Background and Aims: Triple-negative breast cancer (TNBC) is a subtype of breast cancer with poor prognosis. Due to the lack of endocrine therapy and anti-HER-2 therapy targets, adjuvant chemotherapy is its main treatment strategy. As one of the most common side effects of chemotherapy, bone marrow suppression has an unclear effect on the prognosis of TNBC. This study was conducted to investigate the effect of the degree of bone marrow suppression on the prognosis of TNBC after adjuvant chemotherapy. 
Methods: According to the inclusion and exclusion criteria, the clinical, pathological and follow-up data of patients with TNBC who underwent adjuvant chemotherapy with epirubicin and cyclophosphamide followed by docetaxel (EC-T) regimen in the Department of Breast of the Third Affiliated Hospital of Zhengzhou University from January 2012 to December 2017 collected for a retrospective analysis. Based on the WHO classification criteria for acute and subacute toxicity of anticancer drugs, the enrolled patients were divided into mild group (degree 0–II) and severe group (degree III–IV) according to the degree of bone marrow suppression after chemotherapy. The clinicopathologic features, disease-free survival (DFS), local-regional recurrence-free survival (LRFS), distant recurrence-free survival (DRFS) and total survival (OS) were compared between the two groups of patients.
Results: A total of 168 patients were included with 102 cases in mild group and 66 cases in severe group. There were no statistical differences in the baseline clinicopathologic characteristics between the two groups of patients (all P>0.05). The median follow-up time for mild group was 66.5 (22-95) months, and for severe group was 67.5 (28-96) months. There were 38 and 15 DFS events in mild group and severe group respectively, and the median DFS in mild group was 84 months, while severe group did not reach a median DFS; 20 and 8 OS events occurred in mild group and severe group respectively, and neither group achieved a median OS; 17 and 8 LRFS events were recorded in mild group and severe group respectively, and neither group reached a median LRFS; there were 27 and 10 DRFS events in mild group and severe group respectively, and neither group reached a median DRFS. Survival analysis showed that the 5-year DFS rate of severe group was higher than that of mild group (78.3% vs. 69.2%, HR=0.45, P=0.037); there was no significant difference in the 5-year OS rate between severe group and mild group (91.1% vs. 83.3%, HR=0.602, P=0.183; no statistical difference in the 5-year LRFS rate between severe group and mild group (89.1% vs. 83.3%, HR=0.625, P=0.270); the 5-year DRFS rate of severe group was higher than that of mild group (85.5% vs. 77.0%, HR=0.41, P=0.048).
Conclusion: TNBC patients with grade III–IV myelosuppression during adjuvant chemotherapy with EC-T regimen have a better prognosis than those with grade 0–II myelosuppression, suggesting that chemotherapy-induced hematological toxicity can be regarded as a sign of the effectiveness of chemotherapy, and is helpful for prognosis estimation and treatment decision making. For patients with only mild bone marrow suppression, following more intense treatment may be required. The issue that needs attention is that severe myelosuppression will increase the risk of neutropenic fever and infection, so the pros and cons must be weighed, and strict monitoring as well as symptomatic treatment must be offered.