AbstractPurposeBone marrow metastasis (BMM) is uncommon in breast cancer (BC), and early diagnosis is challenging. BMM lacks definitive treatment options and poses a great threat to the survival of patients. Herein, we investigated the clinical features, prognosis, and factors affecting the prognosis of BC patients with symptomatic BMM to help improve the understanding of this disease and provide effective diagnostic and treatment strategies.MethodsClinical data of 67 patients with BC and BMM were retrospectively analyzed for clinical characteristics, treatment, and prognosis of BMM. Univariate and multivariate analyses were performed to determine factors affecting overall survival following BMM (BMMOS).ResultsAmong patients with BMM, 86.6% were diagnosed after bone metastasis (BM), while 13.4% were diagnosed simultaneously with BM. A total of 73.1%, 13.4%, and 13.4% of the patients had hormone receptor‐positive/human epidermal growth factor 2‐negative (HR+/HER2−) tumors, HER2+ tumors, and triple‐negative tumors, respectively. The most common symptoms of BMM were the coexistence of anemia and thrombocytopenia (26.9%), anemia (19.4%), and pancytopenia (17.9%). The median BMMOS was 7.6 months (95% CI, 3.9–11.3). Univariate and multivariate analyses showed that BMMOS was associated with platelet count <75 × 109/L at the time of BMM diagnosis. The BMMOS of patients who underwent endocrine therapy, combined chemotherapy, and mono‐chemotherapy after BMM was 15.7, 9.7, and 8.6 months, respectively, whereas that of untreated patients was 2.9 months, and the difference among the results was statistically significant (χ2= 20.102,p< 0.0001). Changes in patient hemogram and/or body temperature during treatment were consistent with the overall effect of the disease (p< 0.0001).ConclusionBMM should be considered in BC patients with BM, an unexplained reduction in hemogram parameters, especially anemia and thrombocytopenia, and/or fever without chills. Active, effective, individualized treatment strategies can prolong BMMOS.