Whether NACT-IDS is noninferior to PDS regarding patient prognosis has been a controversial topic. Approximately 82% of SGO members did not consider that there is sufficient evidence to justify NACT [26]. Despite this, the utility of NACT in the United States increased from 7.7% in 2004 to 27.8% in 2015 [27]. Currently, the National Comprehensive Cancer Network (NCCN), FIGO and ESMO guidelines have recommended NACT-IDS as an alternative option for ovarian cancer patients with advanced disease [2, 15, 28]. NACT can decrease tumor volume, thereby allowing for a less traumatic surgery and a higher R0 resection rate [24]. However, this treatment exposes a high tumor burden to chemotherapeutic drugs, which results in a selection of resistant tumor clones [29, 30]. Even among HGSC patients with BRCA1-heterozygous tumors that are supersensitive to DNA-damaging drugs and poly (ADP-ribose) polymerase (PARP) inhibitors, the utility of NACT is observed to facilitate the expansion of pre-existing BRCA1-proficient tumor clones [31]. In addition, there have been clinical data suggesting that NACT patients are more likely to develop platinum-resistant recurrence [32, 33]. The Japan Clinical Oncology Group phase III RCT 0602 (JGOG0602) compared NACT-IDS with PDS [34]. In 2020, the authors reported that the survival noninferiority of NACT was not validated in the trial [34]. At the Annual Meeting of ASCO in 2020, using data from the PAOLA-1 trial, C. Grimm et al. reported that among ovarian cancer patients receiving olaparib plus bevacizumab as maintenance therapy, the magnitude of PFS benefit was lower in NACT patients treated with NACT than in patients treated with PDS [35]. Collectively, these findings remind us of the potential negative influence of NACT. NACT should only be reserved for those who are poor surgical candidates and/or who have unresectable disease [24]; following NACT, patients should be stratified according to their prognosis so they can have a better opportunity to gain a survival benefit from more individualized management.
The CRS system was proposed by Böhm and colleagues in 2015 [16]. It can divide HGSC patients who receive NACT according to their response: complete/near complete (CRS3), partial (CRS2), and no/minimal (CRS1) responses. Since the survival outcomes of the CRS1 patients were similar to those of the CRS2 patients, CRS can actually be treated as a binary prognostic system that stratifies patients into two subgroups [16, 21]. Herein, we observed that CRS3 could be achieved in 22.6% of NACT patients, and this cohort had a significantly decreased risk of recurrence compared with those who achieved CRS1-2. These results are consistent with those of previous studies and confirmed that the CRS system can be used as a reliable tool for prognostic stratification [19, 21]. In the study by the HGSC CRS Collaborative Network, more patients in the CRS3 group were noted to have a germline BRCA 1/2 mutation than those in the CRS1-2 group [19]. Therefore, CRS3 following NACT may suggest a favorable tumor biology, which provides a possible explanation for why CRS3 patients benefit more from NACT than the others.
In the neoadjuvant setting, CA125 can be utilized as a marker to assess the response to chemotherapy. The post-NACT CA125 level can predict the possibility of achieving optimal cytoreduction in IDS [36–38]. Despite this, the CA125 response does not exactly equate to the pathological response [16, 19]. As we observed, CA125 normalization was noted in 70.83% of patients achieving CRS3. We identified the normalization of CA125 following NACT as an independent predictor of decreased recurrence risk. Even in the CRS3 subgroup, patients with post-NACT CA125 ≤ 35 U/ml were observed to have a longer median PFS than those with post-NACT > 35 U/ml, which was further confirmed in the Cox analysis. These findings were not completely consistent with those in previous studies [36, 39–42]. However, given the following limitations in previous studies, caution must be taken in interpreting their results. First, many of the published studies included patients with non-serous epithelial cancer patients, yet the prognostic value of CA125 for these patients remains controversial [43]. Second, there is convincing evidence that NACT will exert a negative effect on patient prognosis if the number of NACT cycles exceeds four [42, 44]. Although previous studies included patients receiving more than four cycles of NACT, the researchers did not consider or adjust the impact of the number of chemotherapy cycles. In light of these limitations, we believe that our findings complement those of prior studies and provide more reliable information regarding the prognostic role of CA125 normalization in NACT patients.
Since both the CRS system and the normalization of CA125 were independently associated with patient prognosis, we combined them and developed a new stratification method. Compared with the CRS system [16], the new method identified one more subgroup, the intermediate-risk group. Patients in the intermediate-risk group achieved CRS3 and received the same subsequent treatment as the other patients who achieved CRS3; however, they had a high risk of recurrence. The CRS system is based on omental assessment. Of note, the response of the omentum to NACT is not necessarily in line with that of other sites [16, 19]. Therefore, CRS3 patients are a heterogeneous group with varying tumor loads. Since the CA125 level is correlated with tumor burden in 93% of ovarian cancer patients [45], it could help identify the cohort of patients with a higher tumor load among the CRS3 patients, thereby complementing the CRS system in the prognostication of NACT patients.
The present study is the first one to explore the role of combining the CRS system and the CA125 level in an attempt to refine the prognostic stratification of HGSC patients who were treated with NACT. Given that the CRS and CA125 are readily available in clinical practice, we believe that our findings are easily applicable in the care of patients in resource-limited areas. Nevertheless, some limitations of the current study should be acknowledged. First, as a retrospective study, missing data could not be avoided, so the adjustment variables entered in the multivariable analyses might be incomplete. Second, as information about BRCA 1/2 mutations was not available in most of the included patients, we could not conduct a more detailed subgroup analysis. Third, although the PFS of our cohort was in line with that of previous reports [16, 18], the follow-up period in the present study was relatively short, and the median OS was not reached. Finally, the sample size of this work is limited. The data of the present study were collected from two tertiary-referral university hospitals in China. The clinical decisions in our institutions are made in accordance with the ASCO-SGO guidelines [24], and NACT has been prescribed to only carefully selected patients. Thus, although we pooled eight years of data, only 106 patients were included in the final analysis. As a result, it is not possible to perform a reliable validation.