Currently, According to GLOBOCAN2020 data, cervical cancer (CC) accounts for approximately 6.5% of all malignant tumors in women worldwide, making it the fourth most common cancer among women (Sung et al., 2021). Cervical squamous cell carcinoma (CSCC) and cervical adenocarcinoma are the most common subtypes of CC, accounting for 70% and 25% of all cases, respectively (Guo et al., 2018; Jenkins et al., 2020). It is undeniable that newer screening, awareness and technology have reduced the growth of CC in the past decade (Sung et al., 2021). Due to the low coverage of CC screening in middle-and low-income countries, a considerable number of patients are diagnosed with locally advanced cervical cancer (LACC) at the first diagnosis, including patients with stage IB3-IVA disease (Serkies and Jassem, 2018). Since 1999, cisplatin-based CCRT has become the standard treatment for patients with LACC, for which the total effective rate is more than 90% (Rose et al., 1999). However, approximately 30%–50% of patients with CC still experience local recurrence or distant metastasis after undergoing CCRT (Rose et al., 1999; Kumar and Gupta, 2016). Therefore, determining the prognostic factors of patients with LACC treated with CCRT is highly important.

Many studies have shown that PUFAs act vital roles in the occurrence of malignant tumors, including in the regulation of apoptosis (Haycock et al., 2023; Montecillo-Aguado et al., 2023). Omega-3 PUFAs are one of the polysaturated fatty acids, that are derived mainly from deep-sea fishes, such as sardines and herring, thus, they are also known as marine PUFAs (Montecillo-Aguado et al., 2023). It has been widely reported in epidemiological studies because of its remarkable anti-inflammatory effects, direct inhibition of cancer expansion and tumorigenesis (Vaughan et al., 2013; Wei et al., 2022). Omega-3 PUFAs mainly include eicosapentaenoic acid (C20:5, EPA), docosahexaenoic acid (C22:6, DHA) and docosapentaenoic acid (C22:5, DPA), among them, EPA and DHA have the highest biological activity. DPA are the intermediates of DHA and EPA and may also have potential anticancer properties (Vaughan et al., 2013).

Andrew et al. reported that EPA has significant anti-angiogenic effects on colorectal cancer, and that high levels of EPA could improve overall survival (OS) (Cockbain et al., 2014). A meta-analysis of 20 studies showed that omega-3 PUFAs significantly improved nutritional status and immune function in patients with colorectal cancer after radical resection after strict control of bias risk (Yue et al., 2022). Endogenous omega-3 PUFAs enrichment can reduce cisplatin-induced myelosuppression by regulating the NRF2-MDM2-p53 signaling pathway (Xu et al., 2023). Interestingly, the introduction of omega-3 PUFAs in esophageal, colorectal and breast cancer has been gradually proven to enhance the cytotoxicity of some chemotherapeutic drugs and enhance the sensitivity of tumors to ionizing radiation, but does not increase the toxicity to normal tissues (Cai et al., 2014; Shin et al., 2019; Yang et al., 2022). Kai and other researchers have showen that the unsaturation of exogenous fatty acids is positively correlated with ferroptosis sensitivity. DHA can effectively promote ferroptosis by mediating intracellular lipid peroxidation to kill CC HeLa cells (Shan et al., 2022). Supplementation with omega-3 PUFAs is effective at maintaining skeletal muscle mass, nutritional status and reducing toxicity from radiotherapy in CC patients (Aredes et al., 2019). However, the effect of pretreatment plasma omega-3 PUFAs levels on the clinical outcome of patients with CSCC who underwent CCRT has not been reported thus far. Therefore, predicting the survival rate by measuring the levels of omega-3 PUFAs before treatment in patients with CSCC who underwent CCRT may be helpful for evaluating patient prognosis.

The purpose of this experiment was to assess the predictive value of omega-3 PUFAs levels for early treatment response, progression-free survival (PFS), and overall survival (OS) in patients with CSCC who were undergoing CCRT.

This study was approved by the Ethics Committee of the Second Affiliated Hospital of Dalian Medical University.

In view of the poor prognosis of patients with CC and the high tumor recurrence rate after CCRT, it is necessary to screen the risk factors of tumor prognosis and recurrence in order to support early intervention, improve monitoring, reduce tumor recurrence rate and prolong patient survival time. As lipids are closely related to tumorigenesis or tumor recurrence, marine polyunsaturated fatty acids (omega-3 PUFAs) as an important lipid, it is necessary to understand whether there is a relationship between omega-3PUFAs and the response and prognosis of patients with CC who underwent CCRT. This is the first study to evaluate the association between omega-3 PUFAs and response and prognosis in patients with CSCC who received CCRT.

