What is Merkel cell carcinoma?

The term Merkel cell carcinoma (MCC) describes a rare and aggressive skin tumour that has a high recurrence rate. The Merkel cell carcinoma often tends to metastasise to the lymph nodes and/or organs and therefore has a high mortality rate. It forms preferentially on parts of the body that are exposed to a lot of light . Light-skinned people over 50 years of age are affected by the disease with above-average frequency. Since Merkel cell carcinoma has a high recurrence rate despite chemotherapy and radiation therapy, the chances of cure are rather unfavourable.

What causes Merkel cell carcinoma to develop?

According to scientific studies, there is a close connection between a Merkel cell carcinoma and intensive UV radiation exposure. In addition, it was found that people with immunosuppression have a 15-fold increased risk of developing Merkel cell carcinoma than people of the same age without immunosuppression. People suffering from immunosuppression, i.e. an immune system that is suppressed for a certain period of time , are for example people with an HIV disease or organ transplant patients.

In addition to these risk factors, scientists have found that many Merkel cell carcinomas can be linked to the so-called Merkel cell polyomavirus . In almost 80 percent of all cases, the Merkel cell polyomavirus could be detected in the tumour tissue . However, since the Merkel cell polymavirus is also found in healthy people, it is suspected that it can trigger the disease together with other factors.

What stages can Merkel cell carcinoma be divided into?

For Merkel cell carcinoma, as for other cancers, the usual classification of tumour stage according to the so-called TNM classification applies. In general, the course of the disease can be described as follows :

Within the first two years after diagnosis of the primary tumour, most metastatic metastases occur. Many Merkel cell carcinomas form daughter tumours via the lymphatic system. For this reason, a so-called sentinel lymph node biopsy (SLNB) is performed after the diagnosis of the primary tumour. In about 30 per cent of all cases of the disease, it turns out that metastases are already present, which significantly worsens the chances of a cure.

How can Merkel cell carcinoma be recognised externally?

The Merkel cell carcinoma appears as an externally smooth, painless lump on the surface of the skin, which has a rough consistency. Merkel cell carcinoma is most common on the head and neck, but also on the arms and legs and is less common on the trunk . It is often a smooth, painful lump on the surface of the skin. Often, these are skin areas that are particularly exposed to light. Typically, Merkel cell carcinoma takes on a reddish, bluish or skin-coloured colour and can vary greatly in size. On average, Merkel cell carcinoma takes on a diameter of about 1.7 centimetres at first diagnosis. This corresponds to about a 10-cent piece, but it grows rapidly.

Under the acronym "AEIOU" , the typical clinical features of Merkel cell carcinoma can be summarised as follows:

• A: asymptomatic,
• E: (rapid) expansion,
• I: immunosuppression,
• O: elderly (older) patients,
• U: UV-exposed skin (localisation)

How is Merkel cell carcinoma diagnosed?

The Merkel cell carcinoma is diagnosed by means of a biopsy. Here either tumour cells are removed or the skin tumour is completely removed and then examined under the microscope for possible cancer cells . If this microscopic examination reveals that it is indeed a Merkel cell carcinoma, the lymph nodes should be examined by ultrasound for a possible metastasis. This is because a Merkel cell carcinoma spreads quickly through the lymph nodes.

In about 20 percent of all initial diagnoses, metastasis to the lymph nodes can be detected. If this is not the case, it is still advisable to surgically remove the lymph node (sentinel lymph node) closest to the primary tumour. Afterwards, a biopsy should also be performed . If this sentinel lymph node is not affected by metastases, this considerably increases the chances of cure: in this case, about 81 percent of all patients are still alive 3 years after diagnosis. If, on the other hand, there is evidence of lymph node involvement, further imaging examinations, such as ultrasound, MRI or CT, are used to determine the extent of the spread of the tumour.

How is Merkel cell carcinoma treated?

The treatment of Merkel cell carcinoma depends on the stage of the disease . As with other cancers, there are three main types of treatment for Merkel cell carcinoma:

• surgical removal of the primary tumour,
• radiotherapy,
• systemic tumour therapy in the form of immunotherapy and/or chemotherapy.

 
In the case of a Merkel cell tumour, an attempt is made, if possible, to remove the tumour completely and with a large safety margin to the healthy tissue . Depending on how early the Merkel cell carcinoma was diagnosed and whether it could be completely removed, the better the chances of cure. If the sentinel lymph node and/or the surrounding lymph nodes are affected, these should also be surgically removed as completely as possible.

Radiation therapy can be administered adjuvantly, i.e. as a supportive measure after surgery, and aims to reduce the risk of the tumour recurring. Any tumour cells that may still be present should be killed by the radiotherapy.

If the disease is already far advanced at the time of diagnosis or if distant metastases are present, surgery followed by radiotherapy usually comes too late. However, in order to still enable the patient to live a life worth living , the immune system of those affected can be stimulated by stimulating antibodies, the so-called checkpoint blockers . If the disease progresses, a chemotherapy can also be useful and be administered as a combination therapy of several chemotherapeutic agents. Although many patients initially usually respond positively to chemotherapy, this effect is usually not long-lasting.

What is the aftercare for Merkel cell carcinoma?

Merkel cell carcinomas tend to form again quickly, which is why close monitoring at intervals of every three months is recommended after a successful treatment. After three years, treatments can take place at half-yearly intervals. In addition to the regular check-ups by the doctor, the patients should, however, examine their skin again and again on their own. It is also advisable to avoid contact with direct UV radiation .