Ovarian cancer staging determines how far the disease has spread at the time of diagnosis, and it is the single most powerful predictor of a patient’s outlook and treatment plan. The system used worldwide is maintained by the International Federation of Gynecology and Obstetrics (FIGO), which last revised its staging framework in 2014 to reflect improved understanding of the disease’s biology and spread patterns. Unlike some cancers that can be staged reliably through imaging alone, ovarian cancer staging almost always requires surgery to inspect the abdominal cavity, take tissue samples, and evaluate lymph nodes directly. That surgical emphasis makes ovarian cancer staging unusually hands-on and, for the patient, unusually consequential in shaping what happens next.
How the FIGO Staging System Is Organized
FIGO stages for ovarian cancer run from I through IV and describe a progression from disease confined to one or both ovaries all the way to distant metastasis. Stage I means the cancer is limited to the ovaries or fallopian tubes. Stage II means it has spread to other pelvic structures such as the uterus or bladder. Stage III means it has reached the abdominal lining (the peritoneum) or retroperitoneal lymph nodes. Stage IV means it has moved to distant organs or produced a malignant pleural effusion.
The 2014 revision made several meaningful changes. The system now formally groups cancers of the ovary, fallopian tube, and peritoneum together, reflecting the growing consensus that high-grade serous carcinoma, the most common subtype, frequently originates in the fallopian tube rather than the ovary itself. Stage IC was subdivided into three categories: IC1 for intraoperative surgical spill, IC2 for capsule rupture before surgery or tumor on the ovarian surface, and IC3 for malignant cells found in ascites or peritoneal washings. These distinctions matter because the circumstances of how cancer cells escape the ovary influence prognosis differently.1PubMed Central. FIGO’s staging classification for cancer of the ovary, fallopian tube, and peritoneum: abridged republication
At the other end of the spectrum, Stage III also received significant restructuring. Previously, retroperitoneal lymph node involvement alone placed a patient at Stage IIIC, the same category as extensive peritoneal disease. The revised system created a new Stage IIIA1 for lymph-node-only spread, subdivided by node size: IIIA1(i) for nodes 10 mm or smaller and IIIA1(ii) for nodes larger than 10 mm. This change recognized that women whose cancer has reached lymph nodes but not the peritoneal surface tend to do better than those with widespread abdominal deposits.2PubMed. Cancer of the ovary, fallopian tube, and peritoneum
Why Staging Is Primarily Surgical
In most solid cancers, imaging scans can provide a reasonably accurate stage before treatment begins. Ovarian cancer is different. The disease characteristically spreads by shedding cells across the peritoneal surface in tiny implants that CT scans and even PET scans can miss when they are only a few millimeters across. As a result, accurate staging depends on a surgeon opening the abdomen, systematically inspecting the peritoneal surfaces, collecting fluid for cell analysis, taking biopsies from the peritoneum and omentum, and removing lymph nodes for microscopic examination.
A standard staging procedure for apparently early-stage disease includes removal of the uterus and both ovaries and fallopian tubes, an omentectomy, systematic pelvic and para-aortic lymph node dissection, and random peritoneal biopsies from multiple sites.3PubMed Central. Different Surgical Approaches for Early-Stage Ovarian Cancer Staging. A Large Monocentric Experience For younger patients with Stage IA disease who want to preserve fertility, a more conservative approach that spares the uterus and the unaffected ovary can be considered, though the rest of the staging procedure still needs to happen.
This thoroughness exists for good reason. In early-stage disease, lymph node metastases are present in roughly one out of seven patients, even when imaging appears normal. A review found the average rate of lymph node involvement in clinical Stage I–II disease was about 14%, with higher-grade tumors carrying rates as high as 20%.4PubMed. Lymph node metastasis in stages I and II ovarian cancer: a review Without thorough surgical staging, these patients would be understaged and potentially undertreated.
Laparoscopic Versus Open Surgery for Staging
Traditionally, staging required a large midline abdominal incision (laparotomy). Over the past two decades, laparoscopic staging has emerged as an alternative for patients with apparent early-stage disease. Published comparisons show that laparoscopic staging takes somewhat longer in the operating room but achieves surgical assessment comparable to open surgery, with similar rates of adequate lymph node harvesting and peritoneal sampling.5PubMed Central. Laparoscopic Surgical Staging of Early Ovarian Cancer
A study comparing the two approaches for apparent early ovarian cancer found equivalent accuracy, similar long-term survival, and significantly shorter hospital stays with laparoscopy.6PubMed Central. Comparison of Laparoscopy and Laparotomy in Surgical Staging of Apparent Early Ovarian Cancer Laparoscopy is not appropriate for advanced disease, where bulky tumors require open debulking surgery. But for the subset of patients whose cancer appears confined to the pelvis on imaging, it offers a less invasive path to proper staging.