Previous in vivo and in vitro studies have found that in addition to its direct cytotoxic effects on tumor cells, EPA can increase the cytotoxicity of anticancer drugs to tumors or cancer cells, even at doses that have no substantial effect on tumor growth or cell viability (Bégin et al., 1986; Bégin et al., 1988). Early experiments have proven that omega-3 PUFAs represented by EPA can enhance the sensitivity of breast, colorectal and ovarian cancers and other tumors to anticancer drugs, and have cytotoxicity to both vincristine-sensitive and drug-resistant human CC cells, which can increase the killing effect of human CC cells by 30%, and increase cisplatin’s cytotoxicity against cytotoxicity of cisplatin on human CC cells by 36%–60% (Das et al., 1998; Hajjaji and Bougnoux, 2013). Consistent with these findings, our study found that both univariate and multivariate analysis results showed that patients who achieved CR in patients with CSCC who underwent CCRT had higher pretreatment levels of EPA. This finding suggested that a high level of EPA before treatment is an independent predictor of CR after CCRT. We suspect the mechanism might be EPA is the main starting substance of lipid peroxidation. With the increase in EPA concentration, the level of lipid peroxide produced by cells increased significantly, which was related to the loss of cell vitality and the significant inhibition of cell growth (Falconer et al., 1994). EPA treatment promotes the production of large amounts of ROS, which are highly peroxidizable and therefore may enhance the efficacy of cytotoxic ROS-inducing drugs against tumors (such as anthracycline, mitomycin, etc.) (Das et al., 1998; Colquhoun, 2009; Moon, 2023). Since ionizing radiation also generates ROS, which leads to lipid peroxidation of PUFAs, lipid peroxidation may be further enhanced in the membranes of EPA-rich tumor cells, and thus the combination of EPA and radiotherapy may cause additional damage to tumor cells (Manda et al., 2011; Zaloga, 2021). This seems to provide a strong explanation for the fact that EPA can enhance the sensitivity of radiotherapy and chemotherapy.

Regarding the relationship between EPA and tumor prognosis has rarely been investigated, a phase II randomized, double-blind trial demonstrated that oral EPA significantly slowed the growth of colorectal liver metastases, the reason for which may be that EPA has antiangiogenic properties and limited preoperative EPA exposure may prolong disease-free survival (DFS) and OS (Cockbain et al., 2014). Murphy et al. also demonstrated that NSCLC patients treated with platinum-based chemotherapy taking 2.5 g of EPA + DHA supplementation per day had a twofold increase in clinical benefit and treatment response rate, and a higher 1-year survival rate for patients in the supplementation group (60% vs 38.7%), than patients who received standard treatment but no additional supplementation (Murphy et al., 2011). These studies are consistent with our results. We found that in patients with CSCC treated with CCRT, the level of plasma EPA ≥46.0 nmol/mL before treatment was significantly correlated with PFS (HR, 0.263; 95% CI, 0.089–0.782, p = 0.016). In multivariate Cox regression analysis, it was found that plasma EPA ≥46.0 nmol/mL before treatment was not an independent predictor of OS (HR, 0.288; 95% CI, 0.063–1.313, p = 0.108). However, the Kaplan-Meier survival curve showed that the OS of patients with plasma EPA ≥46.0 nmol/mL was better than that of patients with plasma EPA <46.0 nmol/mL before treatment. The reason for this phenomenon may be due to the small sample size and insufficient follow-up time. We will strive to collect more samples and conduct long-term follow-up for further research. However, in the univariate analysis of PFS and OS, the plasma DHA level ≥308.0 nmol/mL before treatment was statistically significant, p = 0.040 and 0.036, respectively, but in multivariate analysis, DHA level was not an independent prognostic factor for PFS and OS.

This study suggested that plasma EPA is a valid pretreatment biomarker for predicting survival in CSCC patients who underwent CCRT. However, the possible mechanism by which pretreatment plasma EPA reflects the prognosis of patients with CC as a new indicator for assessing OS and PFS is unclear. The preliminary explanation can only be given by considering previous studies. The anticancer effects of EPA are mainly attributed to its ability to modulate cell death pathways, inhibit cell proliferation and induce the expression of anti-inflammatory mediators (D'Angelo et al., 2020; Montecillo-Aguado et al., 2023). The mechanism by which EPA promotes apoptosis alone involves the alteration of multiple complex cellular pathways; for example, EPA was able to induce cell cycle arrest in breast cancer cell lines (Zhu et al., 2018). In particular, the progression of the cell cycle from the S to the G2-M phase was blocked in BT20 breast cancer cells, and this apoptotic effect was shown in a concentration- and time-dependent manner (Nappo et al., 2012). Similarly, it inhibits cholesterol efflux channel protein (ABCA1), leading to intracellular cholesterol accumulation and thus dysregulation of cholesterol homeostasis, which in turn increases cell membrane polarity lethality in triple-negative breast cancer cells (Torres-Adorno et al., 2019).

