['The contralateral unaffected breast (CUB) of women with unilateral breast cancer provides a model for the study of breast tissue-based risk factors. Using random fine needle aspiration (rFNA), we have investigated hormonal and gene expression patterns related to atypia in the CUBs of newly diagnosed breast cancer patients.', '83 women underwent rFNA of the CUB. Cytologic analysis was performed using the Masood Score (MS), atypia was defined as MS\xa0>\xa014. RNA was extracted using 80% of the sample. The expression of 20 hormone related genes was quantified using Taqman Low Density Arrays. Statistical analysis was performed using 2-tailed t tests and linear regression.', 'Cytological atypia was more frequent in multiparous women (P\xa0=\xa00.0392), and was not associated with any tumor-related features in the affected breast. Masood Score was higher with shorter interval since last pregnancy (R\xa0=\xa00.204, P\xa0=\xa00.0417), higher number of births (R\xa0=\xa00.369, P\xa0=\xa00.0006), and estrogen receptor (ER) negativity of the index cancer (R\xa0=\xa0-0.203, P\xa0=\xa00.065). Individual cytologic features were associated with aspects of parity. Specifically, anisonucleosis was correlated with shorter interval since last pregnancy (R\xa0=\xa00.318, P\xa0=\xa00.0201), higher number of births (R\xa0=\xa00.382, P\xa0=\xa00.0004), and ER status (R\xa0=\xa0-0.314, P\xa0=\xa00.0038). Eight estrogen-regulated genes were increased in atypical samples (P\xa0<\xa00.005), including TFF1, AGT, PDZK1, PGR, GREB1, PRLR, CAMK2B, and CCND1.'] Is cytologic atypia in the contralateral unaffected breast related to parity and estrogen-related genes?