TNF and melanoma: With the same initial conditions as before and  small but positive, the deterministic system is attracted to the stable fixed point : the T-cell population, , increases in presence of its target x, TNF-α is secreted, and the differentiated melanoma population shrinks due to killing and switching, the population of dedifferentiated melanoma grows, but is regulated and kept at a low level by the T-cells of type zy.