Modulation of the immune microenvironment in high risk DCIS

Background. Ductal carcinoma in situ (DCIS) is a risk factor for the subsequent development of invasive breast cancer. Features of DCIS that are associated with a high risk of a subsequent event include large size (\u003e 5 cm), high grade, comedo necrosis, palpable mass, hormone receptor negativity, and HER2 positivity. We have previously shown that immune infiltrates in DCIS are positively associated with these high-risk features, suggesting that manipulating the immune microenvironment in high risk DCIS could potentially alter disease progression. Objectives. The objectives of this study were: 1). to define dose limiting toxicities, tolerability, and feasibility of intralesional injection of an immune checkpoint inhibitor (pembrolizumab) into DCIS; and 2). to determine response rate as measured by an increase in total T cells or CD8+ T cells from baseline to post treatment. Methods. Study participants received 2 intralesional injections of pembrolizumab, 3 weeks apart, with surgery approximately 3 weeks after the 2nd dose. Multiplex immunofluorescence analyses were used to compare immune cell populations in pre-treatment biopsies to post-treatment surgical specimens. Tissue samples were stained with two 6-plex immune panels using Opal immunofluorescence reagents (Perkin Elmer) on a fully automated Ventana Discovery platform, imaged with a Vectra 3 system and analyzed with inForm software (Perkin Elmer). Results. The intralesional injections were well tolerated and there were no systemic toxicities observed. Multiplex immunofluorescence analyses demonstrated significant increases in total T cells, as well as cytotoxic CD8+ T cells, following therapy. We also observed a significant positive correlation between the change (pre- vs. post-therapy) in Ki67+ T cells (proliferating T cells) with the increase in total T cells, suggesting that immune checkpoint inhibition removed the “brakes” from the T cells, allowing them to proliferate. Changes in macrophage, B cell, and Treg numbers pre- vs. post-therapy were not significant. Despite an increase in T cell infiltrates, there were no measurable indicators of an anti-tumor response: no reduction in lesion size by MRI, no reduction in proliferation of DCIS cells (Ki67 staining), and no increase in cell death (cleaved caspase 3 staining). Spatial analyses indicated that in most cases the T cell expansion (both total T cells and CD8+ T cells) occurred predominantly in the stroma, not among the DCIS cells in the ducts. Conclusions. We met the objectives of our study: 1). we demonstrated the safety and feasibility of intralesional injection of an immune checkpoint inhibitor (pembrolizumab) in high risk DCIS; and 2). we demonstrated that local immunotherapy resulted in the local proliferation/expansion of T cells. However we did not observe any change in the size of the lesions by MRI. In addition, there was no evidence for T cell killing at the cellular level, suggesting that even though there was an expansion of T cells, there are other factors at play such as immune exclusion or possibly immunosuppression of their killing ability. These results suggest that combination of pembrolizumab with another agent(s) will be needed to achieve a more complete response. Citation Format: Michael Campbell, Jasmine Wong, Emma McCune, Harriet Rothschild, Tristan Loveday, Jennifer Bolen, Cliff Hoyt, Scott VandenBerg, Jo Chien, Laura Esserman. Modulation of the immune microenvironment in high risk DCIS [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-09-11.