Malignant cells when grown in suspension, as a rule, proliferate and can form spheroids that have been used as a model of tumor nodules, micrometastases and avascular tumors. In contrast, normal adherent cells cannot be stimulated to grow as multicellular aggregates. Now, recent results show that normal fibroblasts if forced to cluster (spheroid formation) do not grow but undergo a new pathway of cell activation (nemosis) leading to a massive proinflammatory, proteolytic and growth factor response. The clustering and activation are initiated by fibronectin-integrin interaction. The activated fibroblasts are able to modulate the behavior of cancer cells and, furthermore malignant cells boost this activation even further. In this model, the activation of fibroblasts terminates in programmed necrosis-like cell death. Activation of the tumor stroma, especially of fibroblasts, is of critical importance for tumor progression, although mechanisms leading to their activation are still largely uncharacterized. In summary, our results suggest that this kind of fibroblast activation (nemosis) may be involved in pathological conditions such as inflammation and cancer.