Merkel cell carcinoma: symptoms, diagnosis and treatment

Merkel cells sit in the top layer of the skin, the epidermis, near nerve endings, and help us respond to touch. Cancer Research UK explains that they are a type of neuroendocrine cell, so MCC is classified as a neuroendocrine carcinoma of the skin. It is quite rare compared with basal cell carcinoma, squamous cell carcinoma and melanoma.

Because it is rare, Cancer Research UK says your treatment team should include doctors with experience of looking after people with MCC. A team of doctors and other skin cancer specialists, a multidisciplinary team, discuss the best treatment.

Cancer Research UK says MCC usually appears as a lump on the skin. The lump is often blueish purple (violet) or red, the skin over it is usually firm and not broken, and it does not hurt. MCCs are often found on the areas of the body that get the most direct sun: the head, neck, arms and legs.

Because it is painless, a lump can be easy to dismiss. The NHS describes the main symptom of non-melanoma skin cancer as a growth or unusual patch on the skin, which can vary in colour, size and texture, and notes that patches may be darker on brown or black skin.

Unlike the most common types of skin cancer, Cancer Research UK says MCC develops rapidly over weeks or months. It can spread to other parts of the body such as the lymph nodes, lungs, liver or bones. This is why a lump that is growing should be looked at promptly.

The NHS says it is important to get any symptoms of non-melanoma skin cancer checked by a GP, and that finding skin cancer early can mean it is easier to treat. Its advice is to see a GP if you have:

• a growth on your skin that is getting bigger or has changed colour or texture

• a growth or area of skin that hurts, itches, bleeds, crusts or scabs for more than 4 weeks

• a new or unusual mark on your skin that has not gone away after a few weeks (NHS advice for melanoma, which also applies to any new mark)

The NHS says the GP will look at the affected area and may ask if they can take a photograph to send to a skin specialist (dermatologist). Tell them if the growth has changed recently and if you or your family have had skin cancer before.

If the GP thinks your symptoms could be cancer you may get an urgent referral for more tests or to see a specialist in hospital. The NHS stresses that this does not definitely mean you have cancer.

Cancer Research UK says many people start by seeing their GP, who assesses the symptoms, examines the area and decides whether to refer to a dermatologist. The dermatologist examines the skin and lymph nodes and might look closely at the lump with a dermatoscope. The main test is a biopsy, a sample of skin sent to the laboratory for a pathologist to examine, usually done under local anaesthetic.

If MCC is confirmed, further tests check whether the cancer has spread, such as an ultrasound, CT or PET-CT scan or MRI. The lymph nodes may be checked by ultrasound and biopsy, or with a sentinel lymph node biopsy, in which the first lymph nodes the cancer can reach are removed and examined, done under general anaesthetic at the same time as surgery to remove the MCC.

Cancer Research UK says long-term exposure to sunlight increases the risk and that the risk is higher for white people with fair skin than for Black people. Other factors it lists include ultraviolet light and PUVA treatment for conditions such as psoriasis, conditions or treatments that weaken the immune system, including organ transplant, AIDS and chronic lymphocytic leukaemia, and a virus called Merkel cell polyomavirus.

Age is a risk factor, as with most cancers. The median age at diagnosis is around 76 years, and MCC is more common in men.

Doctors usually use the TNM system, for tumour size, nodes and metastasis, to stage MCC. Cancer Research UK describes tumour categories from T1, 2cm or less, to T4, where the cancer has grown into nearby tissues such as bone, muscle or cartilage, node categories N0 to N3 and metastasis M0 or M1.

Staging helps decide the best treatment and gives an idea of outlook. Your prognosis depends on the stage, and the charity notes that older people tend to have a worse outlook and women a better prognosis than men.

Cancer Research UK says treatment depends on where the MCC started and its size, whether it has spread and your general health and well-being. Surgery is the main treatment: a wide local excision removes all the cancer cells and a small amount of healthy tissue, with a pathologist checking that there is a margin of clear tissue. Lymph nodes may be removed if cancer cells are likely to be there.

Radiotherapy may be given after surgery to kill any cells that may have been left behind, usually once a day, Monday to Friday, for over 5 weeks, or used as the main treatment if surgery is not possible. For MCC that has spread, treatment will not get rid of the cancer but can control symptoms. Immunotherapy with avelumab, given as a drip every 2 weeks, and chemotherapy are options.

NICE has published technology appraisal guidance on avelumab (Bavencio) for metastatic Merkel cell carcinoma, TA517, published in April 2018 and updated in April 2021.

Cancer Research UK says the best person to talk to about your outlook (prognosis) is your doctor, and that survival depends on many factors, so no one can say exactly how long you will live. Not everyone wants to know, and people cope differently.

It says your prognosis depends on the stage of your MCC and where it started, and that other factors include age and sex: older people tend to have a worse outlook and women a better prognosis than men.

After treatment Cancer Research UK says you usually have appointments every 3 months for the first 3 years and then every 6 months for up to 5 years, with an examination and sometimes scans. You can raise concerns at any visit.

Coping with a cancer diagnosis can be difficult. The charity notes that being well informed about your cancer and its treatment can make it easier to make decisions and cope.

On the NHS, suspected skin cancer is referred urgently through a GP, and Cancer Research UK says treatment is discussed by a multidisciplinary team of skin cancer specialists that should include doctors with experience of MCC. NHS treatment is free at the point of use.

Some people seek private dermatology for faster assessment or a second opinion, and then continue treatment in the NHS system. The treatment decisions are made on the same factors of stage, site and fitness.