Average duration of prior treatment lines predicts clinical benefit to eribulin chemotherapy in patients with metastatic breast cancer

Purpose The aim of this study was to identify factors associated with progression-free survival (PFS) and overall survival (OS) in patients with metastatic breast cancer (MBC) treated with eribulin in a real-world setting, to improve information provision in those considering treatment. Methods Patients treated with eribulin for MBC at The Christie NHS Foundation Trust, Manchester, UK, between August 2011 and December 2018 were included (n = 439). Data were collected by retrospective review of medical records and electronic prescribing systems. Factors such as biological subtype, distant recurrence-free interval, previous lines of chemotherapy and the 'average duration of previous treatment lines' (ADPT) (calculated as: (date of initiation of eribulin-date of MBC) / the number of previous treatment lines in the metastatic setting) were evaluated for prognostic impact using Cox proportional hazards regression. Results In the full cohort, the median PFS and OS were 4.1 months (95% CI 3.7-4.4) and 8.6 months (95% CI 7.4-9.8), respectively. Outcomes were significantly inferior for those with triple-negative breast cancer (TNBC) (n = 92); PFSTNBC: 2.4 months (95% CI 2.1-3.0), p = < 0.001 and OSTNBC: 5.4 months (95% CI 4.6-6.6), p = < 0.001. ADPT was the only factor other than subtype significantly associated with PFS and OS. Longer ADPT was also significantly associated with PFS and OS in those with TNBC. For example, women in the lowest ADPT tertile (< 5.0 months) achieved a median OS of only 4.3 months, whereas those in the upper ADPT tertile (> 8.7 months) had a median OS of 12.1 months (p = 0.004). Conclusion Our results indicate that the ADPT lines is an important factor when predicting the outcome with eribulin chemotherapy in a palliative setting and that quantitative guidance on the likely PFS and OS with treatment can be provided using ADPT. Validation in additional cohorts is warranted.