Preoperative Chemoradiotherapy plus Nivolumab before Surgery in Patients with Microsatellite Stable and Microsatellite Instability-High Locally Advanced Rectal Cancer

Abstract

Purpose: Preoperative chemoradiotherapy (CRT) and surgical resection are the standard treatment for locally advanced rectal cancer (LARC). Combining immune checkpoint inhibitors with radiation suggests a promising approach for enhancing efficacy. We investigated the efficacy of CRT followed by nivolumab and surgery in patients with LARC.

Patients and methods: In phase I, we investigated the feasibility of sequentially combined CRT, 5 cycles of nivolumab, and radical surgery. In phase II, patients with microsatellite stable (MSS) and microsatellite instability-high (MSI-H) LARC were evaluated.

Results: Three patients in phase I received full courses of CRT and nivolumab without dose modification; the schedule was recommended for phase II. A pathologic complete response (pCR) was centrally confirmed in 30% [11/37; 90% confidence interval (CI), 18%-44%] and 60% (3/5) of the MSS and exploratory MSI-H cohorts, respectively. While immune-related severe adverse events were observed in 3 patients, no treatment-related deaths were observed. In 38 patients with MSS who underwent surgery, pCR rates of 75% (6/8) and 17% (5/30; P = 0.004, Fisher exact test) were observed in those with programmed cell death ligand 1 (PD-L1) tumor proportion score ≥1% and <1%, respectively; IHC staining was performed using pre-CRT samples. In 24 patients with MSS, pre-CRT samples were analyzed by flow cytometry; pCR rates of 78% (7/9) and 13% (2/15; P = 0.003, Fisher exact test) were observed for CD8+ T cell/effector regulatory T cell (CD8/eTreg) ratios of ≥2.5 and <2.5, respectively, in tumor-infiltrating lymphocytes.

Conclusions: CRT followed by consolidation nivolumab could increase pCR. PD-L1 expression and an elevated CD8/eTreg ratio were positive predictors in patients with MSS LARC.

Figure 1.

Representative effects of preoperative chemoradiation plus consolidation nivolumab monotherapy. Swimmer's plot of overall survival. From January 2017 to October 2019, a total of 39 patients with microsatellite stable (MSS) locally advanced rectal cancer (LARC) and 5 patients with microsatellite instability-high (MSI-H) LARC were enrolled. Radical surgery was performed for all patients, excluding one patient who declined surgery after achieving a near-complete clinical response with nivolumab. As of December 2020, six patients with MSS LARC experienced recurrence (two local and four distant), and no patients with MSI-H LARC experienced recurrence after a median follow-up of 32.9 and 17.2 months, respectively. One patient with MSS LARC died. The patient who achieved a near-complete clinical response and declined surgery experienced local regrowth and distant metastasis after 18.3 months of follow-up; there was no option for curative resection due to the multiple distant metastases.

Figure 2.

Comparison of effector regulatory T (eTreg) cells and CD8⁺ T cells in tumor infiltrating lymphocytes (TILs) between responders and non-responders. A, Peripheral blood mononuclear cells (PBMCs) and TILs were collected from 24 patients with microsatellite stable (MSS) locally advanced rectal cancer (LARC) who were enrolled in the VOLTAGE and subjected to flow cytometry. Representative flow cytometry plots are shown. Based on the expression levels of the naive T-cell markers CD45RA and FOXP3, we defined naive Treg cells (CD45RA⁺FoxP3^loCD4⁺) (I), effector Treg (eTreg) cells (CD45RA⁻FoxP3^hiCD4⁺) (II), and non-Treg cells (CD45RA⁻FoxP3^loCD4⁺) (III). B, Percentage of eTreg cells in CD3⁺ T cells of TILs in patients who achieved tumor regression grade (TRG) 2–3 and in patients who achieved TRG 0–1 at four time points (pre-CRT, post-CRT, post-3 cycles of nivolumab, and post-5 cycles of nivolumab) is shown. The median and interquartile range of TRG 0–1 and TRG 2–3 patients per group, respectively, are shown. The differences between the two groups of patients were compared using a Mann-Whitney U test. C, The CD8⁺ T cell/eTreg cell (CD8/eTreg) ratios in TILs in patients who achieved pathologic complete response (pCR) and in patients who achieved non-pCR at the pre-CRT time point are shown. The differences between the two groups of patients were compared using a Mann-Whitney U test. D, The CD8/eTreg ratios in TILs in patients who achieved pCR and in patients who achieved non-pCR at four time points (pre-CRT, post-CRT, post-3 cycles of nivolumab, and post-5 cycles of nivolumab) are shown. The median and interquartile range of pCR and non-pCR patients per group, respectively, are shown. The differences between the two groups of patients were compared using a Mann-Whitney U test. Naive (CCR7⁺CD45RA⁺); CM, central memory (CCR7⁺CD45RA⁻); EM, effector memory (CCR7⁻CD45RA⁻); TEMRA, terminally differentiated effector memory (CCR7⁻CD45RA⁺).

Figure 3.

Ki-67, PD-1, and CTLA-4 expression by CD8⁺ and CD4⁺ T cells in TILs in MSS LARC group and TMB in both the MSS LARC and MSI-H LARC groups. A, Ki-67, PD-1, and CTLA-4 expression by CD8⁺ T cells in tumor infiltrating lymphocytes (TILs) in patients who achieved tumor regression grade (TRG) 0–1 and in patients who achieved TRG 2–3 at pre-CRT are shown. The differences between the two groups of patients were compared using a Mann-Whitney U test. B, PD-1 expression by both CD8⁺ T cells and effector memory cells (T_EM) in TILs in patients who achieved TRG 0–1 and in patients who achieved TRG 2–3 at both the pre-CRT and post-CRT time are shown. The differences between the two groups of patients were compared using a Mann-Whitney U test. Because PD-1 expression could not be correctly evaluated during nivolumab therapy due to crossing with the PD-1 antibody, the data obtained after nivolumab therapy are not shown. C, CTLA-4 expression by both CD8⁺ T cells and the T_EM subset in TILs in patients who achieved TRG 0–1 and in patients who achieved TRG 2–3 at four time points (pre-CRT, post-CRT, post-3 cycles of nivolumab, and post-5 cycles of nivolumab) are shown. The differences between the two groups of patients were compared using a Mann-Whitney U test. D, CTLA-4 expression by both CD4⁺ T cells and the T_EM subtype in TILs in patients who achieved TRG 0–1 and in patients who achieved TRG 2–3 at four time points (pre-CRT, post-CRT, post-3 cycles of nivolumab, and post-5 cycles of nivolumab) are shown. The differences between the two groups of patients were compared using a Mann-Whitney U test. E, The tumor mutational burden (TMB) in pre-CRT samples in patients with microsatellite instability-high (MSI-H) locally advanced rectal cancer and in patients with microsatellite stable (MSS) LARC is shown (median 13.2/Mbp vs. median 0.99/Mbp). The differences between the two groups of patients were compared using a Mann-Whitney U test. F, The TMB in pre-CRT samples in patients with MSS LARC who achieved TRG 0–1 (median 1.45 mutations/Mbp) and in patients who achieved TRG 2–3 (median 0.84 mutations/Mbp) is shown. The differences between the two groups of patients were compared using a Mann-Whitney U test. T_EM, effector memory (CCR7⁻CD45RA⁻).