4CPS-284 Treatment of cyclin inhibitor induced neutropenia: impact on progression free survival

Background and importance The incidence of neutropenia in cyclin inhibitor (CI) treatment of luminal metastatic breast cancer (LMBC) is very high and leads to a reduction or delay in the required dose. Aim and objectives To analyse the efficacy of granulocyte colony stimulating factor (G-CSF) in CI treatment. We used filgrastim as G-CSF. Material and methods A retrospective study of patients that initiated CI treatment between March 2018 and April 2020 was conducted. Results The cohort included 69 LMBC patients treated with CI. Median age was 65 years (41–89), 20 (29%) patients had a metastatic debut, 21 (30%) progressed during endocrine adjuvant treatment and 28 (41%) had progressed after 5 years of hormonal treatment. 44 patients (63%) received CI treatment as firstline treatment, 10 (15%) after progression to firstline with hormonotherapy and 15 (22%) after progression to chemotherapy. The visceral disease was present in 41%. 48 patients received adjuvant systemic treatment, of whom 35 received adjuvant chemotherapy. 58 patients presented with neutropenia (ANC Global median progression free survival (PFS) was 10.88 months (95% CI 5.8 to 15.9) with 38 events. Patients treated as firstline had a PFS of 14 months compared with 8 months for secondline (log rank 0,134). Patients with neutropenia had a superior PFS (15 vs 8 months; log rank p=0.006); 16 versus 9 months for firstline and 13 versus 5 months for secondline. We did not find any correlation between G-CSF use and clinical variables, such as firstline or secondline, visceral metastasis, or diagnosis and metastatic interval. PFS in patients with or without filgrastim was similar (14 vs 12 months). Conclusion and relevance CI induced neutropenia is a widespread complication and correlated with PFS in our patient cohort: 15 versus 8 months in the whole group. G-CSF treatment did not affect PFS but can help to maintain treatment and avoid early relapses. Whether neutropenia induced by treatment with CI behaves as a prognostic factor and whether the use of G-CSF could provide clinical benefit should be studied. References and/or acknowledgements Conflict of interest No conflict of interest