@article{Ma2006,
author = {Ma, H. and Bernstein, L. and Pike, M.C. and Ursin, G.},
title= {Reproductive factors and breast cancer risk according to joint estrogen and progesterone receptor status: a meta-analysis of epidemiological studies},
year = {2006},
doi = {10.1186/bcr1525},
journal = {Breast Cancer Research},
volume = {8},
number = {4},
pages = {1--11},
}