We observed no difference in log-transformed sRANKL and OPG concentrations, or the sRANKL/OPG ratio by ER and/or PR status (negative vs positive; p ≥ 0.11) or by breast cancer stage at diagnosis (localized vs non-localized; p ≥ 0.23), nor did we observe any interaction by cancer stage at diagnosis in our Cox regression models (localized vs non-localized (including regional, distant, and unspecified metastatic sites) breast cancer-specific mortality phet ≥ 0.18; all-cause mortality phet ≥ 0.43). Here, ESR1 is linked to breast cancer.