Deciphering tumor microenvironment dynamics in HER2-amplified refractory metastatic colorectal cancer in the TRIUMPH trial.
Authors: Imai Mitsuho , Lim Jinyeong , Iida Naoko , Ebi Hiromichi , Okamoto Wataru , Kato Takeshi , Esaki Taito , Kato Ken , Komatsu Yoshito , Yuki Satoshi , Masuishi Toshiki , Nishina Tomohiro , Sato Akihiro , Yamashita Riu , Fujii Satoshi , Yoshino Takayuki , Park Woong-Yang , Nakamura Yoshiaki 
Published: June 2024

3564 Background: Approximately 2-4% of patients with metastatic colorectal cancer (mCRC) harbor HER2 amplification, a subset notorious for poor response rates following conventional treatments. The TRIUMPH trial introduces anti-HER2 therapy, combining trastuzumab and pertuzumab. Despite its potential, the observed response rate stands at 30%, accompanied by an early recurrence within 3.5 months with acquired resistance, which emphasizes the need for further investigations into resistance mechanisms within this patient population. Here, we delineate the dynamic changes in both the tumor and its microenvironment in response to treatment and mechanisms of acquired resistance using spatial transcriptomics. Methods: Within the TRIUMPH trial, a total of 20 formalin-fixed paraffin-embedded (FFPE) biopsy slides from 13 patients were collected before and after treatment or at one time. Utilizing these FFPE slides, we employed imaging-based single-cell spatial transcriptomics, using a custom panel tailored for the tumor and its microenvironment. This panel includes gene sets related to tumor growth, drug resistance, and immune response. Results: To comprehend the complexities of the tumor and its surroundings, we categorized tumor tissue into distinct sections, encompassing tumor, stromal, and immune-enriched areas based on their neighbor cells. Remarkably, we noted a substantial rise in the infiltration of T cells and myeloid cells into tumor-enriched regions post-treatment. T cells increased from a median of 1.5% to 2.2%, and myeloid cells from 4.3% to 7.4%, particularly in patients showing a response. Additionally, ERBB2 expression in tumor cells was high, whereas the non-response group exhibited lower expression levels. Prior to treatment, fibroblast and endothelial cells were intricately intertwined with tumor cells. However, subsequent to treatment, these cells segregated into stromal regions, exhibiting an increase in their proportions. Notably, angiogenic tumor-associated macrophage (angio-TAM), expressing SPP1 and VEGFA, were localized at the interface of tumors and stromal cells and proliferated following disease progression. This spatial reorganization signifies dynamic alterations within the tumor microenvironment following treatment. Conclusions: Our study on HER2-amplified metastatic colorectal cancer in the TRIUMPH trial uncovers intriguing spatial changes post anti-HER2 therapy. Notably, dynamic reorganization of fibroblast and endothelial cells into stromal regions suggest complex treatment responses. Identification of angio-TAM expressing SPP1 and VEGFA adds depth to understanding the contribution of tumor microenvironment to the resistance mechanism. These findings highlight the intricate tumor microenvironment shifts, urging further exploration for optimized therapeutic strategies.