Patient factors and modifications to intended chemotherapy for women with Stages I–<scp>IIIA</scp> breast cancer

Modifications to intended chemotherapy regimens may be due to various reasons and may impact patient outcomes. Understanding which factors are associated with chemotherapy modifications can help inform treatment planning and improve cancer care. We examined the association between patient/tumor factors and modifications to intended chemotherapy in women with Stages I-IIIA breast cancer who were treated at Kaiser Permanente Northern California and Kaiser Permanente Washington from 2005 to 2019. Modifications were defined as any dose reductions in the first cycle or throughout chemotherapy, regimen change, treatment delay (single delay >14 days) or receiving fewer cycles of any drugs than expected. We used generalized linear models of the Poisson family with a log-link function to calculate prevalence ratios (PRatios). Of 9700 women receiving adjuvant chemotherapy, 34.6% had chemotherapy modifications. Selected results are shown: positive associations were observed with age (PRatio_{80+ vs. 18-39}: 1.93; 95% confidence interval [CI]: 1.50-2.50; p-trend <.001), body mass index (BMI) (PRatio_{≥35 vs. 18.5 to <25}: 1.53; 95% CI: 1.41-1.65; p-trend <.001), and Charlson comorbidity index (PRatio_{3+ vs. 0}: 1.33; 95% CI: 1.19-1.48; p-trend <.001), while more recent years of diagnosis were associated with decreased prevalence of treatment modifications (PRatio_{2015-2019 vs. 2005-2009}: 0.65; 95% CI: 0.61-0.69; p-trend <.001). Stage was also positively associated (PRatio_{Stage IIIA vs. I}: 1.24; 95% CI: 1.13-1.35; p-trend <.001), as was human epidermal growth factor-2 positive status (PRatio: 1.99; 95% CI: 1.89-2.10). In conclusion, patients with the highest likelihood of chemotherapy modifications represent those who may have more complex prescribing needs, including those of older age, higher BMI, and more comorbidity. Further understanding of how modifications could impact outcomes within these groups can inform and improve cancer care.