A good biomarker is one that improves diagnosis or changes treatment.
Ovarian cancer is not a single disease but a constellation of distinct tumors, each demanding its own diagnostic language and therapeutic response. In 2026, Spanish oncology and pathology societies published a consensus framework to bring molecular precision into clinical practice—mapping biomarkers to histological subtypes so that the right test reaches the right patient at the right moment. The stakes are high: most women are diagnosed at advanced stages, and the difference between a BRCA-mutant high-grade serous tumor and a mucinous carcinoma is the difference between a PARP inhibitor and a misdiagnosis. This document is, at its core, an attempt to translate biological complexity into human survival.
- Ovarian cancer kills largely because it is caught late and treated as though it were one disease when it is actually five, each with distinct molecular drivers and therapeutic vulnerabilities.
- The dominance of high-grade serous carcinoma—70% of cases, nearly all carrying TP53 mutations and many with HRD deficiency—has made BRCA and HRD testing urgent clinical priorities, not optional add-ons.
- CA-125, the most widely used marker, misses up to 53% of early-stage cancers and rises in benign conditions, creating a dangerous illusion of certainty that the consensus explicitly cautions against.
- PARP inhibitors have reshaped maintenance therapy for HRD-positive patients, with trials like SOLO-1 and PRIMA demonstrating extended progression-free survival, but benefit narrows sharply in HRD-negative populations.
- Emerging targets—FRα, HER2, MMR/MSI, CCNE1—are beginning to unlock treatment options for recurrent disease, though most remain investigational and unequally accessible across health systems.
Ovarian cancer is a family of diseases wearing a single name. A high-grade serous tumor and a clear-cell carcinoma share an anatomical address but almost nothing else—not their molecular fingerprints, not their clinical behavior, not the drugs that can stop them. This biological reality is the premise of a 2026 Spanish consensus, jointly authored by the country's oncology and pathological anatomy societies, which sets out to map the biomarker landscape and give clinicians a practical guide for matching tests to patients and patients to treatments.
High-grade serous carcinoma, responsible for roughly 70 percent of epithelial ovarian cancers, is the most lethal subtype precisely because most women arrive at diagnosis already at an advanced stage. Nearly all such tumors carry TP53 mutations, and a significant proportion show homologous recombination deficiency—a failure in the cellular machinery that repairs broken DNA. Whether this deficiency arises from BRCA1 or BRCA2 mutations or from other repair genes, it makes tumors exquisitely sensitive to platinum chemotherapy and PARP inhibitors, drugs that exploit the cell's inability to fix itself. The consensus recommends HRD evaluation at diagnosis for all patients with non-mucinous high-grade disease at stages III and IV, since the result directly shapes first-line maintenance strategy.
The other subtypes demand different maps. Endometrioid and clear-cell tumors, each around 10 percent of cases, are strongly linked to endometriosis and carry mutations in genes like ARID1A and PIK3CA; loss of ARID1A may increase immunogenicity, suggesting a role for immunotherapy in selected patients. Low-grade serous carcinomas, driven by MAPK pathway mutations, resist conventional chemotherapy but may respond to targeted agents. Mucinous tumors present a diagnostic trap—many are actually metastases from the colon or stomach—requiring careful pathological review before any treatment decision is made.
CA-125 remains the most widely used serum marker, valuable for monitoring treatment response and detecting recurrence, but unreliable as a screening tool. It can be normal in up to 20 percent of ovarian cancers and elevated in entirely benign conditions. Large population studies found no mortality benefit from CA-125 screening, even combined with ultrasound. HE4 improves specificity when paired with CA-125, particularly in premenopausal women, but the consensus urges caution about expanding its role before further validation.
Germline and somatic BRCA testing has become a cornerstone of care. Roughly 13 to 15 percent of women with ovarian cancer carry germline mutations, and an additional 5 to 7 percent carry somatic ones. When a somatic mutation is identified, germline testing and genetic counseling should follow. For recurrent disease, emerging biomarkers—FRα for antibody-drug conjugates, HER2 for trastuzumab deruxtecan, MMR deficiency for immunotherapy—are beginning to open new doors, though most remain investigational and unevenly available.
The consensus is candid about its own limits: it organizes existing evidence rather than generating new data, and what is scientifically sound is not always immediately executable in every health system. Its practical message, however, is unambiguous—a good biomarker is one that changes treatment. The goal is not complexity for its own sake, but precision in service of survival.