As a tumor marker, SCC-Ag is widely used in CSCC, and the increase of SCC-Ag before treatment is associated with larger tumor size, late tumor stage, regional lymph node involvement and deep stroma involvement, so it is widely used in monitoring CC recurrence (Wang et al., 2019). However, there are few studies on the relationship between SCC-Ag and the prognosis of CC. Wang et al. included 559 patients with CSCC. Multivariate analysis showed that SCC-Ag did not decrease to normal after CCRT was an independent prognostic factor for DFS (HR, 5.10; 95%CI, 3.31–7.88, p < 0.001) (Wang et al., 2019). This is highly consistent with our results, which show that post SCC-Ag level>2.5 ng/mL is an independent risk factor for 3-year PFS (HR, 3.148; 95%CI, 1.138–8.706, p = 0.027). Interestingly, we found that there was a negative correlation between pre SCC-Ag and EPA (r = −0.305, p = 0.004),a weak negative correlation between post SCC-Ag and EPA (r = −0.251, p = 0.018) and the survival probability of patients in the pretreatment plasma EPA≥46.0 nmol/mL and post SCC-Ag≤2.5 ng/mL groups had the highest probability of survival, and patients with pretreatment plasma EPA<46.0 nmol/mL and post SCC-Ag>2.5 ng/mL had the lowest survival rate among the four groups. These results further confirmed the inverse relationship between EPA and SCC-Ag. Recent studies have also shown that EPA can significantly reduce the levels of serum TNF- α and IL-6 in tumor patients. At the same time, EPA can reduce the level of inflammatory reaction and improve body immune function by reducing the production of C-reactive protein and limiting the release of IL-6 (Liu et al., 2023). It is suggested that the expression levels of EPA and post SCC-Ag may be auxiliary markers for monitoring disease progression and tumor malignancy. However, we found that FIGO staging was a significant predictor of PFS in univariate analysis, but its significance was not significant in multivariate analysis. One of the reasons for this phenomenon may be the insufficient number of cases studied, and the lack of stage IVA patients in our group may also be.

EPA has a wide range of molecular targets in cancer cells and tumors. To sum up, the results show that EPA can activate a variety of molecular biological processes, including classical and alternative apoptosis pathways, and regulate survival and cell growth signals. Causing cell death in a variety of cells and animal models. However, further experiments are needed to explore the specific details of external approaches, especially upstream events. These findings suggest that EPA is expected to be a potential new treatment for cancer and can complement existing treatments. However, our clinical study further validates these basic experiments. In conclusion, the above mechanisms may partially explain why pretreatment plasma EPA may be a biomarker of outcome and prognosis in patients with CSCC who underwent CCRT. This study showed that the abnormal level of plasma EPA before treatment is directly related to the response and survival outcome of patients with CSCC receiving CCRT, and the level of plasma EPA before treatment can be used as a biomarker to assess the response and prognosis of CSCC patients.

However, our study also has some limitations. First, as a small-sample retrospective study, we regret that we were unable to accurately and dynamically track the level of changes in omega-3 PUFAs during and at the end of CCRT. Second, this study did not examine the relationship between nutritional support therapy and omega-3 PUFAs levels. Finally, the patients we enrolled were all patients with CSCC, and the results may be biased when it comes to patients with types of cervical adenocarcinoma and adenosquamous carcinoma. In the future, it is necessary to further elucidate the specific molecular mechanisms of the regulation of apoptosis, proliferation, survival, migration and drug resistance of omega-3 PUFAs, including the specific pathways involved and the interactions between different PUFAs. In addition, more research is needed to investigate the effects of omega-3 PUFAs on different types of cancer cells and animal models, and to evaluate their potential synergies with existing cancer therapies. However, it is unclear whether there is a clear benefit of elevated EPA levels after supplemental therapy, and if their beneficial effect is confirmed to improve local control of cervical cancer through dietary lipids as an adjunctive to CCRT, the prospects for systemic supplementation during CSCC treatment would be considerable.

In conclusion, the present study demonstrated that pretreatment plasma omega-3 PUFAs are associated with survival outcomes in patients with CSCC treated with CCRT. Pretreatment plasma EPA may be a promising biomarker for predicting recent response and PFS in patients with CSCC who underwent CCRT. The use of plasma EPA level before treatment and serum SCC-Ag level after treatment increased the prognostic significance of serum SCC-Ag level alone. Perhaps it is preferable to use a system of two or more determinants to create new prognostic tools for clinicians in CSCC. As an independent factor, EPA can be used as a new and promising prognostic index, which can be detected routinely and conveniently and cheaply, which will provide potential prognostic information for clinicians to promote individualized treatment of patients with CSCC.