The Role of Imaging
Imaging cannot replace surgery for definitive staging, but it plays a critical role in treatment planning, particularly in advanced disease. CT, MRI, and PET/CT each have strengths for evaluating how widely the cancer has spread across the peritoneal surfaces and whether distant organs are involved. A systematic review and meta-analysis found that MRI and PET/CT both outperformed standard CT for detecting peritoneal metastases on a per-patient basis, while all three modalities performed comparably when evaluated lesion by lesion.7PubMed Central. Imaging of Peritoneal Metastases in Ovarian Cancer Using MDCT, MRI, and FDG PET/CT: A Systematic Review and Meta-Analysis
Another study comparing all three modalities found high and statistically comparable overall accuracy, with sensitivity for peritoneal disease reaching the mid-to-high 90s across all three scans.8Clinical Nuclear Medicine. Peritoneal Carcinomatosis in Primary Ovarian Cancer Staging: Comparison Between MDCT, MRI, and 18F-FDG PET/CT In practice, CT is the most widely available and commonly used first-line scan. MRI is favored for characterizing pelvic masses in detail, while PET/CT adds value when distant spread is suspected or when the treatment team needs to decide whether surgery or chemotherapy should come first.
Stage IV and Distant Metastasis
Stage IV ovarian cancer is defined by the presence of disease beyond the abdominal cavity. A landmark study of Stage IV patients found that the most common sites defining Stage IV disease were malignant pleural effusion (fluid around the lungs containing cancer cells) and liver metastases, followed by distant lymph nodes and lung involvement.9PubMed. Natural history of stage IV epithelial ovarian cancer The 2014 FIGO revision further subdivided Stage IV into IVA (malignant pleural effusion only) and IVB (metastases to the liver, spleen, distant lymph nodes, or other extra-abdominal sites), acknowledging that these presentations carry different prognoses.
An important nuance: the liver surface can be coated with peritoneal implants, which is Stage III disease, not Stage IV. Stage IV liver involvement specifically means cancer within the liver tissue itself (parenchymal metastasis). That distinction is easy to miss on imaging and sometimes only becomes clear during surgery.
Why Histological Subtype Matters for Staging Patterns
Ovarian cancer is not a single disease. The different histological subtypes tend to present at different stages, and understanding this shapes both the staging workup and expectations for what will be found. High-grade serous carcinoma, the most common type, accounts for the vast majority of advanced-stage cases. One study found that high-grade serous tumors made up about 88% of Stage III/IV cancers but only about 36% of Stage I/II cancers.10International Journal of Gynecological Pathology. Differences in Tumor Type in Low-stage Versus High-stage Ovarian Carcinomas In contrast, clear cell, endometrioid, and mucinous cancers are diagnosed at an early stage far more often. Clear cell and endometrioid carcinomas each made up roughly a quarter of low-stage tumors but less than 5% of high-stage tumors in the same study.
This distribution has practical consequences. A mucinous carcinoma found on imaging is more likely to be early-stage, but it still needs full surgical staging. In a study of patients with apparently early-stage mucinous ovarian carcinoma, about 9% were upstaged after complete surgical assessment. Among those with apparent Stage IA disease, none were upstaged, but among patients with other apparent early substages, the upstaging rate reached nearly 13%. Bilateral ovarian involvement and a history of prior mucinous ovarian tumors were independent risk factors for being upstaged.11PubMed Central. Surgical staging of apparent early-stage ovarian mucinous carcinoma
The Problem of Capsule Rupture in Early-Stage Disease
One staging detail that concerns many patients is capsule rupture, meaning the tumor’s outer surface breaks during surgery and spills cells into the pelvic cavity. The FIGO system accounts for this: surgical spill bumps an otherwise Stage IA tumor to IC1, while rupture that occurred before surgery moves it to IC2. The clinical question is whether this reclassification reflects a genuine change in risk.
