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Merkel Cell Carcinoma (MCC), or primary neuroendocrine carcinoma (cancer arising from cells in the skin or the tissues lining organs) of the skin, is an uncommon type of cancer that is classified as a neuroendocrine tumour. Merkel cells are found under the epidermis (top layer of skin), and play a role in touch perception.

Neuroendocrine cancers are a complex group of tumours that develop in the neuroendocrine system, which is responsible for regulating important bodily functions such as heart rate, blood pressure and metabolism. They most commonly develop in the gastro-intestinal tract, pancreas and the lungs; however, they can develop anywhere in the body. These tumours develop from neuroendocrine cells, which are responsible for receiving signals from the nervous system and producing hormones and peptides (small proteins) in response. 

MCC predominantly occur as firm, painless, reddish nodules on sun exposed areas of the skin, such as the face, neck and arms; however, it can develop anywhere on the body.  While it is most commonly diagnosed on the skin, it can also develop in other parts of the body, such as the inside of the nose or the oesophagus. It is one of the most aggressive  types of skin cancer, and is difficult to diagnose.

Treatment 

If MCC is detected, it will be staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body) and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you.

Cancers can be staged using the TNM staging system:

  • T (tumour) indicates the size and depth of the tumour.
  • N (nodes) indicates whether the cancer has spread to nearby lymph nodes.
  • M (metastasis) indicates whether the cancer has spread to other parts of the body.

This system can also be used in combination with a numerical value, from stage 0-IV:

  • Stage 0: this stage describes cancer cells in the place of origin (or ‘in situ’) that have not spread to nearby tissue.
  • Stage I: cancer cells have begun to spread to nearby tissue. It is not deeply embedded into nearby tissue and had not spread to lymph nodes. This stage is also known as early-stage cancer.
  • Stage II: cancer cells have grown deeper into nearby tissue. Lymph nodes may or may not be affected. This is also known as localised cancer.
  • Stage III: the cancer has become larger and has grown deeper into nearby tissue. Lymph nodes are generally affected at this stage. This is also known as localised cancer.
  • Stage IV: the cancer has spread to other tissues and organs in the body. This is also known as advanced or metastatic cancer.

Cancers can also be graded based on the rate of growth and how likely they are to spread:

  • Grade I: cancer cells present as slightly abnormal and are usually slow growing. This is also known as a low-grade tumour.
  • Grade II: cancer cells present as abnormal and grow faster than grade-I tumours. This is also known as an intermediate-grade tumour. 
  • Grade III: cancer cells present as very abnormal and grow quickly. This is also known as a high-grade tumour. 

Once your tumour has been staged and graded, your doctor may recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you. 

Treatment is dependent on several factors, including location, stage of disease and overall health.

Surgery 

Surgery is most often used in patients who have a tumour that hasn’t metastasised (spread to other parts of the body). The procedure itself will vary depending on the location and size of the tumour, but usually involves removing the tumour and a margin of healthy tissue to help prevent recurrence. Your doctor may recommend Mohs micrographic surgery, which takes portions of the cancer in stages and is performed under local anaesthesia. 

In many cases, surgery is used in conjunction with chemotherapy or radiation therapy.  

Radiation therapy 

Radiation therapy, or radiotherapy, uses controlled doses of radiation to damage or kill cancer cells. It can be administered internally or externally. This may be a satisfactory alternative if you are not a suitable candidate for surgery. This treatment can also be used in addition to surgery. In some cases, radiotherapy is recommended prior to surgery to shrink the tumour so it’s easier to surgically remove. It can also be recommended after surgery to reduce the risk of cancer recurrence in the future. 

Chemotherapy 

Chemotherapy uses drugs to kill or slow the growth of cancerous cells, while minimising the damage to healthy cells. It is usually administered directly to the veins (intravenously), however in some cases in can be administered orally. You may receive a single chemotherapy drug, or a combination, depending on your individual factors. It is usually done in cycles of treatment sessions and periods of rest and can last several months. Chemotherapy can be recommended for patients prior to surgery in order to shrink the tumour, making it easier to surgically remove. In some cases, it can also be recommended after surgery to reduce the risk of cancer recurrence, or if your tumour is advanced and has metastasised.  

