Clinicopathological characteristics and treatment outcomes of luminal B1 breast cancer in Taiwan

BACKGROUND Hormone receptor-positive, human epidermal growth factor receptor II (HER2)-negative luminal B1 breast cancer is associated with a higher risk of disease relapse than luminal A breast cancer. Therefore, we assessed and compared the distant metastasis pattern and clinical outcomes associated with luminal B1 and luminal A breast cancer in an Asian population. METHODS In this observational study, we assessed patients with estrogen receptor-positive, HER2-negative breast cancer who underwent surgery from 2009 to 2016. Patients were classified into luminal A or luminal B1 subsets via immunohistochemical analysis. Disease-free survival, post-metastasis survival, and overall survival were estimated; time to disease relapse and patterns of distant metastasis were compared. Risk of relapse and mortality were assessed using Cox proportional hazards model. RESULTS Patients with luminal B1 breast cancer (n = 677) were significantly younger and had larger tumors and a higher degree of affected axillary lymph nodes, lymphovascular invasion, and tumor necrosis than those with luminal A breast cancer (n = 630). Higher rates of local recurrence and distant metastasis were observed for luminal B1 (both p < 0.05); however, no difference was observed in the specific distant metastatic sites. We observed a significant increase in disease relapse risk in luminal B1 patients compared with that in luminal A (hazard ratio: 2.157, 95% confidence interval: 1.340-3.473, p < 0.05). Patient age, tumor size, stage, lymphovascular invasion, and receiving chemotherapy and hormone therapy were independent risk factors for metastasis and recurrence. Only the luminal B1 subtype (hazard ratio: 5.653, 95% confidence interval: 1.166-27.409, p < 0.05) and stage (hazard ratio: 3.400, 95% confidence interval: 1.512-7.649, p < 0.05) were identified as independent risk factors for post metastatic mortality. CONCLUSION Luminal B1 breast cancer has aggressive tumor biology compared with luminal A breast cancer in the follow-up period. However, there was no significant difference in the disease relapse pattern between the groups.