We found that the proportion of breast cancers that were pathologic stage IIB or higher increased significantly during the pandemic compared to what would have been expected based on pre‐pandemic trends (+4.02%, 95% CI 1.07–6.97; p = 0.01), as well as the proportion of breast cancers that were ER‐negative (+3.57%, 95% CI 0.87–6.28; p = 0.01) and triple‐negative (+3.55%, 95% CI 0.95–6.15; p = 0.01). Here, ESR1 is linked to breast cancer.