Quantifying Chemotherapy Delivery in Older and Younger Women With Early-Stage Breast Cancer Using Longitudinal Cumulative Dose

Background: Delivery of cancer treatments, such as chemotherapy, requires a complex set of decisions that can change over time. Traditional measures of chemotherapy delivery, such as relative dose intensity, measure the amount of chemotherapy received by the end of treatment but mask the timing of dose reductions, delays, and discontinuation. These events may be important for delivering timely interventions to support adherence and lower the risk of recurrence. Materials and Methods: We used an institutional database to identify women diagnosed with stage I-III breast cancer receiving adjuvant chemotherapy with a standard 4-cycle regimen of docetaxel + cyclophosphamide (TC, every 21 days) from April 2014 to December 2019. LCD was calculated as the amount of a given chemotherapy agent delivered at a specified time, t, divided by the total planned standard chemotherapy dose at time t. We visualized LCD curves for each chemotherapy agent and reported the median LCD and interquartile range (IQR) at the end of the regimen, overall and by age group (<65 years vs. 65+ years). Results: The study population included 80 women. At the end of treatment, overall median LCDs for both cyclophosphamide and docetaxel were 100% (IQR: 99.6%, 100%), suggesting that TC was well tolerated. However, the lower quartile LCD for cyclophosphamide was 98.7% in older women treated with TC compared with 99.7% in younger women. Conclusion: Within our cohort, adjuvant TC was well tolerated with LCD curves showing largely on-time and full-dose administration. Subgroup analyses showed only slight decreases in adjuvant TC LCD for patients aged 65+ versus <65 years.