About the Disease / Symptoms & appearance of Merkel cell carcinoma

Symptoms & appearance of Merkel cell carcinoma

Although Merkel cell carcinoma has some visual features that are usually present, it does not have a truly distinctive appearance that allows it to be reliably distinguished from less dangerous skin lesions or other skin cancers.

Appearance of Merkel cell carcinoma

MCC usually develops on sun-exposed skin (e.g., head, neck, arms) as a painless, firm bump that can be red-purple or skin-colored. Patients frequently point out a new MCC to their doctor because a bump is growing rapidly and/or does not look like anything the patient has ever had before.  Most MCCs are diagnosed when a skin biopsy biopsy The removal of cells or tissue in order to determine the presence, characteristics, or extent of a disease by a pathologist usually using microscopic analysis. is performed to rule out another sun-induced skin cancer cancer A term used to describe diseases in which abnormal cells continually divide without normal regulation. Cancerous cells may invade surrounding tissues and may spread to other regions of the body via blood and the lymphatic system. or to remove a presumed cyst. In the vast majority of cases, both the doctor and the patient are surprised by the diagnosis of MCC.

Picture of a Merkel cell carcinoma arising on the fifth digit of the left hand.
Picture of a Merkel cell carcinoma arising on the fifth digit of the left hand.

See the Clinical Photos page for more examples of MCC.

How does MCC differ in appearance from melanoma?

Unlike malignant malignant Having the ability to grow without normal regulation, to invade local tissues aggressively and/or spread throughout the body. melanoma melanoma A form of skin cancer that begins in melanocytes (the skin cells that produce the pigment melanin). Melanoma affects about 42,000 Americans per year and has about a 15% mortality. , MCC is essentially never dark brown or black.

A characteristic malignant melanoma is shown with its brown-black colors. MCC does not ‘pigment’ like this.

How does an MCC differ in appearance from a squamous cell carcinoma?

Unlike a squamous cell carcinoma squamous cell carcinoma Squamous cell carcinoma is a cancer that begins in squamous cells, which are thin, flat cells. Squamous cells are located in the middle layers of the epidermis, the lining of portions of the respiratory and digestive tracts, and the lining of some organs. Squamous cell carcinoma affects about 100,000 Americans and has a mortality of roughly 2%. , MCCs are rarely scaly and are rarely ulcerated (have broken skin on top) unless a biopsy has just been carried out.

Squamous cell carcinoma
This squamous cell carcinoma has white scaly/crusty material in some areas, is missing normal skin in other areas, and can sometimes bleed.

Where does MCC occur on the body?

MCC primarily occurs on highly sun-exposed skin such as the head/neck and arms (see the figure below), but it can occur anywhere on the body, including sun-protected areas such as the buttock or the scalp under hair.

Where MCC occurs on the body
Distribution of Merkel cell carcinomas on the skin among 195 patients at the time of diagnosis (Heath, 2008).

Solid circles depict MCC tumors that arose on the skin (86% of these cases). Open circles indicate MCCs that presented in lymph nodes without an associated “ primary lesion primary lesion The abnormal tissue that appeared first. The majority of Merkel cell carcinoma primary lesions occur in sun-exposed areas. In some cases of MCC (approximately 11%) the patient has no primary lesion and instead has a nodal presentation (disease in a lymph node only). In these cases the primary lesion likely was destroyed by the immune system. ” (this was the case in 14% of cases).  Recent data suggest that patients who present without a primary lesion lesion An area of abnormal tissue that may be either benign or malignant. originally did have a lesion on the skin, but that their immune system eliminated the tumor. Elimination of the primary lesion is associated with less risk for patients that already have the same stage stage Physicians determine the stage of cancer by performing physical exams and tests. Stages describe the extent of cancer within the body, especially whether the disease has spread (metastasized) from the primary site to other parts of the body. at presentation (see Disease Stages).

How are MCC tumors measured?

Merkel cell Merkel cell Merkel cells are found in the lower part of the epidermis. Although the exact function of Merkel cells is unknown, they are thought to be touch receptors. Also known as neuroendocrine cells, they have machinery similar to nerve cells and to hormone-secreting (endocrine) cells. carcinomas are measured by their largest dimension, in centimeters. Among 5722 cases, the average Merkel cell carcinoma Merkel cell carcinoma A skin cancer composed of cells that look microscopically similar to normal Merkel cells present in the skin. MCC was first described in 1972 and only in the 1990s was the CK20 antibody developed to make it easily identifiable by pathologists. Many doctors and patients are not aware of this cancer because of its recent description and relative rarity (~2,000 cases/year in the US--roughly 30 times less common than melanoma). About 40% of patients treated for MCC will experience a recurrence, making it far more aggressive than most other types of skin cancer, including melanoma. was 1.7 cm in diameter (a US dime is also 1.7 cm in diameter). Larger MCC tumors are associated with moderately higher risk of recurrence and spread to lymph nodes, but even a very small MCC tumor (under 0.5 cm) still has at least a 15% chance of already having spread to nearby lymph nodes.1

Symptoms of Merkel cell carcinoma

The combination of a rapidly growing bump that may be red or purple yet is painless is a common scenario leading up to the discovery of a Merkel cell carcinoma carcinoma Cancer that originates in the skin or in the tissues lining the gut and ducts. . While a cyst can grow rapidly and is often red-purple, such an “inflamed cyst” will almost always be tender, which is very unusual for a Merkel cell carcinoma.

A Closer Look

A study2 of 195 Merkel cell carcinoma patients was carried out to determine the features that doctors or patients typically find associated with this cancer.  “AEIOU” summarizes the features that are usually associated with MCC. 89% of MCC tumors have three or more of these five features:

A:  Asymptomatic—88% of MCCs are not tender.
E:  Expanding rapidly—63% of MCCs have grown significantly within the past 3 months
I:   Immunosuppression*—MCC patients are 16-times more likely to be immunosuppressed*
O:  Older than 50—90% of MCC patients are over age 50 & MCC risk keeps increasing with age
U:  UV exposed fair skin—81% of MCCs arise on sun-exposed skin and 98% of MCCs arise in people whose skin tone is light

* The relationship between immune suppression & MCC is tricky to understand. While only 8% of MCC patients have severe, long-term immune suppression (such as HIV, leukemia, or a transplanted organ), this is a 16-fold over-representation compared to the general population. Such long-term immunosuppressed patients have a higher risk of developing MCC and of later having their MCC recur.


What does MCC look like?

MCC usually develops on sun-exposed skin as a firm, painless, flesh-colored to red-violet bump. The initial small bump tends to grow rapidly over weeks to months. Some images can be seen on our Clinical Photos page.

Where does MCC occur on the body?

MCC primarily occurs on highly sun-exposed skin such as the head/neck and arms, but it can occur anywhere on the body, including sun-protected areas such as the buttock. Learn more about the symptoms and appearance of Merkel cell carcinoma.

Understand the Science

The following clinical publications and scientific research provide additional in-depth information about the symptoms & appearance of Merkel cell carcinoma.

Clinical characteristics of Merkel cell carcinoma at diagnosis in 195 patients: the AEIOU features.

The first clinical description of Merkel cell carcinoma based on 195 patients in Dr. Nghiem's database is published in the Journal of the American Academy of Dermatology. We define the "AEIOU Features of MCC" which are Asymptomatic (non-tender), Expanding Rapidly, Immune suppression, Older than age ...

Read More