A large study found that intraoperative capsule rupture was associated with worse outcomes, with the effect varying by tumor type. The impact was largest for clear cell carcinoma, where rupture roughly doubled the risk of cancer-related death.12PubMed Central. Intraoperative Capsule Rupture, Postoperative Chemotherapy, and Survival of Women With Stage I Epithelial Ovarian Cancer A more recent study focused on early-stage disease found that rupture was an independent prognostic factor particularly in patients with high-grade tumors.13PubMed. Prognostic impact of intraoperative rupture in early-stage epithelial ovarian cancer: an ancillary study of GORILLA-3002
The reassuring news is that adjuvant chemotherapy appears to offset much of that increased risk. A multi-institutional study found that when patients who experienced intraoperative rupture received chemotherapy, the increased recurrence risk associated with rupture was no longer observed.14PubMed Central. Impact of incomplete surgery and adjuvant chemotherapy for the intraoperative rupture of capsulated stage I epithelial ovarian cancer This is why accurate substaging of IC disease matters: it directly informs the decision about whether chemotherapy is warranted after surgery for early-stage cancer.
Residual Disease After Surgery
For patients with advanced ovarian cancer (Stage III or IV), the amount of tumor left behind after debulking surgery is one of the strongest predictors of survival. Surgeons aim for what is called complete cytoreduction, meaning no visible residual disease. When that goal cannot be achieved, even small amounts of leftover tumor carry consequences. A meta-analysis found that compared to patients with no visible residual disease, those left with up to 1 cm of tumor had about 75% higher risk of disease progression and death, while those with more than 1 cm of residual tumor had roughly double the risk.15PubMed Central. The impact of varying levels of residual disease following cytoreductive surgery on survival outcomes in patients with ovarian cancer: a meta-analysis
These findings held regardless of disease stage, type of surgery, or adjuvant chemotherapy regimen. A nationwide Norwegian study confirmed that any macroscopic residual disease, even deposits well under 1 cm, was associated with roughly two and a half times higher mortality compared to complete resection. The association was consistent across different histological subtypes.16British Journal of Cancer. Ovarian cancer survival by residual disease following cytoreductive surgery: a nationwide study in Norway For low-grade serous carcinoma specifically, a meta-analysis found that macroscopic residual disease after primary surgery was associated with roughly three times the risk of death compared to minimal residual disease.17PubMed. Survival impact of residual disease and timing of surgery in the management of advanced-stage low grade serous ovarian cancer
Residual disease is not technically part of the FIGO stage itself, but it functions as a critical companion variable. Two patients can have the same stage yet face dramatically different outcomes depending on how completely their tumor was removed.
Neoadjuvant Chemotherapy and Pathologic Response Scoring
Not every patient with advanced ovarian cancer goes straight to surgery. When the tumor burden is so extensive that complete resection seems unlikely, oncologists often give three to four cycles of chemotherapy first, followed by interval debulking surgery. This approach, called neoadjuvant chemotherapy, has become increasingly common for Stage IIIC and IV disease.
After neoadjuvant chemotherapy, how the tumor responded to the drugs is assessed in the tissue removed at surgery. A system called the Chemotherapy Response Score (CRS) grades this on a three-tier scale, with CRS 3 representing a complete or near-complete pathologic response (minimal or no residual tumor in the omentum). In the validation cohort for this scoring system, patients with a CRS 3 response had dramatically better progression-free survival compared to those with lower scores, and CRS 3 predicted sensitivity to platinum-based chemotherapy with high accuracy.18PubMed. Chemotherapy Response Score: Development and Validation of a System to Quantify Histopathologic Response to Neoadjuvant Chemotherapy in Tubo-Ovarian High-Grade Serous Carcinoma The CRS is gradually being adopted as a standardized way to capture treatment response that complements staging information.
Biomarkers in the Staging Landscape
Blood-based biomarkers do not determine the FIGO stage, but they contribute to the clinical picture surrounding staging. CA-125 is the most widely used serum marker. Its levels tend to correlate with the extent of disease: patients with higher clinical stages, poorly differentiated tumors, ascites, or metastases have significantly higher CA-125, HE4, and CEA levels than those with lower-stage, better-differentiated tumors.19PubMed Central. Correlation of Molecular Tumor Markers CA125, HE4, and CEA with the Development and Progression of Epithelial Ovarian Cancer After treatment, declining marker levels reflect the tumor’s response.
