The procedure for classic standard cytoreduction includes uterine and ovarian removal, omentectomy, appendectomy, lesions in the pelvic cavity and para-aortic lymphadenectomy [13]. According to the literature, postoperative survival time in patients who meet this criterion is significantly higher than in patients with unsatisfactory tumor reduction [14]. Lymphadenectomy is an important step in cytoreductive ovarian cancer, but it increases the duration of surgery, length of postoperative hospital stay cost of surgery and results in many postoperative complications due to the high incidence of pelvic and para-aortic lymph node metastasis [15]. There has resulted in a widespread debate about the need for lymph node dissection.

The first randomized clinical trial evaluating the role of lymphadenectomy in advanced ovarian cancer was reported in 427 patients with advanced ovarian cancer who underwent systemic lymphadenectomy or only resection of enlarged lymph nodes. Results suggested that lymphadenectomy significantly improved progression-free survival (29.4 months and 22.4 months) and reduced the rate of disease recurrence but did not improve overall survival (respectively 58.7 months and 56.3 months). European Society for Medical Oncology (ESMO) guidelines recommend that the removal of enlarged lymph nodes is currently part of achieving satisfactory debulking, but total lymphadenectomy should not be considered a standard procedure until clinical trial results are available. The steps of pelvic resection could be performed with different modalities including laparotomy, laparoscopy or robotic [16]. National Comprehensive Cancer Network (NCCN) guidelines recommend that attention be paid to the removal of suspicious or enlarged lymph nodes, and that there is no need to remove clinically diagnosed negative lymph nodes. Patients with extra pelvic tumor lesions $\le$2 cm should undergo bilateral pelvic and para-aortic lymph node dissection. Although lymph node dissection may provide some survival benefit in patients with ovarian cancer, it is associated with increased postoperative complications and mortality. Although the removal of enlarged lymph nodes can currently be done as part of satisfactory debulking, further research is warranted.

Radical neoplastic cytoreduction is a definitive procedure with resection of pelvic organs such as the rectum, sigmoid colon and pelvic peritoneum. In 1968, Hudson formally proposed a procedure in which the uterine appendages, affected intestinal tubes and all pelvic peritoneum are removed, resulting in a better prognosis for patients after surgery [17]. In recent years, the concept of holistic resection surgery has gradually developed and been perfected as ovarian cancer is a peritoneal disease with the peritoneum being both a transmission route and a barrier to limit the metastasis to retroperitoneal organs. En-bloc resection of the pelvis (EnBRP) is defined as the removal of all pelvic organs and peritoneum except the bladder. The specific surgical procedure is as follows: (1) entering the retroperitoneal space, free the ureter, ligation of pelvic funnel ligament; (2) truncation of sigmoid colon; (3) free the sigmoid colon from the sacrum by electrocoagulation and excision of the sigmoid mesentery; (4) enter the anterior sacral space; (5) free bladder peritoneum; (6) incision of the anterior vaginal wall; (7) retrograde excision of para-uterine tissues; (8) incise the posterior vaginal wall and enter the recto-vaginal space; (9) separation by electrocoagulation to remove pararectal tissue; 10 rectal or intestinal anastomosis. The goal of this procedure is to completely remove all pelvic lesions and reduce bleeding. Tozzi et al. [18] indicated that 98 patients with advanced ovarian cancer received EnBRP with all receiving satisfactory debulking with no intraoperative deaths and only two patients developing intestinal anastomosis fistula (2%). This procedure has been standardized and is safe and feasible for patients with advanced ovarian cancer. Diaphragmatic surgery and consequent pleural effusion have been reported following this procedure [19].

In 2013, NICE proposed “ultra-radical” surgery for patients with advanced ovarian cancer. Ultra-radical surgery includes diaphragmatic resection, extensive peritoneal resection, splenectomy, cholecystectomy, endometrectomy, gastrectomy, and hepatic resection. With the expansion of the scope of surgery and the extension of the operative time, postoperative complications will increase. A retrospective analysis of study data from multiple centers in NICE in 2019 found that the postoperative complications of ultra-radical tumor cytoreductive reduction were not significantly different from the standard procedure [20].