Ovarian cancer is not one disease. It is a family of tumors, each with its own face, its own behavior, its own way of responding to treatment. A high-grade serous carcinoma looks nothing like a clear-cell tumor under the microscope, and they do not answer to the same drugs. This distinction—between one type of ovarian cancer and another—has become the foundation of modern treatment.
A new Spanish consensus, published in 2026 by the Spanish Society of Medical Oncology and the Spanish Society of Pathological Anatomy, attempts to map this landscape with precision. The document reviews the morphological and molecular characteristics of epithelial ovarian cancer and proposes practical recommendations for integrating biomarkers into diagnosis, prognosis, and treatment selection. It is, in essence, a guide for clinicians trying to match the right test to the right patient at the right moment.
High-grade serous carcinoma accounts for roughly 70 percent of epithelial ovarian cancers and is the most lethal subtype. Most women arrive at the clinic already at an advanced stage, which explains why this tumor type drives much of the mortality. Molecularly, nearly all high-grade serous tumors carry mutations in TP53, and many show defects in homologous recombination repair—a cellular mechanism that fixes broken DNA. These defects, called HRD, can arise from mutations in BRCA1 or BRCA2, or from other genes in the repair pathway like RAD51C, RAD51D, PALB2, BRIP1, and ATM. A variant called SET, with its distinctive solid and pseudoendometrioid pattern, is HRD-positive in roughly 90 percent of cases, making these tumors exquisitely sensitive to platinum chemotherapy and PARP inhibitors—drugs that exploit the cell's inability to repair its own DNA.
The other subtypes tell different stories. Endometrioid carcinomas, about 10 percent of ovarian cancers, often arise in women with endometriosis and present at earlier stages. They harbor mutations in genes like CTNNB1, PIK3CA, PTEN, KRAS, and ARID1A, genes involved in growth signaling and chromatin remodeling. Clear-cell tumors, also around 10 percent, have an even stronger link to endometriosis and frequently carry ARID1A and PIK3CA mutations early in their development. Loss of ARID1A may increase immunogenicity, opening a door to immunotherapy in selected patients. Low-grade serous carcinomas, less than 5 percent, arise from borderline tumors and carry mutations in the MAPK pathway—KRAS and BRAF—making them resistant to conventional chemotherapy but potentially vulnerable to drugs targeting that pathway. Mucinous tumors, rare at 3 to 4 percent, present a diagnostic trap: many mucinous tumors in the ovary are actually metastases from the colon or stomach. The consensus emphasizes the importance of careful pathological review, looking at size, laterality, invasion pattern, and immunohistochemical markers to distinguish primary from secondary tumors.
CA-125, the serum marker long used to track ovarian cancer, remains the most widely employed test. Its upper limit of normal is 35 U/mL, but it can be normal in up to 20 percent of ovarian cancers and elevated in benign conditions like endometriosis, pelvic inflammation, fibroids, hepatitis, and even menstruation. In advanced disease, it rises in 80 to 90 percent of cases; in early disease, only 47 percent. This is why CA-125 works well for monitoring treatment response and detecting recurrence but fails as a screening tool for the general population. Large studies like PLCO and UKCTOCS found no mortality benefit from population screening with CA-125, even combined with ultrasound. HE4, another serum marker, is less often elevated in benign conditions and improves specificity when combined with CA-125, particularly in premenopausal women. Yet the consensus is cautious: HE4 still needs validation for broader roles in long-term management.
BRCA testing—both germline and somatic—has become central to ovarian cancer care. About 13 to 15 percent of women with ovarian cancer carry germline BRCA1 or BRCA2 mutations, with lifetime ovarian cancer risks of roughly 40 percent for BRCA1 carriers and 18 percent for BRCA2 carriers. An additional 5 to 7 percent carry somatic BRCA mutations. When a somatic mutation is found, germline testing and genetic counseling should follow. The ideal sample for testing is a surgical specimen or image-guided biopsy of untreated tumor, with at least 30 percent tumor cellularity. If tissue is unavailable, cell blocks from pleural or ascitic fluid can be used if cellularity is adequate.
HRD status guides maintenance therapy in advanced disease. If HRD is present—whether detected through gene mutations or through genomic scars like loss of heterozygosity and chromosomal instability—PARP inhibitors offer clear benefit. Studies like SOLO-1, PAOLA, PRIMA, and PRIME showed that PARP inhibitors extend progression-free survival in BRCA-mutant and HRD-positive patients. Even in HRD-negative or unknown status, some PARP inhibitors like niraparib and rucaparib showed benefit, though smaller. The consensus recommends HRD evaluation at diagnosis for all patients with non-mucinous high-grade ovarian cancer at stages III and IV, since the result determines first-line maintenance strategy after platinum-based chemotherapy.
