Tumors are constantly interacting with the surrounding tissue. Usually, the tumor tissue is also spotted with normal, non-transformed cells. Such non-tumorous tissue parts compose what is called the stroma. A working group headed by Dr. Margareta Müller is investigating the molecular mechanisms of interaction between tumor and stroma in order to gain a better understanding of the growth and spread of tumors. It has become increasingly apparent that not only changes in the tumor cells themselves are relevant for tumor development, but also influences from the stroma. Various cells types such as connective tissue cells, inflammation cells, precursor cells and vessel cells get activated. By releasing growth factors and forming blood vessels, stroma cells can promote tumor growth. A working group headed by PD Dr. Dirk Breitkreutz is concerned with the interactions between tumor cells and connective tissue structures. Special attention is given to signals of the basal membrane, a connective tissue layer that regulates the growth of skin cells.