IntroductionMetronomic chemotherapy (MCT) is increasingly used in oncology due to its favorable therapeutic index. There is still a lack of evidence for MCT in metastatic breast cancer (MBC). In this retrospective unicenter study, we demonstrated real-word data on MCT in MBC.MethodsMBC patients who received metronomic oral cyclophosphamide (CTX) (50 mg daily) and methotrexate (MTX) (2.5 mg every other day), CTX and capecitabine (CAPE) (500 mg thrice daily), CTX, or vinorelbine (VRL) (30 mg daily) alone for at least 4 weeks between 2009 and 2021 were included. The primary endpoint was disease control rate (DCR) ≥24 weeks. Secondary endpoints were progression-free survival (PFS) and overall survival (OS). Patient characteristics and therapy response were analyzed using χ2test. For survival analyses, Kaplan-Meier estimator and log-rank test were used.ResultsSeventy-two patients were identified. Sixty-two patients received CTX/MTX, three CTX/CAPE, two CTX, and five VRL. Median age at diagnosis MBC and at start of MCT was 59.0 years and 64.5 years, respectively. 72.2% tumors were hormone receptor positive and 27.8% were triple-negative. 54.2% patients had more than two different metastases. 80.6% patients showed visceral involvement. 31.9% patients achieved DCR ≥24 weeks. Median PFS was 17.0 weeks (95% CI 14.5–19.5) and median OS was 58.0 weeks (95% CI 29.0–87.0). MCT showed similar DCR ≥24 weeks and clinically meaningful but not statistically significant shorter median PFS compared to prior therapy (31.9% versus 32.8% [p= 0.570] and 17.0 weeks versus 20.0 weeks [p= 0.093], respectively) and statistically significant higher DCR ≥24 weeks and longer median PFS compared to subsequent therapy (31.9% versus 17.4% [p= 0.038] and 17.0 weeks versus 12.0 weeks [p= 0.006], respectively). Three (4.2%) patients terminated MCT because of toxicity.ConclusionIn this real-world retrospective study, MCT was effective and well tolerated and may thus represent a valuable treatment option in selected MBC patients.