Abstract P1-07-03: Mesenchymal subtype negatively associates with the presence of immune infiltrates within a triple negative breast cancer classifier
Authors: Grigoriadis A , Quist J , Mirza H , Cheang MC , Ring BZ , Hout DR , Bailey DB , Seitz RS , Tutt AN 
Published: March 2017

Introduction: Lehmann and colleagues (Lehmann et al., 2011) devised a gene expression classification system for triple negative breast cancer (TNBC) consisting of seven subtypes—IM, BL1, BL2, LAR, M, MSL, and UNS (unselected). We (Ring et al., 2016) recently modified this original algorithm of 2188 gene subtyping into a 101-gene algorithm. In addition to a reduction of genes, the 101-gene algorithm has two methodological differences: first, the immunomodulatory (IM) signature was treated not as a subtype but rather as a binary feature of one of the other subtypes (e.g. BL1/IM+, LAR/IM-); second, when tumors—by a predefined correlation coefficient—showed traits of more than one subtype, both subtypes were reported as “dual subtypes.”

Aim: Our aim was to apply the 101-gene algorithm for TNBC subtyping and to establish the relation of TNBC subtypes with their IM-status across several independent data sets.

Methods: 951 patients from four independent TNBC cohorts with available gene expression data were analyzed by the 101-gene algorithm. Of these 848 were classified with at least one subtype.

Results: The distribution of the 5 TNBC subtypes in both single and dual subtypes was 47%,10%,15%,18%,11%, for BL1, BL2, LAR, M, and MSL respectively. The majority of cases gave only one subtype (572, 67%) with M (Mesenchymal) being 9% (n=54) of these. Given this frequency of 9% of M as a baseline, in the remaining 276 (33%) cases with dual subtypes, the expectation that M would be one of the two is 11% (64 subtype calls). However, M is one of the two of the dual subtypes at a much higher frequency of 40% (222 subtype calls, Chi-Squared, P&lt;0.0001). IM+ is a common feature across these cohorts (n=310 or 37%). When examining the IM feature within the patients exhibiting the M subtype as either a single subtype or one of the two dual subtypes (n=276, 33%), IM positive tumors are never of the M phenotype (Chi-Squared, p&lt;0.0001).

Conclusions: We further have confirmed with the 101-gene algorithm that the IM signature inversely associates with the M subtype as it has been observed with the 2188 gene algorithm (Lehmann et al., 2016). Moreover, the M signature is occasionally a confounder of other subtypes however still identifies those tumors negative for immune infiltrates. This raises important opportunities to understand the relationships between intrinsic tumor biology reflected in TNBC subtypes and their interaction with variable immune cell stroma which are the subject of ongoing analyses.

Citation Format: Grigoriadis A, Quist J, Mirza H, Cheang MC, Ring BZ, Hout DR, Bailey DB, Seitz RS, Tutt AN. Mesenchymal subtype negatively associates with the presence of immune infiltrates within a triple negative breast cancer classifier [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-07-03.