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.
Treatment options for MCC may include:
- Surgery, potentially including Mohs micrographic surgery.
- Radiation therapy.
- Chemotherapy.
- Immunotherapy.
- Clinical trials.
- Palliative care.
For more information on treatment options, please refer to the Rare Cancers Australia Treatment Options page.
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.