In addition to its well-recognized role in neurodegeneration, tau participates in maintenance of genome stability and chromosome integrity. In particular, peripheral cells from patients affected by frontotemporal lobar degeneration carrying a mutation in tau gene (genetic tauopathies), as well as cells from animal models, show chromosome numerical and structural aberrations, chromatin anomalies, and a propensity toward abnormal recombination. As genome instability is tightly linked to cancer development, we hypothesized that mutated tau may be a susceptibility factor for cancer. Here we conducted a retrospective cohort study comparing cancer incidence in families affected by genetic tauopathies to control families. In addition, we carried out a bioinformatics analysis to highlight pathways associated with the tau protein interactome. We report that the risk of developing cancer is significantly higher in families affected by genetic tauopathies, and a high proportion of tau protein interactors are involved in cellular processes particularly relevant to cancer. These findings disclose a novel role of tau as a risk factor for cancer, providing new insights in the various pathologic roles of mutated tau.Significance: This study reveals a novel role for tau as a risk factor for cancer, providing new insights beyond its role in neurodegeneration. Cancer Res; 78(13); 3731-9. ©2018 AACR.