Low-grade serous ovarian cancer (LGSC) is one of the less common forms of ovarian cancer, and in many ways it behaves like a different disease from the high-grade serous cancer that CA125 was built around. It tends to grow slowly, to affect younger women, and — importantly — it can produce far less CA125, so the test may be falsely reassuring.

What it is and how common it is

Serous ovarian cancers are divided into two groups: high-grade and low-grade. They are not simply mild and severe versions of the same thing — they arise through different biological pathways. Low-grade serous carcinoma makes up only a small share of serous ovarian cancers, and a small percentage of ovarian cancers overall.

Some low-grade serous cancers develop from a pre-existing serous borderline tumor, a growth that sits between clearly benign and clearly cancerous. LGSC is often driven by changes in a group of genes in the MAPK pathway — such as KRAS, BRAF, or NRAS — rather than the widespread genetic damage seen in high-grade disease.

Women diagnosed with LGSC are frequently younger than the typical ovarian cancer patient, sometimes in their 30s or 40s. Because it grows slowly, it can be present for a long time before it is found, and it is often diagnosed at an advanced stage even though it is indolent.

How it behaves on a CA125 test

CA125 is most strongly associated with high-grade serous carcinoma. Low-grade serous cancer can raise CA125, but the levels are often lower and less dramatic, and the test can be normal — particularly early on. Because LGSC grows so slowly, a level that looks unremarkable at one visit may creep up only gradually over time.

The practical takeaway: a normal or only mildly elevated CA125 does not rule out low-grade serous cancer. Doctors interpret CA125 alongside imaging, symptoms, and — when the disease is being monitored — the trend in your levels rather than a single value.

Symptoms and how it’s diagnosed

The symptoms of low-grade serous cancer overlap with ovarian cancer in general and can be easy to dismiss because they build up slowly:

Persistent bloating or abdominal swelling
Pelvic or abdominal pain or pressure
Feeling full quickly or changes in appetite
Changes in bowel or bladder habits

Because CA125 is unreliable here, diagnosis usually leans on other tools. A pelvic exam and a transvaginal ultrasound are common first steps; CT or MRI scans help show how far disease has spread. LGSC often has a characteristic appearance under the microscope, sometimes with small calcium deposits called psammoma bodies. As with most ovarian cancers, a firm diagnosis generally requires a pathologist to examine tissue removed at surgery.

Treatment and outlook

Treatment is usually built around surgery to remove as much of the cancer as possible, since low-grade serous cancer tends to respond less well to standard chemotherapy than high-grade disease. That relative chemo-resistance is one of the defining challenges of this subtype.

Because LGSC is frequently hormone-receptor positive, hormonal therapies — drugs such as letrozole, anastrozole, or tamoxifen that lower or block estrogen — play an important role, sometimes as maintenance treatment after surgery. Research into targeted therapy has also focused on the MAPK pathway, and MEK inhibitors have become part of the treatment landscape for some people with recurrent disease.

The outlook reflects the cancer’s dual nature. Low-grade serous cancer is generally less aggressive than high-grade disease and can be lived with over many years, but it can also recur and is harder to eradicate with chemotherapy. Prognosis depends heavily on the stage at diagnosis and how completely the cancer can be removed with surgery.

Questions to ask your care team

Has my tumor been confirmed as low-grade serous specifically?
Was my cancer tested for hormone receptors, and could hormonal therapy help me?
Has molecular testing (for example KRAS/BRAF) been considered?
Should a gynecologic oncologist be leading my care?
How will you monitor me over time, given that CA125 may not be reliable for me?

You are not alone

Low-grade serous cancer is uncommon enough that many people have never heard of it before their diagnosis — which can feel isolating. The Cure Ovarian Cancer Foundation funds research into the subtypes standard tools overlook, and supports women and families navigating a diagnosis like this one. If this page helped you, please consider making a gift so we can reach the next person who needs it.

This page is for education and awareness and is not medical advice. Your own care team knows your situation best — please bring these questions to them.