Skin cancer: Sunlight also promotes metastases

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MunichBlack skin cancer is particularly treacherous - it quickly forms fatal daughter tumors (metastases) in the lungs, liver or brain. Sunlight is not only the main cause of what is known as malignant melanoma, UV radiation also promotes the spread of cancer cells in the body. The inflammatory reaction of the skin after sunburn plays a key role in this, found a US-German research team.

Migration along the bloodstream

The scientists used mice suffering from skin cancer as the object of investigation. "Again and again we have discovered more melanoma metastases in the lungs of UV-irradiated animals," reports Evelyn Gaffal from the University of Bonn, one of the main authors of the study. In tissue sections, the researchers observed that the cancer cells moved like tiny spiders on the blood vessels and thus quickly reached the organs. Scientists describe the spread of tumor cells along the vessel walls as angiotropism.

Alarm signals from the skin

This process is apparently promoted by inflammatory processes in the skin. At the beginning of the fateful chain of reactions there is an alarm signal (HMGB1), which the UV-damaged cells in the skin send out. This attracts certain immune cells, granulocytes, which are supposed to repair the damage caused - an inflammatory reaction occurs. And it is precisely this, actually healthy, process that apparently supports the cancer cells' migration: their mobility increases.

Hike on old paths

The tumor cells use a mechanism that was originally important during embryonic development: with its help, the precursors of the pigment cells migrated along the blood vessels into the skin. The granulocytes apparently reactivate this mechanism, which had actually been switched off, and the cancer cells take the same route - only in the opposite direction.

Double the risk from sunlight

The study thus shows that sunlight is doubly risky - first through the damage to the genetic material and then through the promotion of metastases. Sunbathing is particularly dangerous when the first skin cells have already deteriorated.

The elucidation of the mechanism could in the future help to develop therapies that at least block the formation of metastases - because it is from these that patients ultimately die.

2500 skin cancer deaths expected

According to the Robert Koch Institute, around 20,000 people in Germany are expected to develop black skin cancer in 2014. More than 2500 affected people will die of daughter tumors in internal organs - the so-called metastases. (cf)

Source: Evelyn Gaffal & Thomas Tüting et al .: Ultraviolet radiation-induced inflammation promotes angiotropism and metastasis in melanoma, Nature, DOI: 10.1038 / nature13111

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