Endocytic tumour suppressor genes such as Rab5, the syntaxin Avalanche (Avl) and the Rab5 effector Rabenosyn-5 (Rbsn-5), act at the level of early endosome fusion (Gorvel et al., 1991; Lu and Bilder, 2005; Morrison et al., 2008; Nielsen et al., 2000). The gene discussed is RAB5A; the disease is neoplasm.