From its early appearance as an experimental model the fruitfly Drosophila melanogaster has been used to study the progression of cancer. Already some of the first fly mutants isolated from nature showed aberrant cell growth and in recent decades tumors were induced using molecular genetics. This has led to the identification of signaling pathways that are activated in the presence of tumors. We and others found that stress and innate immunity signaling is induced in tumorous fly larvae. Some of these reactions lead to apoptosis of tumor cells while we find they can also contribute to limiting the damage that is associated with tumor growth. These findings increase our understanding of tumor progression and may help to fine-tune tumor therapy.