Ultra-radical tumor cytoreduction is radical surgery along with any of the following surgical procedures: extensive peritoneal resection including partial diaphragmatic resection, diaphragmatic resection and repair; resection of hepatic surface lesions and exploration of the hepatic hilar area; splenectomy and pancreatic tail resection; other intestinal tube resection, partial gastric resection, etc.; and tumor resection at the thoracic cavity, such as excision of lymph nodes with angular enlargement of the heart. After the promotion of NICE recommendations, the operation has been performed in numerous locations for patients with advanced ovarian cancer. When the classic standard surgery has difficulty in achieving satisfactory tumor reduction, ultra-radical tumor cytoreduction is the recommended treatment method. Due to the complexity of the surgical procedure, which involves the removal of multiple organs of the epigastric, hepatobiliary, pancreas and spleen, multidisciplinary teamwork is required to minimize complications. Patsner [21] laser-cauterized diaphragmatic lesions in three patients with ovarian cancer, successfully removing isolated lesions of diaphragmatic metastases.

Subsequently, the international centers carried out and reported the analysis of diaphragm resection surgery and its postoperative complications in ovarian cancer. The results of multi-center studies consistently showed that diaphragmatic resection can improve the extent of tumor reduction. Thus, diaphragmatic excision is fully feasible [22], although there are pulmonary complications such as pleural effusion, pulmonary embolism, pneumothorax and lung infection.

Patients with advanced ovarian cancer have a heavy tumor load and may require extensive radical surgery which poses a challenge for centers or surgeons who are not familiar with these procedures. Pleural effusion, malnutrition and lymphedema may lead to a decline in physical function, further limiting the recovery ability of ovarian cancer patients after surgery. In addition, many elderly patients suffer from multiple comorbidities. Therefore, in order to improve the rate of satisfactory tumor reduction and minimize surgical complications, neoadjuvant chemotherapy (NACT) came into being [35, 36, 37]. Compared with initial cytoreductive surgery, patients with NACT have low blood loss, low transfusion rates, short surgical time, low incidence of serious complications, short postoperative hospital stays, short ICU hospital stays, low bowel resection rates, low splenectomy rates, a significantly lower frequency of tumor invasion into the appendix and a low incidence of permanent colostomy [38]. A randomized controlled trial of 670 cases of primary ovarian cancer in EORTC-NCIC demonstrated the need for NACT to reduce extensive surgery, in which NACT reduced patients with metastases $>$10 cm by 37%. Therefore, the primary role of NACT may be to shrink rather than eradicate metastases, and even the use of NACT should not change the need for debulking surgery [39, 40, 41, 42].

A retrospective study conducted by the Korea National Cancer Center in 140 and 116 patients with advanced ovarian cancer who underwent primary tumor cytoreduction and NACT+ intermediate tumor cytoreduction, respectively, showed that NACT may improve patient outcomes, reduce blood loss and surgical complexity, and have a satisfactory tumor reduction rate similar to that of the primary tumor cytoreductive group, and that NACT can increase the success rate of tumor reduction surgery without affecting overall survival. However, even with the help of NACT, hyper radical resection is necessary to achieve satisfactory tumor reduction with 60 percent of patients receiving NACT still undergoing ultra-radical tumor cytoreduction [43].

In summary, a significant proportion of patients who receive NACT still require radical tumor cytoreductive or ultra-radical tumor cytoreductive surgery. While NACT may reduce surgical complexity and provide a greater chance for satisfactory tumor reduction, NACT has not completely eliminated the need for extensive surgery in ovarian cancer patients. If the goal is to achieve satisfactory tumor reduction, it is often necessary to require ultra-radical surgery [39, 41]. Target therapies as Poly (ADP-ribose) polymerase (PARP) [44] are also rising strategies for combination therapy.

