Abstract P4-04-04: Triple-negative (TN) and HER2+ breast cancers (BC) have different immune milieu in primary and metastatic tumors
Authors: Bianchini G , Riba M , Zambelli S , Safonov A , Ogiya R , Jiang T , Hatzis C , Niikura N , Zambetti M , Iwamoto T , Pusztai L , Gianni L 
Published: May 2016

Background: In TN and HER2+ early BCs, a high immune infiltration is linked to good prognosis and improved treatment benefit. Little is known about the characteristics of the immune milieu of BCs in metastatic disease. We aimed to investigate differences of the immune microenvironment between cohorts of primary early breast cancer (EBC) and metastatic (MBC) tumors according to molecular subtypes.

Methods: We identified publicly available gene expression profiles (GEPs) of MBCs profiled either on Agilent (n=12, cohort I) or AffymetrixU133A (n=36, cohort II). These included 21 ER-/HER2- (TN), 10 HER2+ and 17 ER+/HER2- (Luminal). From GEPs of EBC profiled on the same platforms, we randomly selected two cohorts with the same molecular subtype composition (n=65 and n=230) and compared them with MBCs. We assessed differential expression of 40 pre-selected immune genes belonging to six immune-related metagenes [CD8, IGG and MHC2, related to T cells, plasma cells and antigen presenting cells respectively; MHC1, STAT1 and IF.I related to HLA class I genes; and genes modulated by interferon (Gianni L SABCS 2012)]. We also evaluated β2-microglobulin (B2M), for its role in the MHC1 complex, and an immune signature associated with benefit from pembrolizumab in melanoma (Ribas A ASCO 2015).

Results: In cohort I (Agilent), only 33 genes were annotated. Overall, 16/33 (48.4%) genes had a significantly lower expression in MBC (p&lt;0.05). In TN and HER2+ MBCs 18 and 11 genes were significantly lower than in EBC, respectively (p&lt;0.05) (6 in both), while only one was lower in luminal MBCs (IGHM). In cohort II (Affymetrix), 26/40 genes (65%) had lower expression in MBC (p&lt;0.05). Considering molecular subtypes, 25 and 19 genes were lower in TN and HER2+, respectively (17 in both), and only one in ER+/HER2- (IL7R). In ER+/HER2- one gene was higher in MBC (IFIT2). In TN and HER2+ the genes with lower expression in MBC belong to all immune functional categories, in particular MHC1 (HLA-A, B and C), STAT1 (STAT1, CXCL10, CXCL11, GBP1), MHC2 (HLA-DQB1 and DRB4) and T cells (CD52, IL7R and TRBC1). B2M was significantly lower in all MBC patients, and in HER2+ and TN groups both in cohort I (p=0.0002; p=0.006 and p=0.0005, respectively) and in cohort II (p&lt;1E10-6; p=0.0008 and p=0.00004, respectively), while it was modestly lower in ER+/HER2- in cohort II only (p=0.027). The signature associated with benefit from pembrolizumab in melanoma was significantly lower in TN and HER2+ MBC in both cohort I (p=0.003) and cohort II (p=0.001), but not in luminal cases.

Conclusions: TN and HER2+ MBCs have a "colder" immune microenvironment than primary tumors, with significantly lower expression of genes related to immune response and to antigen presentation (B2M and MHC1). This is consistent with the lower TILs we have described in a small series of paired EBC-MBC (Ogiya R ASCO 2015), suggesting the engagement of mechanisms of immune escape during the metastatic process. However, the "cold" immune milieu observed in MBC could also result from selection of low immunogenic tumors more likely to relapse. Our findings suggest that use of immune-checkpoints inhibitors in MBCs may require the combination with agents able to turn on an immunogenic response.

Citation Format: Bianchini G, Riba M, Zambelli S, Safonov A, Ogiya R, Jiang T, Hatzis C, Niikura N, Zambetti M, Iwamoto T, Pusztai L, Gianni L. Triple-negative (TN) and HER2+ breast cancers (BC) have different immune milieu in primary and metastatic tumors. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-04-04.