It is called Mycoplasma pneumoniae and, despite being very simple, this small bacterium with only 680 genes could play a key role in fighting lung cancer, the type of tumor that causes the most deaths each year worldwide: nearly two million. I'researcher Luis Serrano and its team, at the Centre for Genomic Regulation in Barcelona (CRG), have spent years studying this microorganism and genetically modifying it to strip it of its ability to cause disease. Now they want to turn it into a kind of Trojan horse capable of releasing drugs against tumor cells only in the lung.