Abstract P3-05-14: Expression of the tumor associated carbohydrate antigen Tn and immune effectors in invasive breast cancer

Abstract

Abstract Background: Glycosylation is a post-translational modification generating complex carbohydrate O-glycans. Tn antigen, a N-acetyl-galactosamine-α-O-Ser/Thr residue that is the core glycosylated component of complex mucin-type O-glycans, is expressed in breast cancers. Tn has been associated with invasion, survival and decreased T-cell mediated immune response in several types of cancer including breast cancer. There is therefore a potential rationale to combine Tn vaccine with checkpoint blockers such as PD-1/PDL-1 inhibitors. Little is known regarding the link between the respective expression of Tn antigen, PDL-1, and TILs, in breast cancer. Our study aimed at characterizing Tn expression in a series of invasive breast cancers, and its correlation with immune response. Methods Tn expression was analyzed by immunohistochemistry performed on a tissue microarray of 1864 invasive breast cancer samples (1850 patients for statistical analyses), consisting of 189 (10%) TNBC, 1601 (86%) ER and/or PR positive à checker tumors and 191 (10%) HER-2 positive tumors treated at our institution between 2005 and 2013. Among these cases, 50 luminal B tumors and 50 TNBC were selected for full section and immune analysis, i.e. to study the pattern of Tn expression across whole tumor section and the link between Tn expression and the level of CD3+ and CD8+ infiltrates, and PDL-1 expression. The level of Tn expression was assessed using H-score, combining the percentage of stained cells with staining intensity. Results: In the 100 initial samples, Tn expression was observed in 95%, with a H-Score>10 in 85% of the cases, and with homogeneous staining across the whole tumor section in 86% of the cases. Tn expression was increased in Luminal B subtype as compared to TNBC, with a mean H-Score of 100.9 vs 55, respectively (p <0,0001). The CD3+ infiltrate was more important in TNBC as compared to luminal B tumors (mean stromal CD3+: 34.3% vs 21.2%, p=0,0052). No significant difference was found for the CD8+ infiltrate. PDL-1 expression in stromal cells (≥1%) was observed in 43% of the cases, and increased in TBNC as compared to Luminal B (mean of 7.3% vs 2.2% of cells respectively, p=0.0252). In both tumor subtypes, we observed a positive correlation between the CD3/CD8 infiltrates and PDL-1 expression in stroma cells (p<0,0001), but not with Tn expression. In the TMA cohort, Tn expression was observed in 1723 (92%) tumors with a mean H-Score of 82.75. Similarly, to the results obtained in full section, Tn expression was less intense in TNBC as compared to other subtypes (mean H-Score of 62 vs 85, p<0.001). Tn expression was lower in histological grade I as compared to grade II/III tumors (64,69 for grade I, 88,84 for grade II and 88.99 for grade III, p<0.0001), and significantly higher in HER2 positive tumors versus others (mean H score 62,06 for HER2-/RE-, 119,05 for HER2+ and 80,25 for HER2-/RE+, p<0.0001). Conclusion: Our study shows a lower level of expression of Tn antigen in TNBC as compared to luminal tumors. We could not identify any correlation between Tn antigen expression and immune status of the tumor as defined by CD3+, CD8+ and PDL-1+ infiltrate in tumor stroma. The role of Tn antigen in the HER2-positive subgroup requires further investigation. Citation Format: Verret B, Rossoni C, Lebeherec D, Michiels S, Castanon-Alvarez E, Leclerc C, Delaloge S, Artaud C, Lacroix-Tikri M. Expression of the tumor associated carbohydrate antigen Tn and immune effectors in invasive breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-05-14.