Upfront Taxane Could Be Superior to Pegylated Liposomal Doxorubicin (PLD): A Retrospective Real-World Analysis of Treatment Sequence Taxane-PLD versus PLD-Taxane in Patients with Metastatic Breast Cancer

Patients with breast cancer, that has spread and does not respond to hormone treatment, are usually treated with chemotherapy. If one kind of chemotherapy fails, another kind is started. There are various options and different chemotherapies to choose, but currently there is no standard, which kind to use first. Our aim was to find out, whether starting with one chemotherapy is better than with the other. We have investigated all patients with metastatic breast cancer who have been treated with the two most frequently used kinds of chemotherapy ("taxanes" and "PLD") at the University Hospital Basel, Switzerland. We found that patients who have received taxanes first survived longer than patients who received PLD first. These results are astonishing and highly relevant to patients with breast cancer and their treating physicians. Because our study was backward-looking, we cannot rule out that our results are confounded by any unknown factors other than the kind of chemotherapy. This important question should be investigated in a prospective clinical trial. Background: Patients with endocrine-resistant metastatic breast cancer (MBC) require cytostatic therapy. Single-agent taxanes and anthracyclines, including pegylated liposomal doxorubicin (PLD), are standard treatment options. There are no prospective data regarding optimal treatment sequences, and real-world data regarding both treatment options are limited. Methods: We analyzed electronic records of all patients with Her2-negative MBC treated with either first-line PLD or first-line taxane and subsequent crossover at the University Hospital Basel between 2003 and 2021. The primary endpoint was time to next chemotherapy or death (TTNC). Secondary endpoints were overall survival (OS), progression-free survival (PFS), and objective response rate (ORR). We used the Kaplan-Meyer method and logrank test to compare time-to-event endpoints and the Fisher exact test to compare discrete variables. Results: We retrospectively identified 42 patients with Her2-negative MBC who have received either single-agent PLD or single-agent taxane as first-line chemotherapy with subsequent crossover, including 23 patients who received first-line PLD and 19 patients who received first-line taxane. Baseline characteristics were similar between treatment groups. Treatment sequence PLD-taxane was significantly inferior to taxane-PLD regarding all endpoints: median TTNC 4.9 vs. 9.9 months (p = 0.006), median OS 17.8 vs. 24.6 months (p = 0.05), median PFS 4.4 vs. 9.0 months (p = 0.005), and ORR 13% vs. 53% (p = 0.01). Conclusions: Here, we report a first retrospective head-to-head comparison of the treatment sequence PLD-taxane versus taxane-PLD in patients with MBC, showing a substantial advantage of using taxanes first, followed by PLD. An inherent treatment bias in favor of first-line taxanes cannot be excluded, thus calling for prospective validation.