Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that is characterized by the progressive degeneration of both upper motor neurons in the motor cortex and lower motor neurons in the brainstem and spinal cord. Recent advances in human genetics have identified more than 30 ALS-causing genes or genetic loci that include the fused in sarcoma (FUS) gene. In addition, a set of studies suggested a mutual relationship between cancer and ALS. The hpo gene, Drosophila MST was newly identified as a novel genetic modifier of the cabeza (caz), Drosophila FUS. The Hippo pathway negatively regulates the control of organ growth and tumor suppression. Moreover, the p53 tumor suppressor was found to genetically interact with caz. Frontotemporal lobar degeneration (FTLD) is characterized by the degeneration of neurons in the frontal and temporal lobes, and consists of a spectrum with ALS. Fusion protein nucleophosmin-human myeloid leukemia factor 1 (NPM-hMLF1), which is associated with the pathologies of myelodysplastic syndrome and acute myeloid leukemia, was recently shown to suppress defects in the Drosophila FTLD model expressing the human FUS gene. Further studies in the field are expected to elucidate epidemiological, genetic, and histopathological links between cancer and ALS/FTLD, and will lead to the development of therapeutic strategies. We herein summarize previous and current findings that support mutual links between cancer and ALS/FTLD.