We show that simultaneous deletion of the RAD54L and RAD51AP1 genes further sensitizes human cancer cell lines to treatment with the DNA inter-strand crosslinking agent mitomycin C (MMC), to prolonged exposure to replication stalling by hydroxyurea (HU), and to Poly (adenosine 5′-diphosphate-ribose) polymerase inhibition (PARPi). The gene discussed is RAD54L; the disease is cancer.