin cells or tissue is removed and viewed under a microscope to check for any abnormal growth of cells.
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Computed Tomography (CT) Scan - Using high radiation and computer technology, a cross-sectional image of the internal organs is produced to check for abnormal growth, cancer involvement, or metastasized cancer.
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Positron Emission Tomography (PET) Scan - A radioactive drug is inserted into the body to check for any abnormal metabolic activities taking place inside the body.
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Sentinel Lymph Node Biopsy (SLNB) - The first lymph node involved in the primary tumor's lymphatic drainage is the sentinel lymph node. Sentinel lymph node biopsy is performed to know the lymph node involvement in any cancer. Positive sentinel lymph node biopsy result confirms that the tumor has spread to adjacent lymph nodes.
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Lymph Node Dissection - Lymph nodes are removed by a surgical procedure and examined under a microscope to confirm cancer involvement. There are two types of lymph node dissection- regional and radical. In regional lymph node dissection, some of the lymph node present in a tumor site is removed. In radical lymph node dissection, all the lymph nodes present in the tumor area are removed.
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Core Needle Biopsy - With a wide needle's help, a tissue sample is removed and observed under the microscope.
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Fine Needle Aspiration Biopsy - With the help of a thin needle, a tissue sample is removed and observed under the microscope to confirm cancer involvement.
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Immunohistochemistry - With the help of certain antibodies, tumor markers or antigens can be identified. This help to differentiate different types of cancers.
What Are the Treatment Options for Merkel Cell Carcinoma?
The treatment of Merkel cell carcinoma is based on the stage of cancer. Merkel cell carcinoma is staged from stage 0 to stage 4, depending on the extent of the tumor's spread. Early-stage Merkel cell carcinoma is more easily treatable than the advanced stages. Recurrent or metastatic Merkel cell carcinoma is difficult to cure, so palliative care is advised. Adjuvant therapy is used after surgical therapy to prevent the recurrence of Merkel cell carcinoma.
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Surgical Therapy - Surgical therapy can be performed by three methods based on the spread of the tumor. Mohs surgery is usually used to treat cancer involving the skin. In this surgery, thin layers of the skin are cut and checked for signs of cancer. When the skin layer shows no signs of cancer, then the process of cutting is stopped. In Mohs surgery, all the cancer cells are removed without involving the healthy skin cells around the cancer. By removing all the cancer cell layer, Mohs surgery will prevent the recurrence of cancer and helps in the complete cure of cancer. Another surgical method of removing Merkel cell cancer is wide local excision, in which cancer cells and surrounding healthy cells are removed. Then, lymph node dissection is done to remove the lymph nodes with cancer involvement.
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Chemotherapy - Using high dosages of drugs to kill the cancer cells or prevent the growth of the cancer cells. It can be administered by two methods, oral (through the mouth) and systemic (intravenously) administration. Cisplatin, Carboplatin, Etoposide, and Topetecan are the commonly used chemotherapeutic drugs. Chemotherapy is used as an adjuvant treatment after the surgical removal of cancer to prevent cancer recurrence.
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Radiation Therapy - Using high radiation to kill cancer cells and prevent cancer growth. In Merkel cell carcinoma, external beam radiation therapy is used, which is done with the help of a machine. In advanced Merkel cell carcinoma, which is recurrent and metastatic, to give palliative therapy and, to relieve the symptoms, radiation therapy is given.
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Immunotherapy - Immunotherapy uses our immune system to fight against cancer cells.
Conclusion:
Merkel cell carcinoma is a very rare skin cancer. It is aggressive cancer and is highly metastatic. It usually spreads through the lymphatic system. Merkel cell carcinoma will usually reoccur after the treatment. So continuous follow-up is needed every three to four months duration. Avoid getting direct sunlight or sunburns, and use sunscreen with an SPF (sun protection factor) of 60 while sunlight is exposed daily.
