CK 20 marker is key to early diagnosis of Merkel cell carcinoma


By Ling Gao, MD, PhD

Merkel cell carcinoma is one of the most deadly forms of skin cancer for several reasons. It grows and spreads very quickly, it behaves differently from other types of cancer, and it lacks well-defined treatment guidelines.

Perhaps most tragically, though, patients die from Merkel cell carcinoma because it is often misdiagnosed as a less-aggressive cancer.

Merkel cell carcinoma is extremely rare. Only about 2,000 cases are diagnosed in the United States each year. However, its incidence has tripled since the late 1990s. This cancer can double or triple in size in a few months. 

In about 50 percent of all cases, the cancer has already spread to the lymph nodes by the time it is diagnosed. After it has been diagnosed, we have limited treatment options. Due to these factors, about half of all patients die within five years of diagnosis.

If patients were diagnosed at an early stage, we’d be much more successful at reducing the mortality rate. However, because Merkel cell carcinoma is so rare, most dermatologists have never seen it in a clinical setting and it’s not even on their radar. Because it is a blue cell tumor, pathologists often misdiagnose it as basal cell carcinoma, which is also a blue cell tumor. Patients sometimes experience multiple biopsies before it’s correctly diagnosed. By that time, it’s usually too late.

Early diagnosis is vital, particularly because treatment options for advance stages of the disease are so limited.

Therefore, it is necessary for dermatologists to become familiar with Merkel cell carcinoma so patients can be diagnosed earlier and receive the most effective treatment. In my role as a physician scientist at the College of Medicine at the University of Arkansas for Medical Sciences Winthrop P. Rockefeller Cancer Institute, I have formed a multispecialty group working with an oncologic surgeon, a medical oncologist, and a radiation oncologist to take care of Merkel cell carcinoma patients using cutting-edge knowledge. 

I am also a member of a national Merkel cell carcinoma interest group, which keeps me up to date with advances in Merkel cell carcinoma research and clinical management.

The finding that the CK 20 marker distinguishes Merkel cell carcinoma from other blue cell cancers has been a major diagnostic advancement. Because of the increased awareness at my institution, pathologists may perform an additional CK 20 stain on tumors so they don't miss a Merkel cell carcinoma.

                Merkel-cell-carcinoma1.jpg Merkel cell carcinoma: This rare skin cancer can appear on the skin as a hard patch (1) or a firm bump (2).

Early diagnosis is vital, particularly because treatment options for advance stages of the disease are so limited. If the tumor hasn’t spread and is less than 2 centimeters, it typically is removed with local incision. Treatment becomes murkier in later stages. 

The most recent guidelines released by the National Comprehensive Cancer Network about treatment of Merkel cell carcinoma state that the most effective treatment is surgery in conjunction with radiation therapy. 

However, not all physicians agree. I’ve worked with radiologists who did not want to treat a Merkel cell tumor with radiation because it was too small and they were concerned about radiation side-effects on the patient. Chemotherapy is sometimes given to patients in stage three or four, but the cancer typically responds poorly to it.

There has been some early success in pre-clinical studies involving immunotherapy. My research involves trying to understand the fundamental changes in cancer cell biology that contribute to the development of cancer, and eventually identifying the potential therapeutic targets for Merkel cell carcinoma. In addition, researchers are investigating the use of certain melanoma drugs to kill the tumors.

However, most treatments are still in the experimental stage. That’s why it’s essential that dermatologists learn more about this deadly disease and recognize it before it advances.

Dr. Gao is an assistant professor in the department of dermatology in the College of Medicine at the University of Arkansas for Medical Sciences (UAMS). As a physician-scientist, she conducts basic research at the UAMS Winthrop P. Rockefeller Cancer Institute and sees patients in the dermatology clinic.  

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