Abstract P2-07-03: Correlation of immune-related protein expression with hormone receptor (HR) status and pathologic response to neoadjuvant paclitaxel/trastuzumab/pertuzumab (THP) among patients with early-stage HER2+ breast cancer
Authors: Waks Adrienne G. , Huang Ying , Hether Tyler , Ogayo Esther R , Kadel Sapana , Alberti Jillian , Tolaney Sara M , Krop Ian E , Divakar Prajan , Metzger Otto , O'Donnell Madison L , Church Sarah , Winer Eric P , Guerriero Jennifer L. , Mittendorf Elizabeth A 
Published: March 2022

Background: Immunological differences between HER2+ breast tumors that are HR+ versus HR- have not been widely explored. DAPHNe was a single-arm prospective clinical trial enrolling patients with clinical anatomic stage II-III HER2+ breast cancer to neoadjuvant treatment with THP. Here, we examine differential expression of immune-related proteins between HR+/HER2+ and HR-/HER2+ tumors in pre-treatment biopsies from trial participants, and analyze correlates of pathologic response to THP, overall and by HR status. Methods: A baseline research biopsy was required in all participants prior to initiation of neoadjuvant therapy. All patients received 12 weeks of neoadjuvant THP; 5 patients also received neoadjuvant AC given incomplete clinical response to THP, and are excluded from residual cancer burden (RCB) analyses. The trial primary endpoint, feasibility of de-escalation to antibody doublet therapy only (HP) following pCR, was previously reported. Protein expression profiling of baseline research biopsies was performed on the NanoString GeoMx® platform using a 58-protein immune cell profiling panel. Regions of interest (ROI; up to 12 per slide) were identified by a pathologist based on tumor cell, immune cell, and/or T cell presence, and all ROI were segmented into tumor vs stroma. Protein data quality controls were normalized by isotypes. Linear mixed effect models were used for differential expression comparisons; p-values were estimated using Satterthwaite’s method. Results: 97 pre-treatment breast tumor specimens were analyzed: 64 patients had HR+ tumors, 32 HR-, 1 unknown; 67 patients had favorable (RCB 0/1) response to preop therapy, 30 patients had unfavorable response (RCB 2/3). Multiple significant differences were observed between protein expression in HR+ versus HR- tumors (Table 1). Multiple immune cell types, as well as checkpoint proteins PD-L1 and IDO1, were higher in HR- patients, whereas checkpoint proteins B7-H3 and TIM3 were higher in HR+ patients. In the overall population, higher HER2 and PD-L1 expression were significant predictors of favorable RCB response, while higher ER alpha and Bcl-2 expression were significant predictors of unfavorable RCB response (Table 2). Conclusions: As anticipated, the strength of HER2 expression and ER expression were the most significant predictors of favorable and unfavorable RCB response to neoadjuvant THP, respectively. This highly multiplexed protein expression analysis demonstrated significant differences between the immune microenvironment of HR+ and HR- HER2+ breast tumors, implying that distinct immunological targets should be explored in the treatment of HER2+ breast cancer according to HR status.

Table 1.Differences between HR+/HER2+ and HR-/HER2+ patientsStroma compartmentTumor compartmentHigher in HR+ER alpha* (fold-change 2.25)ER alpha* (8.94)Fibronectin (1.68)Bcl-2* (1.98)B7-H3 (1.44)Fibronectin* (1.90)PR (1.69)TIM-3 (1.37)Higher in HR-CD27* (fold-change 1.36)IDO1 (1.50)IDO1 (1.77)S100B (1.44)CD45 (1.45)MART1 (1.33)CD3 (1.35)CD20 (1.34)STING (1.33)CD4 (1.30)ICOS (1.30)CD45RO (1.28)CD40 (1.28)CD127 (1.27)VISTA (1.25)PD-L1 (1.24)4-1BB (1.21)*FDR p-value &lt; 0.05 (otherwise, p-value &lt; 0.05). Table 2: Predictors of RCB response

Overall populationHigher in RCB 0/1HER2* (fold-change 3.75)PD-L1 (1.25)Higher in RCB 2/3ER alpha* (2.44)Bcl-2 (1.46)HR+/HER2+ patientsStroma compartmentTumor compartmentHigher in RCB 0/1HER2* (fold-change 4.28)HER2* (4.21)CTLA4 (1.64)Higher in RCB 2/3Bcl-2* (2.18)*FDR p-value &lt; 0.05 (otherwise, p-value &lt; 0.05).HR-/HER2+ patients are not shown in Table 2 as only 2 HR- patients had unfavorable RCB response.

Citation Format: Adrienne G. Waks, Ying Huang, Tyler Hether, Esther R Ogayo, Sapana Kadel, Jillian Alberti, Sara M Tolaney, Ian E Krop, Prajan Divakar, Otto Metzger, Madison L O'Donnell, Sarah Church, Eric P Winer, Jennifer L. Guerriero, Elizabeth A Mittendorf. Correlation of immune-related protein expression with hormone receptor (HR) status and pathologic response to neoadjuvant paclitaxel/trastuzumab/pertuzumab (THP) among patients with early-stage HER2+ breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-07-03.