Clinicopathological characteristics and survival outcomes in spindle cell carcinoma (SpCC) of the breast: A SEER population-based study

Spindle cell carcinoma (SpCC) of the breast is a rare entity. The aim of this study was to provide more information for understanding this disease and to improve the management of it in the clinic. Patients with SpCC and invasive ductal carcinoma (IDC) of the breast were identified through the surveillance, epidemiology, and end results (SEER) database (2001-2018). 227 patients with SpCC and 565,388 patients with breast IDC were enrolled in the present cohort study. Comparative analyses were performed to investigate the heterogeneity in the clinicopathological characteristics and survival outcomes between these 2 groups. Propensity score matching (PSM) was used to balance the influences of baseline clinicopathological differences. The multivariate Cox proportional hazard model was carried out to identify potential prognostic factors of SpCC. Compared with IDC, patients with SpCC had a higher proportion of older patients and white individuals, a higher tumor grade, a lower tumor stage, a larger tumor size, a higher incidence of distant metastasis, a lower rate of lymph node involvement, a higher proportion of triple-negative breast cancer (TNBC) and less access to therapeutics. The prognosis of SpCC was profoundly poorer than that of IDC, whether before or after PSM. Subgroup analysis further showed that SpCC-TNBC had a worse clinical outcome than IDC-TNBC. Finally, we found that older age, advanced T stage, N stage and M stage were all risk factors for SpCC. SpCC of the breast presented with increasing aggressive behavior in comparison with IDC and inferior clinical outcome than IDC for both the whole group and the TNBC subgroup. Distinguishing SpCC from IDC is critical for improving treatment efficacy; therefore, further research must focus on this rare but aggressive disease.