Abstract A43: Induction of systemic immune response by oxaliplatin-based neoadjuvant therapy and survival without metastatic progression in high-risk rectal cancer
Authors: Kalanxhi Erta , Meltzer Sebastian , Schou Jakob Vasehus , Larsen Finn Ole , Dueland Svein , Flatmark Kjersti , Jensen Benny Vittrup , Hole Knut Håkon , Seierstad Therese , Redalen Kathrine Røe , Nielsen Dorte Lisbet , Ree Anne Hansen 
Published: February 2019

In locally advanced rectal cancer (LARC), local recurrence rates are low due to contemporary multimodal treatment regimens involving neoadjuvant chemoradiotherapy (CRT) and surgery. Metastatic progression however, represents a major challenge and is reported by 30-40% of cases in recent trials. Ongoing effort to combine treatment modalities, including immunotherapy, to best target systemic progression of colorectal cancer, would benefit from a better understanding of the biological and immune responses invoked from the different treatment modalities.

In this report we investigated systemic immune activity invoked in LARC patients undergoing neoadjuvant regimens containing oxaliplatin (an agent known to cause immunogenic cell death), by assessing circulating levels of the fms-related tyrosine kinase 3 ligand (Flt3L). Flt3L is a potent hematopoietic factor with proliferating effects on mature dendritic cells (DC), whose elevated levels have also been demonstrated to reflect therapy-induced myelosuppression. LARC patients with mainly T3-4 disease from two independent cohorts (Oslo and Copenhagen) received neoadjuvant chemotherapy (NACT) and sequential CRT. All of the Oslo cohort patients underwent NACT consisting of 4 weeks of the Nordic FLOX regimen (oxaliplatin 85 mg/m2 on day 1 and bolus fluorouracil 500 mg/m2 and folinic acid 100 mg on days 1 and 2 every second week) followed by long-course CRT (radiation to a total dose of 50 Gy and concomitant weekly oxaliplatin 50 mg/m2 and capecitabine 825 mg/m2 twice daily), and then surgery 8-12 weeks later. Eighty percent of Copenhagen cohort patients underwent NACT as 6-8 weeks of oxaliplatin 85 mg/m2 every second week and continuous capecitabine 650 mg/m2 twice daily. Less than 90% of patients had concomitant weekly oxaliplatin 50 mg/m2 during the long-course CRT to a total radiation dose of 54 Gy. Finally, 57% of patients received an additional 1-2 cycles of capecitabine with or without oxaliplatin following CRT completion. Patients had surgery 2-19 weeks after CRT completion. In both cohorts, Flt3L levels were measured in serum collected at baseline, following NACT and then the sequential CRT. Serum samples were stored at –80°C until analysis and Flt3L was quantified using ELISA or a customized Luminex Multiplex Assay (both from R&D Systems). In 39 randomly chosen samples covering all three sampling points, a strong correlation (r=0.96, p&lt;0.01) was found between Flt3L levels measured by the single-parameter and multiplex assays.

We found that median serum Flt3L levels were elevated upon completion of each sequential modality in both cohorts (n=73 and n=65). In the principal cohort (Oslo), an increase in levels of Flt3L upon NACT completion was correlated with a decline in hemoglobin and neutrophil counts (r=–0.38, p&lt;0.01 and r= –0.36, p=0.01), possibly reflecting the myelosuppressive effect. Progression-free survival (PFS), with the majority of events being metastatic progression, was 68% and 71% in the two cohorts. For T4 cases in the Oslo cohort, a high Flt3L level following NACT was associated with a low risk for a PFS event (HR=0.22, 95% CI=0.06-0.72, p=0.01). Additionally, oxaliplatin dose reduction during CRT, aimed at maintaining patient compliance to radiotherapy, was also associated with advantageous PFS (HR=0.40, 95% CI=0.17-0.92, p=0.03).

In conclusion, the neoadjuvant regimens might have caused repetitive myelosuppression resulting in elevated circulating Flt3L levels, thereby enhancing proliferation of mature dendritic cells and mediation of systemic tumor-targeting effects. Oxaliplatin-containing neoadjuvant therapy that causes normal tissue toxicity but does not compromise patient compliance to the radiotherapy, may condition DC to present shed tumor antigens to cytotoxic T cells, and thus enable eradication of occult microscopic tumor at distant sites in LARC patients prone to develop metastatic disease.

Citation Format: Erta Kalanxhi, Sebastian Meltzer, Jakob Vasehus Schou, Finn Ole Larsen, Svein Dueland, Kjersti Flatmark, Benny Vittrup Jensen, Knut Håkon Hole, Therese Seierstad, Kathrine Røe Redalen, Dorte Lisbet Nielsen, Anne Hansen Ree. Induction of systemic immune response by oxaliplatin-based neoadjuvant therapy and survival without metastatic progression in high-risk rectal cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A43.