Immunotherapy

Immunotherapy is a treatment option that aims to enhance the immune system to fight cancer cells. The immune system is a network of cells, tissues, chemicals and organs that recognises abnormal cells in the body and then attacks them so it doesn’t harm the body. This process is also known as an immune response. Cancer cells are able to prevent an immune response, usually by either setting up barriers so immune cells can’t recognise them, or by constantly mutating to avoid being detected. 

There are four primary types of immunotherapies that may be used to help the immune system provide an immune response:

  • Checkpoint inhibitors, which are the most common type of immunotherapy. These drugs work to inhibit the growth of the cancer cell barriers.
  • Immune stimulants, which help to stimulate and reactivate the immune system to fight the cancer cells.
  • CAR T-cell therapy (chimeric antigen receptor T-cell therapy), which boosts the ability of white blood cells (specifically T-cells) to fight cancer cells.
  • Oncolytic virus therapy, which uses genetically altered viruses to target and attack cancer cells.

Ask your doctors about the availability of immunotherapies and whether you are suitable, as well as any benefits, risks and potential complications that may arise.  

Clinical trials 

Clinical trials are research studies performed to test new treatments. They present the opportunity for people, particularly those with rare or complex cancers, to receive very new treatments which are not yet available otherwise. While these studies have the potential to develop more treatment options, the risk of side effects can be high and are not always known. These trials might involve targeted therapies (to target only the cancer cells), hormonal therapies or immunotherapies.

Clinical trials are often conducted in phases:

  • Phase 0: these trials are used to determine how the body will react to experimental drugs. They are given in very small doses to very few people.
  • Phase I: these trials are used in slightly bigger groups (20-80 people) to determine the safety of the drug, as well as any potential side effects that may arise.
  • Phase II: these trials are used in larger groups (several hundred people) to further evaluate the safety of the drug, as well as whether it is working as it should be.
  • Phase III: these trials are used in groups of several hundred to several thousand people. They are used to monitor any adverse effects of the drug, as well as compare it to other conventional or experimental treatment methods.
  • Phase IV: these studies test the drug in the general population to determine any long-term adverse effects, as well as potential usage in treatment of other conditions. 

Ask your doctors about the availability of clinical trials and whether you are suitable, as well as any benefits, risks and potential complications that may arise.  

Palliative care 

Palliative care aims to improve the patient’s quality of life and alleviate symptoms, without trying to cure the disease. This option is beneficial for patients with advanced MCC at any stage of treatment, not just towards the end of life. It can also be used in conjunction with other treatment options, such as surgery, radiotherapy and chemotherapy, with the intention of relieving pain, alleviating symptoms and meeting your physical, emotional, cultural and spiritual needs. 

Risk factors

The risk factors for MCC include:

  • Being over 50 years of age.
  • Being male.
  • Having a fairer skin colour.
  • Overexposure to the sun/ultraviolet light.
  • Having Merkel cell polyomavirus.

Not everyone with these risk factors will develop the disease, and some people who have the disease may have none of these risk factors. See your general practitioner (GP) if you are concerned.

Early symptoms

MCC is often misdiagnosed, as it may look like many other types of skin cancer. MCC presents as:

  • Red, purple or skin coloured.
  • Painless lump or 'nodule' under the skin.
  • Fast-growing.

Not everyone with the symptoms above will have cancer but see your general practitioner (GP) if you are concerned.

Diagnosis/diagnosing

MCC is difficult to diagnose. If your doctor suspects you have MCC, they will order a range of diagnostic tests. 

Imaging & blood tests 

The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), x-ray, and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and look for signs of metastasis. Additionally, a blood test may be taken to assess your overall health and help guide treatment decisions. 

Biopsy 

Once the location(s) of the cancer has been identified, the doctor will perform a biopsy to remove a section of tissue using a needle. The tissue sample will then be analysed for cancer cells. 

Prognosis (Certain factors affect the prognosis and treatment options)

While it is not possible to predict the exact course of the disease, your doctor may be able to give you a general idea based on rate and depth of tumour growth, susceptibility to treatment, age, overall fitness and medical history. However, because there are so few cases of MCC, it may be difficult to receive an accurate prognosis. Some patients live a long time, even without treatment, while others who receive treatment may have a more aggressive and metastatic tumours. It is very important to discuss your individual circumstances with your doctor to better understand your prognosis.  

References

Some references are to overseas websites. There may be references to drugs and clinical trials that are not available here in Australia.