Despite early enthusiasm about combining HE4 with CA-125 in algorithms like ROMA (Risk of Ovarian Malignancy Algorithm) to improve diagnostic accuracy, prospective validation has been less encouraging. One study found that ROMA and HE4 did not significantly outperform CA-125 alone for detecting malignancy overall, though ROMA performed better specifically for epithelial ovarian cancer versus benign disease.20PubMed Central. HE4 and CA125 as a diagnostic test in ovarian cancer: prospective validation of the Risk of Ovarian Malignancy Algorithm Biomarkers remain useful for monitoring rather than staging, and a rising CA-125 after treatment often signals recurrence before imaging can detect it.
Sentinel Lymph Node Mapping
Full pelvic and para-aortic lymph node dissection is part of standard staging but carries risks including lymphedema, longer operative time, and surgical complications. Researchers have been exploring whether sentinel lymph node mapping, widely used in breast cancer and melanoma, could reduce the need for complete dissection in ovarian cancer. The concept is the same: inject a tracer near the tumor, identify the first nodes that drain it, and examine those nodes intensively.
A prospective trial (MELISA) evaluating sentinel node mapping in early-stage ovarian cancer reported a sensitivity of 100% with a false-negative rate of 0%, though the sample was small. Ultrastaging of the sentinel nodes identified a range of findings from macrometastases to isolated tumor cells that standard pathology might have missed.21PubMed. Mapping sentinel lymph nodes in early-stage ovarian cancer (MELISA) trial – a further step towards lymphadenectomy replacement A broader review of sentinel node research in ovarian cancer concluded that while detection rates and accuracy look promising, larger collaborative trials are still needed before the technique can replace systematic lymphadenectomy in routine practice.22PubMed Central. Where are we going with sentinel nodes mapping in ovarian cancer?
When the Ovarian Mass Is Not Primary Ovarian Cancer
A wrinkle in staging that clinicians watch for is the possibility that an ovarian mass is actually a metastasis from a cancer somewhere else. Krukenberg tumors, for example, are ovarian metastases classically originating from a gastric or colorectal primary. Distinguishing a Krukenberg tumor from a primary ovarian malignancy on imaging is difficult but essential because the staging system, prognosis, and treatment all change depending on where the cancer started.23PubMed. Krukenberg Tumors: Update on Imaging and Clinical Features
On CT, Krukenberg tumors can appear as large, lobulated, multicystic masses that look identical to primary ovarian cancer.24PubMed. Computed tomography of Krukenberg tumors One of the most useful imaging clues is bilaterality: secondary tumors of the ovary are more likely to involve both ovaries compared to primary cancers, which often begin on one side.25PubMed. Imaging in secondary tumors of the ovary When there is any suspicion that an ovarian mass could be metastatic, the workup typically expands to include upper and lower GI evaluation before the staging framework for ovarian cancer is applied.
Non-Epithelial Ovarian Cancers
The majority of ovarian cancer staging literature focuses on epithelial tumors, which account for about 90% of ovarian malignancies. But the remaining 10%, including sex cord-stromal tumors and germ cell tumors, follow different biological rules. Granulosa cell tumors, the most common sex cord-stromal subtype, tend to be diagnosed at an early stage and grow slowly, but they carry a risk of late recurrence years or even decades after initial treatment. Surgery remains the primary treatment, and stage is the most important prognostic factor. Younger patients with Stage I disease can often be treated with removal of only the affected ovary and tube, preserving fertility, while postmenopausal patients or those with advanced disease undergo more extensive surgery.
How BRCA Mutations Interact With Staging
Genetic factors are not part of the FIGO staging system, but they influence prognosis in ways that increasingly factor into treatment decisions. Women with BRCA1 or BRCA2 mutations who develop ovarian cancer tend to have high-grade serous tumors that present at an advanced stage. Paradoxically, within the first few years after diagnosis, carriers of these mutations appear to fare better than non-carriers at the same stage, likely because BRCA-mutated tumors are more sensitive to platinum chemotherapy. In a large study, the three-year survival advantage for BRCA mutation carriers was significant (adjusted hazard ratio of 0.68). However, this early advantage faded over time, and by 10 years the survival curves converged.26PubMed Central. Long-Term Ovarian Cancer Survival Associated With Mutation in BRCA1 or BRCA2
The introduction of PARP inhibitors, which exploit the DNA repair deficiency in BRCA-mutated tumors, has further changed the landscape. While PARP inhibitors do not alter the stage itself, they represent a targeted therapy option available specifically to patients with certain molecular profiles, adding another layer to how staging information is used in treatment planning. This is one reason genetic testing has become standard practice in newly diagnosed ovarian cancer, regardless of stage or family history.