Abstract PO5-02-07: Multifocal breast cancer: tumor biology and prognostic importance
Authors: Söderberg Emma , Sund Malin , Wärnberg Fredrik , Garmo Hans , Wennstig Anna-Karin , Holmberg Lars , Nilsson Greger , Wadsten Charlotta 
Published: May 2024

Abstract
&gt;Multifocal breast cancer: tumor biology and prognostic importance Background The incidence of multifocal breast cancer (MBC) varies widely in the literature and recent reports indicate that the incidence of MBC is increasing. Several studies have shown similar tumor biology in the different foci of multifocal tumors, and it has been suggested that multifocal tumors may in fact be intramammary metastases and thus be a sign of a more aggressive cancer type than unifocal tumors. Knowledge regarding outcome and optimal treatment of MBC compared to unifocal breast cancer (UBC) is still limited. The aim of the present study was to explore if multifocal breast cancers have less favorable characteristics and prognosis compared to unifocal breast cancers. Method Patient and tumor characteristics were obtained from Breast Cancer database Sweden (BcBaSe3) including women with invasive breast cancer 2008-2019 who had undergone primary surgery. Women with distant metastases at time of diagnosis, women receiving neoadjuvant systemic therapy, and men were excluded. Overall- and breast cancer specific survival were calculated with Kaplan-Meier and Cox-regression analyses. Results A total of 71607 women met our inclusion criteria, 11961 (16.7%) with MBC and 59512 (83.3%) with UBC. Among women with MBC, 64.1% underwent mastectomy compared to 32.4% of women with UBC and 40.1% with MBC underwent complete axillary lymph node dissection compared to 23.5% of the women with UBC. MBC was associated with higher T-stage (T2 31.9% vs. 25.8% and T3 4.6% vs. 2.6%. p&lt; 0.001) and higher N-stage (N+ 13.7% vs. 8.4%, P&lt; 0.001), compared to UBC. MBC were more often of lobular type (18.8% vs. 12.4%, P&lt; 0.001), of higher grade (grade 3 29.3% vs. 27.3%, p&lt; 0.001), with positive hormone receptor status (88.4% vs. 86.7%, p&lt; 0.001), and Her2 positivity (13.3% vs. 10.9%, p&lt; 0.001). Adjuvant systemic treatment was more frequently administered to women with MBC, adjuvant chemotherapy (45.3% vs. 33.3%, p&lt; 0.001) and endocrine treatment (82.9% vs. 75.3%, p&lt; 0.001). Breast cancer specific 10- year survival was 86.4% and 88.5% for MBC and UBC respectively, hazard ratio for breast cancer death 1.19 (95 % confidence interval, 1.11- 1.28). Overall survival did not differ between the two groups (10-year survival 76.0%, p=0.35) Conclusion MBC appears to have a more aggressive tumor biology than UBC, with the exception of hormone receptor status and MBC is associated with decreased breast cancer specific survival. Further analysis of possible interactions with different treatment methods will be conducted.
Citation Format: Emma Söderberg, Malin Sund, Fredrik Wärnberg, Hans Garmo, Anna-Karin Wennstig, Lars Holmberg, Greger Nilsson, Charlotta Wadsten. Multifocal breast cancer: tumor biology and prognostic importance [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-02-07.