With the development of three-dimensional conformal radiotherapy and intensity-modulated radiotherapy and the increase of concurrent chemoradiotherapy, radiotherapy for ovarian cancer has made new progress. Although chemotherapy has a good effect on advanced EOC, especially chemotherapy based on paclitaxel and cisplatin which has a significant short-term effect, it does not significantly improve survival [45]. The combination of radiotherapy and chemotherapy can play a synergistic anticancer role. Studies have shown [10] that secondary tumor cell reduction for platinum-sensitive patients can effectively prolong postoperative survival, but there is no clear effect on the effect of secondary surgery on drug-resistant patients. Because ovarian epithelial cancer cells are more sensitive to radiation, combinations with radiotherapy can effectively improve the therapeutic effect. Local radiotherapy can effectively relieve tumor pain, but the recurrent foci of ovarian cancer are mostly located in the abdomen and pelvis, so it is necessary to perform full abdominal radiotherapy for residual tumor to obtain the ideal therapeutic effect. The toxicity of radiotherapy is mild and well tolerated. Concurrent chemoradiotherapy for advanced ovarian cancer, especially for elderly patients, has been shown to be effective in the near term when surgery and chemotherapy are not suitable. At present, there are few studies on Biological Intensity Modulated Radiation Therapy (BIMRT) therapy [46], but it has been confirmed that BIMRT can improve the quality of life of cancer patients and is well tolerated. Dang et al. [47] reported that a 68-year-old female patient with ovarian cancer with abdominal metastasis received concurrent radiotherapy and chemotherapy with the tumor disappearing and the tumor markers of CA-125, CA19-9 and Carcinoma Embryonic Antigen (CEA) decreasing to normal levels. The patient’s symptoms and signs were significantly improved, and the survival time was prolonged. The use of Positron Emission Tomography-Computed Tomography (PET/CT) before and after treatment demonstrates its advantages combined with radiotherapy in tumor search, border demarcation and therapeutic effect evaluation [48]. Rochet et al. [49] verified IMRT total abdominal radiotherapy combined with surgery and chemotherapy in a phase I clinical trial.

The feasibility and effectiveness of IMRT in treating patients with advanced ovarian cancer suggest that IMRT is a novel therapeutic option for treating advanced EOC [46, 47, 50]. Advanced EOC has a high rate of recurrence, and consolidation therapies including total abdominal irradiation (WAR) have had limited success. Shetty et al. [51] reported a feasibility study, in which the whole abdomen (PTV) irradiation dose was 25 Gy/25 times and a single dose was 1Gy for 8 patients by using spiral tomography radiotherapy, and the PTV irradiation dose in the pelvic cavity was 45 Gy/25 times and a single dose was 1.8 Gy. The median follow-up time was 15 months. Five patients recovered and three had abdominal recurrence. These results demonstrate that total abdominal irradiation with IMRT can be sustained and accepted as consolidation therapy in patients with epithelial recurrent ovarian cancer at FIGO-III. It is feasible to use PET-CT, spiral tomography and CT techniques for radiotherapy of ovarian cancer with the clinical effect of PET-CT-guided radiotherapy being better.

The direction of ovarian cancer treatment in the future requires comprehensive treatment and immunotherapy. Immunotherapy, as an important component of comprehensive therapy, has recently gained medical attention. The prepared mouse monoclonal anti-idiotypic antibody 6B11 (Ab2) mimics antigen. Oc166-9 can bind to COC166-9 (Ab1) Mab and inhibit it in animal models. Anti-idiotypic antibodies can be induced by anti idiotypic antibody 6B11 (Ab3) and cellular immunity, so the antibody has the potential to act as an anti-idiotype. Antibody vaccine has been used in the treatment of ovarian cancer [52]. Immune cells (CIK, DC, etc.) were injected into the body for biotherapy. Currently, high immune system and combined immunotherapy with radiotherapy and chemotherapy, in addition to CRS has been utilized to treat ovaries cancer.

Hyperthermic intraperitoneal chemotherapy (HIPEC) is an innovative surgical technique for the treatment of primary and metastatic abdominal tumors, including certain gynecological cancers [53]. It uses highly concentrated, heated chemotherapy directly into the abdomen during surgery. After the tumor is surgically removed, heated chemotherapy fluid is circulated through the abdomen. HIPEC delivers chemotherapy directly to cancer cells in the abdomen, allowing higher doses of chemotherapy to be used and improving the effectiveness of treatment, as it is better absorbed by tumors and microscopic cancer cells remaining in the abdomen [54].