Tumor Microenvironment before and after Chemoradiation in Locally Advanced Rectal Cancer: Beyond PD-L1

Localized rectal cancer is currently managed with neoadjuvant therapy before surgery which includes concurrent chemoradiation therapy alone or a total neoadjuvant therapy approach which involves chemotherapy and concurrent chemoradiation sequentially. These strategies are changing, and optimal management of rectal cancer continues to evolve. Immunotherapy has entered the treatment paradigm in advanced rectal cancer for patients with microsatellite instability. A role for immunotherapy for early-stage disease has yet to be established. Clinical trials in rectal cancer incorporating immunotherapy in the neoadjuvant settings are underway however better understanding of the tumor microenvironment and targeting specific biomarkers may be more efficacious. In this paper, we report on rectal cancer tumor microenvironment changes following neoadjuvant chemoradiation. Identifying changes in biomarker expression within the tumor microenvironment may be predictive of better outcomes, improved response to immunotherapy and may also identify new targets which could lead to targeted therapeutic drug development. Background: In locally advanced rectal cancer treatment, neoadjuvant concurrent chemoradiation therapy (cCRT) is the standard of care. The tumor microenvironment (TME) is a complex entity comprising of tumor cells, immune cells and surrounding stroma and is closely associated with tumor growth and survival, response to antitumor therapies and also resistance to treatment. We aimed to assess the change in biomarkers associated with TME following standard neoadjuvant cCRT in rectal cancer. Methods: We accessed archival tissue from rectal cancer patients treated with neoadjuvant cCRT at Allegheny Health Network (AHN) facilities over the past 14 years. Pretreatment and post-treatment biopsies were assayed for PD-L1, CD8+ T-cells, CXCL9, TIM-3, IDO-1, IFN-G, IL17RE, LAG-3, and OX40 in 41 patients. Results: We found statistically significant upregulation in multiple biomarkers namely CD8, IL17RE, LAG3 and OX40 post neoadjuvant cCRT and a trend towards upregulation, although not statistically significant, in biomarkers PD-L1, CXCL9, TIM-3, IDO-1 and IFN-G expression. Conclusions: This provides a glimpse into the TME before and after neoadjuvant cCRT. We suggest that the biomarkers noted to be upregulated could be used for designing appropriate clinical trials and development of therapeutic targeted drug therapy in an effort to achieve better response to neoadjuvant therapy, increasing clinical and pathological complete response rates and improved overall outcomes.