Comparing the outcome between multicentric and multifocal breast cancer: what is the impact on survival, and is there a role for guideline-adherent adjuvant therapy? A retrospective multicenter cohort study of 8,935 patients.

Multifocal (MF) and multicentric (MC) breast cancers have been comprehensively studied, and their outcomes have been compared with unifocal (UF) tumors. We attempted to answer the following questions: (1) Does MF/MC presentation influence the outcome concerning BC mortality?, (2) Is there an impact of guideline-adherent adjuvant treatment in these BC subtypes?, and (3)What is the influence of guideline violations concerning surgery (breast-conserving surgery versus mastectomy) on the survival of MF/MC BC patients? Between 1992 and 2008, we retrospectively analyzed 8,935 breast cancer patients from 17 participating breast cancer centers within the BRENDA study group. Of 8,935 breast cancer patients, 7,073 (79.2 %) had UF tumors, 1,398 (15.6 %) had MF tumors, and 464 (5.2 %) had MC tumors. RFS was significantly worse for MF/MC BC patients compared to patients with UF tumors (MF p = 0.007; MC p = 0.019). OAS was significantly worse for MC patients but not for MF patients compared to patients with UF tumors (MF p = 0.321; MC p = 0.001). Guideline adherence was significantly lower in patients with MF (n = 580; 41.5 %) and MC (n = 204; 44.0 %) compared to patients with UF (n = 3,871; 54.7 %) (p < 0.001) tumors. Guideline violations were associated with a highly significant deterioration in survival throughout all subgroups except for MC, with respect to RFS and OAS. For 100 %-guideline-adherent patients, we could not find any significant differences in RFS and OAS after adjusting by nodal status, grade, and tumor size. Furthermore, we could not find any significant differences in RFS and OAS in patients with MF or MC stratified by breast-conserving therapy (BCT lumpectomy and radiation therapy) and mastectomy. There is a strong association between improved RFS and OAS in patients with MF/MZ BC. There are no significant differences in RFS and OAS for patients with breast-conserving therapy or mastectomy.