Breast cancer during pregnancy: Quantifying the risk of treatment delay

Objective: To quantify the risk of axillary nodal metastases due to delayed treatment of breast cancer during pregnancy. Methods: A mathematical model using recently published data was developed to correlate primary breast tumor size with the percentage of pathologically positive axillary lymph nodes. Using this relationship obtained from pathologic data and the accepted relationship of tumor growth and time, Y₂ = Y₁e((ln2)n/DT), an equation estimating the increased risk of axillary metastases due to each day of treatment delay was derived: ΔX = 3.7 n/DT, where X = percent positive axillary lymph nodes, n = number of days delay in treatment, and DT = tumor doubling time. Results: A 1-month delay in treatment for an early-stage primary breast cancer with a 130-day doubling time increases the risk of axillary lymph node involvement by 0.9%. A 3-month delay increases the risk by 2.6%, and a 6-month delay by 5.1%. For breast cancer with a 65-day doubling time, a 1-month delay increases the risk by 1.8%, a 3-month delay by 5.2%, and a 6-month delay by 10.2%. Conclusion: 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.