Merkel’s Carcinoma

Merkel’s cells carcinoma (MCC), also called neuroendocrine skin carcinoma, is a type of skin cancer that occurs when skin cells grow uncontrollably. The tumor usually presents as a single reddish or purple lump on a part of the skin that is usually exposed to sunlight, such as face, neck, or arms.

This is a rare disease that affects mostly white people over 70 years old.

Merkel’s cells are believed to be a type of neuroendocrine skin cell, because they share some characteristics with nerve cells and hormone-producing cells. They are mainly found at the base of the top skin layer, the epidermis, and are in close proximity to skin nerve endings.

Signs and symptoms of Merkel’s carcinoma

Merkel’s carcinoma starts mainly on sun-exposed areas of the skin, such as the face, neck, and arms, but it can occur anywhere on the body. It often first appears as a single bright pink, red, or purple lump, which usually does not hurt. Skin on top of the tumor may split and bleed.

These rapidly growing tumors can spread as new lumps on nearby skin. They can also reach the lymph nodes, which over time grow and become visible or are felt as lumps under the skin (usually on the neck or under the arm).

Because they are rare, look like other more common types of skin cancer, or even skin problems that are not cancer, doctors are unlikely to suspect MCC at first, and diagnosis is usually made only after a biopsy.

It is therefore very important that any lumps, new or growing spots are examined promptly by a dermatologist.

Merkel’s carcinoma diagnosis

If the patient presents an abnormal area that may be skin cancer, doctors will examine and run tests to find out if it’s cancer or some other issue. If MCC is diagnosed and there is a risk that it has spread to other body parts, further tests will be necessary.

Along with a standard physical exam, some dermatologists use a technique called dermatoscopy to evaluate different skin lesions more clearly. The doctor uses a dermatoscope, which is a special magnifying lens with a light source, close to the skin.

If MCC or other skin cancer is suspected, a small piece of the lesion will be removed and sent to a laboratory for testing – this is called a biopsy.

There are different ways to perform a skin biopsy. The choice is made based on the suspected type of skin cancer, where it is in the body, its size, and other factors.

Skin biopsies are done with a local anesthetic, and the main types are:

• Tangential biopsy – the upper layers of the skin are scraped with a small surgical blade. It is useful in diagnosing many types of skin diseases, especially if the doctor feels that an abnormal area is unlikely to be a serious skin cancer, such as MCC or melanoma. It is usually not used if the doctor strongly suspects MCC or melanoma, because this technique is not deep enough to reach the tumor;
• Punch biopsy – a tool that looks like a small round cookie cutter is used to remove a deeper sample of skin. The doctor rotates the punch biopsy tool on the skin until it cuts through all the required layers. The sample is removed and the edges of the biopsy site are closed;
• Incisional and excisional biopsies – used to examine a tumor that may have grown into deeper layers of the skin. For these types of biopsies, a surgical scalpel is used to cut through the full thickness of the skin, removing a wedge or piece of skin. Incisional biopsy removes only part of the tumor, while excisional biopsy removes the entire tumor and tends to be preferable for a suspected MCC;
• Lymph node biopsy – MCC can spread to nearby lymph nodes early on. If the tumor has already been diagnosed in the skin, nearby lymph nodes will usually be biopsied to see if the cancer has reached them. The type of biopsy used depends on the likelihood that the cancer has reached nearby lymph nodes; and
• Sentinel lymph node biopsy (SLNB) – a sentinel lymph node biopsy can be used to locate the lymph nodes that would likely be the first place the MCC would go if the tumor has spread.

If, when analyzing the samples, the pathologist cannot determine that MCC exists, special laboratory tests can be performed on the cells to confirm the diagnosis.

One of the commonly used tests for MCC is immunohistochemistry (IHC), which looks for certain proteins in the cancer cells, such as CK-20, CK-7, neuro-specific enolase, TTF1, and S100.

With MCC being found, the pathologist will also examine important features, such as thickness of the tumor, the portion of cells that are actively dividing (mitotic rate), and whether the tumor has invaded the tiny blood vessels or lymphatic vessels in the specimen.

