Merkel Cell Carcinoma


Definition

Merkel cells are situated in the top most layer of the skin which is very near to the nerve endings that accept the touch sensation. Merkel cell carcinoma (MCC) which is also known as neuroendocrine carcinoma or trabecular cancer is a rare cancer that occurs when the growth of Merkel cells in the skin is out of control.

merkel cells


Image 1 – Merkel Cells of skin

MCC usually begins in areas of the skin that is exposed to sunlight such as the head, trunk, neck, legs, and arms. The growth can enlarge rapidly and appears as firm, and flesh-colored bump. MCC is also an aggressive type of cancer which means that it could metastasize or spread quickly even at an early stage. The condition is common in individuals who are over 65 years old, had received an organ transplant, with fair skin, and had a history of extensive exposure to the sun.


merkel cell carcinoma over foot

Image 2 – Merkel Cell Cancer over foot

Merkel Cell Carcinoma Symptoms

Merkel cell carcinomas are common on areas of the skin that is exposed to the sun but they could occur anywhere else on the body. In some occasions, the skin above the tumor breaks open and bleeds.

Characteristic features of the nodule are:

  • A round bump that is either red, purple, or pink in color
  • Hardened and firm
  • Painless
  • Rough
  • Raised or dome-shaped
  • Grows rapidly in a short period of time

Some individuals mistake the bumps as a cyst, pimple, or a bug bite and come into a conclusion that it is harmless. If there is a hardened patch on the skin that matches the characteristics of mark cell carcinomas, an appointment to the dermatologist should be made right away.

Causes & Pathology

Scientists are still doing their studies on the exact causes of Merkel cell carcinoma and it is not very clear as to what really causes the condition. Back in 2008, researchers had discovered a virus called Merkel cell polyomavirus (MCPyV) that is often involved in about 80% of MCC tested. The virus is thought to have caused gene mutations that led to Merkel cell carcinoma when the immune system is defective.

Other risk factors that could trigger the disease include:

  • Ultraviolet radiation – It has become a factor of MCC due to the appearance of the tumor on sun exposed skin.
  • Immune system function – People with weakened immune system are much more prone to developing MCC.
  • Certain medications – Drugs that lessens the functioning of the immune system.
  • Having a history of other cancers

Staging

  • Stage 0: The tumor is localized in one position and is negative by pathologic exam.
  • Stage IA: Tumor is approximately 2cm or less and is not visible in any clinical examination.
  • Stage IB: Tumor is equal to or less than 2cm and is not seen in a clinical examination.
  • Stage IIA: Tumor is bigger than 2cm and is not perceivable in a pathologic examination.
  • Stage IIB: Tumor is bigger than 2cm and is not seeable in a clinical examination.
  • Stage IIC: Primary tumor affects the fascia, bone, cartilage, or muscle and the cancer is not seen anywhere near the lymph nodes or distant organs.
  • Stage IIIA: Primary tumor can be of any size and could possibly grow to other tissues close by. Cancer had spread to lymph nodes that are too small to be detected by tests.
  • Stage IIIB: Primary tumor can be of any size and could possibly grow to other tissues close by. Cancer has spread to lymph nodes or has affected a nearby lymph node without entirely reaching the lymph nodes.
  • Stage IV: Primary tumor can be of any size and could possibly grow to other tissues or lymph nodes nearby. Cancer has metastasized.

sentinel lymph node biopsy merkel cell carcinoma


Image 3 – Staging of merkel cell cancer

Treatment

Treatment options for Merkel cell carcinoma may involve:

Surgery

A complete removal of the tumor and the normal skin around it through surgery is the main treatment for primary Merkel cell carcinoma. If the cancer had metastasized to the lymph nodes where the tumor is found, those lymph nodes should also be removed.

Radiation Therapy

Treatment involves the use of high-energy beams at cancer cells. This option is occasionally used after a surgical procedure in order to destroy any remaining cancer cells. Radiation can also be a solo treatment for some.

Chemotherapy

This makes use of certain drugs administered orally or injected through a vein to destroy cancer cells. This is usually recommended if MCC had metastasized to other organs or lymph nodes or if the cancer recurred despite treatment.

Prognosis

MCC is an aggressive cancer that could return back after treatment that is why follow-up appointments with the physician are very essential.  On a positive note, researchers have made generalizations that those patients who have no lymph node cancer have an excellent prognosis. Stage I, II, or III patients have the tendency to do better compared to patients who have the cancer spread beyond the lymph nodes.

Survival Rate

The survival rates are based on when the cancer was first diagnosed only. The overall 5-year survival rate is approximately 60%.

The 5-year survival rates based on staging:

  • Stage IA: about 80%
  • Stage IB: about 60%
  • Stage IIA: about 60%
  • Stage IIB: about 50%
  • Stage IIC: about 50%
  • Stage IIIA: about 25%
  • Stage IV: about 20%

Pictures

merkel cell carcinoma on upper lip

merkel cell cancer on head

merkel cell carcinoma on hand

merkel cell cancer final staging over head

Image Sources www.aboutcancer.com, unotoda.tumblr.com, www.aad.org

References:

  1. Frequently Asked Questions about Merkel Cell Carcinoma – What is merkel cell, Radiation, Scans, Chemotherapy, Metastasis, Research and Support at http://www.merkelcell.org/faqs/index.php
  2. Merkel Cell Carcinoma Symptoms, Causes, Tips at https://www.aad.org/dermatology-a-to-z/diseases-and-treatments/m—p/merkel-cell-carcinoma
  3. Merkel Cell Carcinoma  Statistics, Survival Rate, Coping, Insurance at http://www.cancer.org/cancer/skincancer-merkelcell/
  4. Kwun HJ, Shuda M, Feng H, Camacho CJ, Moore PS, Chang Y (2013 Aug 14). Merkel cell polyomavirus small T antigen controls viral replication and oncoprotein expression by targeting the cellular ubiquitin ligase SCFFbw7. Cell Host Microbe. 14(2):125-35.
  5. Kim JA, Choi AH (2013 Jul). Effect of radiation therapy on survival in patients with resected Merkel cell carcinoma: a propensity score surveillance, epidemiology, and end results database analysis. JAMA Dermatol. 149(7):831-8.
  6. Busam KJ, Jungbluth AA, Rekthman N, et al (2009 Sep). Merkel cell polyomavirus expression in merkel cell carcinomas and its absence in combined tumors and pulmonary neuroendocrine carcinomas. Am J Surg Pathol. 33(9):1378-85.

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