Abstract P3-06-27: BRCAness is important to identify TNBC subtype resistant to taxanes

Abstract

Abstract BACKGROUND: Triple negative breast cancer (TNBC) is heterogeneous and consists of tumors associated with basal like, BRCA related and cancer stem cell (CSC) phenotypes. Although anti-cancer agents are substantial for treating TNBC, existing ones do not work in some subpopulation in TNBC at all. However, it has not been reported that subdivision of TNBC is useful for choosing ant-cancer agents. AIM: To examine whether subdividing TNBC is beneficial for tailored chemotherapy and to identify predictive factors for existing anti-cancer agents in TNBC. METHODS: Sixty-six TNBC cases from a randomized phase II trial comparing TCx6 (TC6) with FEC followed by docetaxel (FEC-D) as neoadjuvant chemotherapy for hormone receptor-negative breast cancer (Kanagawa Breast Oncology Group 1101 Study). TNBC was subdivided by 1) IHC of CK 5/6 and EGFR into basal- and non-basal subtypes, and 2) MLPA of BRCA1 into BRCA1 and non-BRCA1 subtypes. The pCR rates were examined according to each regimen and subtype. 3) The association of grade 3 pCR was examined with Ki-67, p53, aldehyde dehydrogenase (ALDH) 1 and topoisomerase 2A (topoIIα) by IHC and TOP2A by FISH for each regimen. RESULTS: 1) In basal subtype, the pCR rate was significantly higher for FEC-D (42.9%) compared with TC6 (13.6%) (p=0.033), but it was equivalent in non-basal subtype (FEC-D vs TC: 25.0% vs 36.4%, p=0.554). 2) In BRCA1 subtype, it was more significant (FEC-D vs TC: 53.8 % vs 13.3%, p=0.022). 3) An association between pCR and low ALDH1 expression was found in both FEC-D and TC6 (OR: 3.75 and 2.73). High topo IIα protein expression was associated with pCR in FEC-D (OR: 3.5). DISCUSSION: TC6 was less effective than FEC-D in basal subtype and BRCA1 subtype, showing that taxanes cannot exert their anticancer role in tumors with BRCA1 dysfunction. Although basal subtype may contain more BRCA1-defective tumors than non-basal subtype, MLPA of BRCA1 was better to identify subtype resistant to taxanes than CK5/6 and EGFR. ALDH1 predicted treatment efficacy, and could therefore represent a marker of resistance to conventional chemotherapy. Citation Format: Takashi Ishikawa, Kazutaka Narui, Kazuhiro Shimada, Kumiko Kida, Mari S Oba, Mikiko Tanabe, Yasushi Ichikawa, Sadatoshi Sugae, Itaru Endo. BRCAness is important to identify TNBC subtype resistant to taxanes [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-06-27.