PRL and breast cancer: The associations of PRL levels with other known breast cancer risk factors, including: age at menarche and first birth, benign breast disease, and adult body weight, have mostly been null for both pre- and postmenopausal women, even after adjusting for parity (Kwa et al, 1976, 1981; Wang et al, 1988; Tworoger et al, 2006a; Eliassen et al, 2007; Su et al, 2009).