Emerging biomarkers are opening new doors for recurrent disease. FRα, the folate receptor alpha, is overexpressed in ovarian cancer and predicts response to mirvetuximabe soravtansina, an antibody-drug conjugate. HER2 positivity, detected by immunohistochemistry, may predict response to trastuzumab deruxtecan. MMR deficiency and microsatellite instability, more common in endometrioid and clear-cell tumors, correlate with immunotherapy response. CCNE1 amplification, found in about 19 percent of ovarian cancers, marks poor prognosis and possible resistance to PARP inhibitors. Cadherin-6 and TROP-2 are targets for newer antibody-drug conjugates still in development. ARID1A loss, particularly relevant in endometrioid and clear-cell tumors, suggests vulnerabilities to EZH2 and ATR inhibitors, though much of this remains investigational.
The consensus acknowledges its own limits. It organizes evidence rather than generating new data. For established markers like BRCA, HRD, CA-125, and PARP inhibitors, the evidence is robust. For emerging markers, it is often preliminary or based on small studies. Availability varies by health system; what is scientifically sound may not be immediately executable everywhere. HRD itself is not a single universal test—different platforms, algorithms, and cutoffs exist, and genomic scars reflect past repair defects, not necessarily current function.
The practical message is simple: a good biomarker is one that improves diagnosis or changes treatment. In a newly diagnosed patient with advanced non-mucinous high-grade ovarian cancer, the pathway should include careful histological classification, baseline CA-125, germline and somatic BRCA testing, HRD evaluation, and discussion of maintenance therapy after platinum response. In follow-up, CA-125 can signal recurrence but should not trigger treatment by elevation alone. For recurrent disease, newer biomarkers begin to unlock new therapeutic options. The field is growing more complex, but the goal remains constant: match the right test to the right patient, and use the answer to guide the right treatment.
Citas Notables
Ovarian cancer functions more like a family of tumors with different appearance, biological behavior, prognosis, and therapeutic sensitivity rather than a single disease.— SEOM-SEAP consensus guidelines
CA-125 can signal recurrence but should not trigger treatment by elevation alone, as initiating therapy based solely on marker rise has not demonstrated survival benefit and may worsen quality of life.— SEOM-SEAP consensus guidelines
La Conversación del Hearth Otra perspectiva de la historia
Why does it matter that ovarian cancer is not one disease but many?
Because a drug that works brilliantly for one type may do nothing for another. If you treat a high-grade serous tumor and a clear-cell tumor the same way, you're ignoring their biology. The serous tumor has a broken DNA repair system; the clear-cell tumor doesn't. One responds to PARP inhibitors, the other doesn't. Getting the type right is the first step to getting the treatment right.
So biomarkers are really about matching biology to therapy?
Exactly. A biomarker is a flag that says: this tumor has this vulnerability. BRCA mutations mean the cell can't fix its DNA properly, so it dies when you hit it with platinum or PARP inhibitors. HRD means the same thing, but detected a different way. FRα overexpression means the tumor is hungry for folate, so you can target it with a drug carrying folate receptor poison. The biomarker is the key; the drug is the lock.
The document mentions that CA-125 fails as a screening tool. Why do doctors still use it so much?
Because it works for what it's actually good at—tracking a patient you already know has cancer. If you've treated someone and their CA-125 drops, you know the treatment worked. If it rises later, recurrence may be coming. But if you use it to screen healthy women, you'll find a lot of false alarms and miss early disease anyway. The confusion is between what a test can do and what it should do.
What's the biggest gap between what the consensus recommends and what's actually available in most hospitals?
Access to molecular testing. The consensus assumes you can test for BRCA, HRD, FRα, HER2, MMR status. But in many places, that's expensive, slow, or unavailable. A scientifically perfect recommendation doesn't help if the test doesn't exist where the patient is being treated. That's the real-world limit.
Is there a biomarker that surprised you in this document?
KELIM—the speed at which CA-125 falls during early chemotherapy cycles. It's not well known, but it predicts who will respond well to platinum and who might need something different. It's a simple idea: measure the slope, not just the endpoint. But it requires serial blood draws and careful calculation, so most places don't do it. It's a tool waiting for infrastructure.
What should a patient ask their doctor about biomarkers?
Ask why the test is being done and how the result will change your treatment. If the answer is vague, push back. A good biomarker test should unlock a specific therapy or change the plan in a concrete way. If it's just information with no action attached, it may not be worth doing right now.