SOLO-2: What the Ovarian Cancer Trial Found

What "maintenance" means here

Ovarian cancer that comes back is usually treated with another round of platinum chemotherapy. If the cancer responds, treatment stops and everyone waits.

Maintenance therapy is what fills that gap. It is a drug taken during the quiet period, with the aim of holding the cancer back rather than shrinking a tumor that is already there.

SOLO2 tested whether olaparib could do that job, in one specific group of women.

The group, defined narrowly

Every participant had a mutation in BRCA1 or BRCA2. Those genes normally repair broken DNA, and when one is faulty the cell leans harder on a backup repair pathway.

Olaparib is a PARP inhibitor. PARP is an enzyme in that backup pathway. Block it in a cell that has already lost BRCA repair, and the cell runs out of ways to fix its own DNA.

That is why the trial screened for BRCA status before enrolling anyone. Our page on biomarker testing covers how these tests work and what they change.

Participants also had to be platinum-sensitive, meaning their cancer had responded to platinum chemotherapy before, and to have had at least two previous lines of chemotherapy. Tumors were high-grade serous or high-grade endometrioid, including primary peritoneal and fallopian tube cancer.

The design

SOLO2, also called ENGOT-Ov21, was an international, double-blind, randomized, placebo-controlled phase 3 trial.

Between September 2013 and November 2014 it enrolled 295 eligible women. They were assigned two to one: 196 to olaparib and 99 to matching placebo tablets. The olaparib dose was 300 mg, given as two 150 mg tablets, twice a day. Those were the trial tablets. Check your own bottle for what you should be taking.

That was the study schedule. People taking olaparib should follow their own prescription, which the team adjusts around blood counts.

Double-blind means neither the women nor their doctors knew which tablets were which. Randomization was balanced for how completely the cancer had responded to previous platinum chemotherapy and for how long the platinum-free interval had lasted.

The primary endpoint was progression-free survival, assessed by the investigators.

What it found

Median progression-free survival was 19.1 months with olaparib, with a 95% confidence interval of 16.3 to 25.7 months. With placebo it was 5.5 months, with an interval of 5.2 to 5.8 months.

The hazard ratio was 0.30, with a 95% confidence interval of 0.22 to 0.41 and a p-value below 0.0001.

A hazard ratio of 0.30 means that, over the period measured, the rate of progression events in the olaparib group was about 30% of the rate in the placebo group. It is one of the larger effects reported in ovarian cancer maintenance.

The cost of staying on treatment

Maintenance therapy is different from a course of chemotherapy in one important way. It goes on and on, so side effects have to be livable rather than survivable.

The most common severe side effects, graded 3 or worse, were anemia in 38 of 195 women on olaparib, which is 19%, against 2% on placebo. Fatigue or weakness affected 4% against 2%, and neutropenia 5% against 4%.

Anemia at that rate is the number to hold on to. It means roughly one in five women on olaparib needed their low red blood cell count treated, in a trial where the whole point was feeling well enough to continue.

When to get checked

Ovarian cancer is not screened for in the general population, and NCI is direct that it may cause no early signs at all. When symptoms do appear, the cancer is often already advanced.

NCI lists these as reasons to see a doctor, particularly if they persist or worsen rather than passing:

• Pain, swelling, or a feeling of pressure in the abdomen or pelvis.
• A sudden or frequent urge to urinate.
• A lump in the pelvic area.
• Gas, bloating, or constipation.

The point is duration, not drama. These are ordinary complaints, and the signal is that they do not go away on their own.

A separate route to earlier attention is family history. A known BRCA1 or BRCA2 mutation in the family, or a pattern of breast and ovarian cancer across relatives, is a reason to ask about genetic counseling before any symptoms appear. Our overview of ovarian cancer covers what happens next.

The wider picture

About 21,010 new ovarian cancers and 12,450 deaths are projected for the United States in 2026. Those are American Cancer Society estimates, carried on SEER's stat facts page. Five-year relative survival across all stages was 52.0% for people diagnosed from 2016 through 2022.

The stage distribution shows the problem. Only 22% are found while still confined to the ovary, where five-year relative survival is 91.9%. Fifty-four percent are found after distant spread, at 31.5%.

Those are population averages spanning years and treatments. They are not a forecast for any individual.

What this does not mean

SOLO2 measured progression-free survival, not overall survival. Delaying the moment a scan shows growth is a real benefit, and it is not the same as living longer. That question needed longer follow-up than the 2017 report contained.

The trial also says nothing about ovarian cancer without a BRCA1 or BRCA2 mutation, or about cancer that did not respond to platinum chemotherapy. Both were excluded by design.

And a 19.1-month median describes the midpoint of a spread. Some women in that trial had far longer, and some had far less. A median is a property of a group, not a promise to a person.

Sources

• Pujade-Lauraine E et al., Olaparib tablets as maintenance therapy in platinum-sensitive relapsed ovarian cancer with a BRCA1/2 mutation (SOLO2/ENGOT-Ov21), Lancet Oncol 2017 (NCBI E-utilities record)
• ClinicalTrials.gov record for NCT01874353 (SOLO2/ENGOT-Ov21)
• NCI PDQ: Ovarian Epithelial, Fallopian Tube, and Primary Peritoneal Cancer Treatment (Patient Version)
• NCI SEER Cancer Stat Facts: Ovarian Cancer

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

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