Imaging tests, which use X-rays, MRI, or CT scans to create images from inside the body, can be done to see if MCC has spread to lymph nodes or to other organs. They may also be done to help check whether treatment is working well or to look for possible signs of cancer returning (recurrence) after treatment has ended.

Learn more about the main imaging tests performed to diagnose Merkel carcinoma:

• Computed tomography (CT) – can show details in soft tissues (such as internal organs), whether lymph nodes are enlarged, or whether other organs have suspicious staining (which may be from the spread of MCC). It also helps guiding a needle biopsy;
• MRI – is very useful in detecting cancer that has spread to brain and/or spinal cord; and
• Positron emission tomography (PET) scan – can help show if the cancer has spread to the lymph nodes or other parts of the body. It looks for areas where cells are growing rapidly (which can be a sign of cancer), rather than just showing if areas look abnormal based on their size or shape.

Treatment

• Surgery is the main treatment for most Merkel’s cells carcinomas. Different types can be done:
• Wide excision – when a diagnosis of MCC is made by skin biopsy, the tumor site will likely need to be surgically cut out (excised) to help ensure that the cancer has been removed completely. This surgery can cure this type of cancer if it has not spread beyond the skin;
• Mohs micrographic surgery – used when the goal is to save as much healthy skin as possible, such as cancer around the eye. Using Mohs technique, the surgeon removes the tumor and a margin of normal-looking skin and examines it under a microscope. If cancer cells are seen at the edges of the removed tissue (the sample), another layer of skin is removed and examined. This is repeated until the skin samples contain no cancer cells;
• Lymph node dissection – if cancer is found in nearby lymph nodes, a lymph node dissection is usually performed. In this operation, the surgeon removes all the lymph nodes near the primary tumor – for example, if Merkel’s carcinoma is found in one arm, the surgeon will remove the lymph nodes in the axillae (armpits) on that side of the body, as these nodes are where cancer cells would be most likely to reach first; and
• Skin grafting and reconstructive surgery – after removing large skin cancers, it may not be feasible to stretch the skin close enough to stitch the edges of the wound and cover the entire area. In these cases, healthy skin can be taken from another part of the body and grafted over the exposed region to help with healing and improve the appearance.

There is no consensus on how radiation therapy should be used for Merkel’s cells carcinoma, but it is known that it can be used in the following situations:

• To treat the main (primary) skin tumor area after surgery, trying to kill any cancer cells that may have been left behind;
• To treat the main tumor, if surgery is not an option (due to the person not being healthy enough or the tumor being in a place where it cannot be completely removed);
• To treat lymph nodes near the main tumor;
• To help treat MCC that has come back after surgery, either on skin or in lymph nodes; and
• To help treat MCC that has spread to distant parts of the body, usually along with other treatments.

Chemotherapy is most useful for MCC that has spread to other organs, and so far it is unclear whether it can be useful for cancers that are still only in the skin or have reached only nearby lymph nodes. Even so, some doctors may still recommend chemotherapy to treat this disease. These are drugs administered by IV or orally that travel through the bloodstream to all parts of the body.

Finally, immunotherapy is a promising new alternative treatment for Merkel’s cells carcinoma (MCC), especially if it has spread to other parts of the body. This involves the use of drugs that help the immune system find and destroy cancer cells.

Prevention

Because Merkel’s carcinoma can be caused by sun exposure, some strategies to prevent it are important:

• Avoid excessive sun exposure between 10am and 4pm, when sunlight is at its strongest;
• Do not do chamber artificial tanning;
• Wear protective clothing, such as long-sleeved shirts, pants, and a wide-brimmed hat, especially when you need to be exposed to the sun between 10am and 4pm; and
• Use sunscreen daily, with a minimum sun protection factor (SPF) of 30 and protection against UVA and UVB rays, reapplying every two hours and/or after swimming or perspiring.

Other known, non-controllable risk factors include:

• Being over 50 years old;
• Being light-skinned; and
• Having a compromised immune system, which includes people with HIV, multiple myeloma, melanoma or chronic leukemia, and people taking immunosuppressive medications.