Metastasis forms from tumour cells that originate from a main tumour. These cells have been able to move from the original location of the tumour, and to give rise to secondary tumorous formations called metastasis in any other part of the body. 

These cells are independent of each other and of the tumour from which they derive. They are dangerous because of their intrinsic capacity to transform both, to take advantage of the circulation as a vehicle, and to attach other tissues that have different characteristics from those from which they originate. 

When they are located exclusively under the skin, they are called subcutaneous metastasis, and they appear as lumps with various features: alone or numerous, larger or smaller, hard or soft to the touch, and more or less painful.  Sometimes they affect the lymph nodes, and at other times the layer of adipose panniculus above the muscles.

In such cases, under ultrasound scan guidance, one or more cryoprobes can be inserted into a secondary tumour (or metastasis), for the purpose of burning it up completely. Cryoablation of the tissue triggers an apoptosis mechanism (or the planned and thus controlled cell death) of the mass involved, which will later be reabsorbed by the body. 

The metastasis will disappear leaving a small scar in its place that can often be neither felt nor seen.