In this study, we sought to determine whether tumor immunity is associated with the treatment response to postoperative radiotherapy for cervical cancer by considering two independent cohorts, an NAC and a non-NAC group, to examine the impact of various factors related to tumor immunity. The 5-year RFS rate was 76.5% in all patients, 80.9% in the non-NAC group, and 72.2% in the NAC group, with no statistically significant differences found according to preoperative NAC. Considering that the NAC group included more advanced cases, this result suggests that NAC and CCRT were effective to some extent, but not enough to obtain markedly improved outcomes. To investigate the cause of these outcomes, this study evaluated differences in tumor immune response with and without NAC.
Our analysis revealed significantly lower pretreatment PD-L1 expression in the recurrence group than in the non-recurrence group among patients without NAC. We have previously reported that high PD-L1 expression is associated with favorable radiotherapy outcomes not only in cervical cancer but also in oropharyngeal and oral cancers (8, 11, 12). These findings agreed with the result of this study. In our studies, higher PD-L1 expression in tumor cells was associated with improved OS, which was in contrast to general expectations based on the known immunosuppressive effects of this ligand. This apparent paradox could be explained by the fact that tumor-infiltrating cytotoxic T cells upregulate PD-L1 expression and secrete interferon (IFN)-γ when they encounter tumor antigens, followed by an adaptive response to IFN-γ that further increases PD-L1 expression on tumor cells and neighboring infiltrating immune cells. Thus, PD-L1 expression can be considered a marker of an active host antitumor immune response [5]. In univariate analysis of the non-NAC group, histology, N stage, concurrent chemotherapy, and PD-L1 TC were significant prognostic factors related to RFS, whereas only PD-L1 TC remained significant in multivariate analysis. Thus, in the non-NAC group, a PD-L1–positive status, which indicated the presence of active tumor immunity, resulted in a better response to radiotherapy, suggesting that pretreatment tumor immunity has a significant impact on the treatment outcome. Conversely, histology, tumor size, presence of lymph node metastasis, and PD-L1 expression were not significant prognostic factors in the NAC group. This suggests that the effect of anticancer agents overcame, to some extent, clinical conditions that are otherwise associated with an adverse outcome, such as non-squamous cell carcinoma, large primary tumor, presence of lymph node metastasis, and inactive tumor immunity before treatment.
In the NAC group, PD-L1 expression was lower in the surgical specimens than in the preoperative biopsy specimens in most cases (11 of 14) and PD-L1 reduction was the only prognostic factor for poor RFS. This indicates that the tumor immunosuppressive effect of anticancer drugs could have a significant negative impact on survival. Accordingly, in the NAC group, the anticancer drugs may have offset the tumor immunosuppressive effects of the anticancer drugs, and the resulting in less improvement in the therapeutic outcome may not have been significantly improved. We previously performed immunohistochemical analysis of pre-radiotherapy biopsies and the corresponding post-radiotherapy resected tissues from 104 patients with cervical cancer who received preoperative radiotherapy [8]. The results of preoperative radiotherapy contrasted with those of the NAC in this study. PD-L1 TCs were significantly increased after radiotherapy; in surgical specimens obtained after radiotherapy, high PD-L1 TC expression was a significant predictor of longer OS and was associated with a significantly lower probability of both in- and out-of-field recurrence, suggesting that the immune system influences the control of both irradiated and non-irradiated tumor sites by enhancing the systemic antitumor immunity. Radiation therapy can induce immunogenic cell death, release neoantigens and human papillomavirus-derived antigens, induce the uptake of these antigenic components by dendritic cells, and activate T cell-mediated immunity through the expansion of antigen-specific cytotoxic T cells and the production of tumor-specific monoclonal antibodies [13]. Thus, NAC and radiotherapy may have different effects on tumor immunity.
We further found that host immune cell infiltration, including CD8+, FOXP3 + and CD11c + T cells, was not a significant factor contributing to RFS. The number of immune cells can be influenced by various factors, including disease stage and treatment received [14, 15]. In contrast, PD-L1 expression has been reported to be well-matched between primary tumors and metastases [16], suggesting that PD-L1 expression may be a more specific marker of tumor immunity than infiltrated immune cells.
The main limitations of this study were the relatively small sample size, heterogeneity of patient backgrounds, and the fact that there were two treatment regimens; thus, the results should be validated in an independent sample with these factors controlled. In addition, stage IIb is the point at which the standard of care changes from postoperative radiation to radical CCRT, which may have reduced the clinical impact of this study. In addition, the results of our image-based analyses of PD-L1 expression and infiltration of CD8-, FOXP3-, and CD11c-positive cells into tumors may need to be verified by an experienced pathologist. However, the fact that high PD-L1 expression was a significant positive prognostic factor in multivariate analysis in the non-NAC group and decreased PD-L1 expression was a negative prognostic factor in multivariate analysis in the NAC group suggests the possibility of combination of immunotherapy with immune checkpoint inhibitors and radiotherapy as an alternative to NAC. Immunotherapy has significantly improved the cure rate of patients in several cervical cancer clinical trials, demonstrating the synergistic effects of radiotherapy and immunotherapy [17].
In conclusion, we evaluated the relationship between PD-L1 expression in cancer cells and prognosis of cervical cancer patients treated with postoperative radiotherapy and the impact of NAC on these outcomes. We found that among the non-NAC group, patients with higher PD-L1 TCs (> 10%) had significantly better RFS than those with a lower number of PD-L1 TCs. This suggests that pretreatment tumor immune activation had a significant impact on the outcome of surgery and postoperative radiotherapy for cervical cancer. Moreover, within the NAC group, patients with a greater reduction in PD-L1 TCs after chemotherapy had a significantly worse prognosis. This suggests that NAC induces an immunological shift that decreases PD-L1 TC levels to negatively affect cervical cancer treatment outcomes.