The evolution of the p53-network has not been resolved yet. In vertebrates p53 acts as a crucial tumor suppressor and transcription factor, which controls genome integrity and regulates genes, leading to apoptosis, cell cycle arrest and senescence. P53-homologs have been found in many invertebrates as well. However, most of them seem to exhibit a higher similarity to the vertebrate p63 gene. The genome of Trichoplax adhaerens, the so far only described species within the phylum Placozoa (new molecular data support a species-rich phylum, however), encodes for a p53-homolog with high sequence similarity to human p53 gene. Its basal position in the metazoan Tree of Life, the animals’ most simple bauplan and its rich gene endowment make Trichoplax a promising model organism in the field of cancer research. As yet, little is known about the Trichoplax p53-homolog, however. Therefore, genomic, transcriptomic and ETS data of different placozoan haplotypes will be analyzed by bioinformatics to elucidate the gene/protein structure of p53 and respective binding sites of possible interaction partners. Deep phylogenetic analysis will help to clarify the evolution of p53 among the Placozoa and within the Metazoa.