BACKGROUND/AIM NOTCH-regulated ankyrin repeat protein (NRARP) has been implicated in crosstalk between NOTCH and wingless-type mouse mammary tumor virus integration site (WNT) signals during development. Our study aimed to clarify its role in breast cancer cells. MATERIALS AND METHODS Public microarray data were used to analyze gene expression in human and rat breast cancer. A short interfering RNA was introduced into MCF7 and T47D human breast cancer cells for NRARP silencing. Gene expression was analyzed by quantitative polymerase chain reaction. RESULTS The NRARP transcript was commonly overexpressed in various rat mammary cancer models. In addition, a subset of human breast cancer also expressed high levels of NRARP transcript, which correlated positively with up-regulation of cell proliferation-related genes. Silencing of NRARP suppressed the growth of MCF7 and T47D cells and lowered the expression of cell cycle-related genes in MCF7 cells. CONCLUSION NRARP may stimulate cell proliferation in human breast cancer.