Leukocyte nadir as a predictive factor for efficacy of adjuvant chemotherapy in breast cancer. Results from the prospective trial SBG 2000–1

<b>Background:</b> Retrospective studies have suggested that chemotherapy-induced leukopenia is associated with improved recurrence-free or overall survival. The SBG 2000–1 trial was designed to verify the favorable prognosis associated with chemotherapy-induced leukopenia in early breast cancer. Patients not experiencing chemotherapy-induced leukopenia were randomized into standard dosed or individually escalated chemotherapy doses based on the grade of leukopenia after a first standard dose. <b>Patients and methods:</b> 1452 women in Sweden and Denmark with operable node-positive or high-risk node-negative breast cancer aged 18–60 years were recruited to participate in this trial. Participants received a first FEC cycle at standard doses (600/60/600 mg/m²). Patients (<i>n</i> = 1052) with nadir leukopenia grade 0–2 after the first cycle were randomized between either 6 standard FEC or 6 tailored FEC courses with doses of epirubicin and cyclophosphamide escalated during courses 2 and 3 and thereafter aimed at achieving grade 3 leukopenia. Patients with nadir leukopenia grade 3–4 after the first course continued treatment with standard FEC. Results of the randomized comparison has been published previously. The present study focuses on chemotherapy-induced leukopenia as a covariable with outcome in randomized and non-randomized patients. The prognostic value of leukopenia after course 3, was studied in a Cox model adjusted for cumulative doses of epirubicin and cyclophosphamide. The association of chemotherapy-induced leukopenia with prognosis was a preplanned secondary endpoint for this trial. <b>Results:</b> The eight-year distant disease-free survival was 73%, 77%, 78% and 83% for patients with leucocyte nadir grade 0, 1, 2 and 3–4, respectively. Higher degree of leukopenia was highly significantly associated to improved distant disease-free survival (HR 0.84, 95% CI 0.74–0.96, <i>p</i> = .008) and overall survival (HR 0.87 (0.76–0.99, <i>p</i> = .032). <b>Conclusion:</b> This prospective study confirms that chemotherapy-induced leukopenia is a covariable with outcome in primary breast cancer, even after adjustment for chemotherapy doses.