In the current single-center study, 70 cases of OC patients administered with pelvic RT were retrospectively reviewed. Our data revealed that pelvic RT exhibited remarkable antitumor activity in OC patients without unpredictable adverse events. We reported a 2-year OS rate of 69.1% and a 2-year PFS rate of 34.8%, which corroborated with the findings of previous investigations (10, 11). The 3-year LC rate was 75.5%, supporting recent studies documenting that RT yielded satisfying local control outcome in OC patients (10, 12, 13). Besides, in agreement with other researches (14, 15), survival after RT had no correlation with platinum sensitivity at the onset of RT, indicating that RT could serve as an effective modality in the treatment of OC patients irrespective of platinum status.
Univariate and multivariate cox regression models were constructed in an attempt to locate potential beneficiaries of pelvic RT. Concerning histology, we observed that NHGSC was a favorable prognostic factor. Rare histology variants, such as ovarian clear cell carcinoma (OCCC), was particularly chemo-resistant with a clinical response rate to platinum-based CT of merely 18% (16, 17), and chances of curability of this subtype could be enhanced by adjuvant RT (18). Brown AP et al. documented that OCCC patients had a higher 5-year OS rate (88% vs 37%) and PFS rate (75% vs 20%) compared with other patients (10). Among the 5 OCCC patients in our series (Supplementary table 2), 2 patients progressed within 1 year and another patient progressed 36 months after RT. Only 1 patient died 43 months after RT and 4 other patients were still alive at the last follow-up, rendering improved PFS and OS time. Collectively, early and aggressive RT ought to be employed in the management of patients diagnosed with OCCC.
In the current study, early stage disease (FIGO stage I & II) and more CT regimens before RT predicted a longer PFS rate and OS rate. It is a well-acknowledged fact that advanced stage OC patients recurred after a median interval of 18–24 months and had a poor 5-year OS rate of 31% for stage III, 13% for stage IV (14), respectively, compared with early stage disease. This finding is inconsistent with that of Robert Rome et al. who observed significant correlation between initial stage I & II and disease specific death (19). However, prior investigations have shown that patients with stage III OC could still gain benefit from adjuvant intensity modulated whole-abdominal radiotherapy although more aggressive and accurate local management regimens are in urgent need (7). Regarding numbers of prior CT regimens, our finding is contrary to previous study which suggested that patients exposed to one prior CT regimens showed longer duration of survival than those administered with more prior CT regimens (15). The reason why numbers of CT cycles before RT was identified as a prognostic factor remains uncovered, and further mechanistic research should be undertaken to explore the underlying mechanism. It's highly likely that this result could be a statistical anomaly due to the limited number of patients enrolled in our retrospective study.
Furthermore, adjuvant RT after first relapse could markedly extend PFS period, but the OS benefit had not been observed according to our result. Westhoff et al. also found a prolonged PFS in 10 patients received RT for the first recurrence compared with those received it for subsequent recurrence (20). Additionally, we also reached the conclusion that adjuvant RT improved PFS period for OC patients during initial treatment. However, we didn't compare the toxicity and survival differences between post-operative adjuvant RT, adjuvant CT alone, and sequential chemoradiotherapy at initial treatment, which was in demand for in-depth investigations to confirm and validate these findings. Thus, we are unable to comment on the superiority of adjuvant RT over adjuvant CT for initial treatment from the results obtained in this study.
Several limitations to this study need to be acknowledged. First, it was a single-center experience and the sample size was relatively small. Second, it is possible that the results were biased, given the nature of retrospective design. Selection biases might occur when gynecologic oncologists recommended adjuvant pelvic RT. Finally, patients' economic conditions and medical literacy would exert a large effect on treatment choice. Hence, definitive large clinical trials are awaited regarding suitable OC patients for adjuvant pelvic RT.
In conclusion, pelvic RT might be a promising treatment option for OC patients, regardless of the platinum-sensitivity status. Patients with early stage disease, NHGSC, experiencing initial treatment and first recurrence, receiving more CT cycles are good candidates for adjuvant pelvic RT. Further investigations are warranted to confirm and validate these factors in terms of choosing treatment for OC patients.