Axillary lymph nodes are the most important prognostic indicator for survival in breast cancer. Our mathematical model suggests the daily increased risk of axillary metastases due to treatment delay is 0.028% for tumors with moderate doubling times of 130 days and 0.057% for tumors with rapid doubling times of 65 days. This minimal maternal risk may be acceptable to some third-trimester pregnant women with early breast cancer, who prefer organ-sparing treatment with radiation after delivery to a mastectomy during pregnancy. This model further quantitates the increased risk of mortality borne by pregnant women whose breast cancer diagnosis is delayed.

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