Among the 297 up‐regulated proteins in the hippocampus of mice that experienced spontaneous mammary tumour regression (compared to CANReject mice) were neuronal and synaptic plasticity‐associated proteins, including synaptogyrin‐1 (Syngr1), synaptogyrin‐3 (Syngr3), synaptoporin (Synpr), synaptophysin (Syp), neuritin‐like protein (Nrn1), neurogranin (Nrgn), synaptosomal‐associated protein 25 (Snap25) and neural cell adhesion molecule (Ncam1). Here, NRN1 is linked to breast cancer.