SOLO-1: What the Ovarian Cancer Trial Found

The problem SOLO-1 was built around

Most women with newly diagnosed advanced ovarian cancer relapse within three years of surgery and platinum chemotherapy. That was the plain statement the trial opened with.

Olaparib had already shown it could help after a relapse. Nobody knew whether giving it straight after first-line chemotherapy, before any relapse, would change anything.

What a PARP inhibitor does

Olaparib blocks PARP, an enzyme cells use to patch single-strand breaks in DNA.

Cells with a working BRCA1 or BRCA2 gene have a second repair route and cope. Cells that have lost BRCA function do not. Block PARP in a BRCA-mutated cancer cell and the damage accumulates until the cell dies. Healthy cells with intact BRCA carry on.

That is why the trial only enrolled women whose tumors carried a BRCA mutation. Our page on what a PARP inhibitor means goes further into the mechanism.

Who took part

SOLO-1 ran across 118 centers in 15 countries and randomly assigned 391 women, two to olaparib for every one to placebo: 260 and 131.

All had newly diagnosed advanced disease — FIGO stage III or IV high-grade serous or endometrioid cancer of the ovary, fallopian tube, or peritoneum — and a BRCA1 or BRCA2 mutation. Of the 391, 388 had an inherited mutation and 2 had one found only in the tumor. All had responded fully or partly to platinum chemotherapy. Everyone was fully active or nearly so.

Treatment was olaparib tablets, 300 mg twice a day, or matching placebo, for up to two years. Neither the women nor their doctors knew which they were taking. The trial gave everyone the same amount. Yours is set by your own team.

This describes the study. Your own prescription is what to follow if olaparib is part of your treatment.

What it found

The main measure was time without the cancer growing.

After a median 41 months of follow-up, the risk of the disease progressing or the woman dying was 70% lower with olaparib. The hazard ratio was 0.30, with a confidence interval of 0.23 to 0.41. At three years, an estimated 60% of women on olaparib were alive with no progression, against 27% on placebo.

A later analysis, published in 2021 with a median follow-up close to five years, put median progression-free survival at 56.0 months with olaparib and 13.8 months with placebo. Women on olaparib took it for a median of 24.6 months, essentially the full two years allowed.

What it cost

The most common severe side effects in the five-year report were anemia, in 22% of the olaparib group against 2% on placebo, and low neutrophil counts, in 8% against 5%. Serious adverse events occurred in 21% of the olaparib group and 13% of the placebo group.

The current prescribing information adds warnings that a two-year trial cannot fully capture. Myelodysplastic syndrome or acute myeloid leukemia — cancers of the bone marrow — occurred in about 1.2% of people exposed to olaparib across its indications, and the label states most of those cases were fatal. It instructs blood-count monitoring at the start and monthly thereafter. Pneumonitis occurred in 1.0%. The label also names venous blood clots and liver injury. Our page on living with a PARP inhibitor covers the day-to-day side.

Where it left practice

Olaparib is now approved in the United States as maintenance treatment for adults with BRCA-mutated advanced ovarian, fallopian tube, or primary peritoneal cancer who responded fully or partly to first-line platinum chemotherapy, with the mutation confirmed by an approved companion test.

The label carries two further ovarian indications: with bevacizumab for advanced disease that is homologous recombination deficiency positive, and as maintenance after platinum chemotherapy for recurrent BRCA-mutated disease.

That companion-test requirement is the reason BRCA testing is now done routinely at diagnosis rather than years later.

The numbers behind the urgency

The 21,010 new US ovarian cancer diagnoses and 12,450 deaths expected in 2026 come from American Cancer Society projections, republished by SEER. Five-year relative survival across all stages, for cases diagnosed in 2016 through 2022, is 52.0%.

The stage split explains the rest. Localized disease carries 91.9% five-year relative survival, regional 70.1%, distant 31.5%. But only 22% are found while localized, and 54% are already distant. There is no screening test for ovarian cancer in women at average risk.

These are group figures from past years. They do not describe any one person.

What this trial cannot tell you

• It applies to women with a BRCA1 or BRCA2 mutation. It says nothing about women without one.
• Overall survival was not mature at the primary report. The headline result is about delaying progression.
• Maintenance stopped at two years by protocol. The trial cannot describe what longer treatment would do.
• Everyone enrolled had already responded to platinum chemotherapy and was well enough to be nearly fully active.
• Rare long-term harms such as marrow cancers show up in label-wide safety data, not in a single trial of 391 people.

When to get checked

Ovarian cancer often causes nothing early, and when symptoms appear the disease is often already advanced. NCI lists these:

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

NCI's rule for acting on them is the useful part: if they get worse, or do not go away on their own, check with a doctor. What makes these symptoms worth raising is that they are new for you and keep happening, rather than that they are severe. Our page on BRCA gene changes covers who should consider genetic testing.

Sources

• Moore K et al., Maintenance Olaparib in Patients with Newly Diagnosed Advanced Ovarian Cancer, N Engl J Med 2018 — https://pubmed.ncbi.nlm.nih.gov/30345884/
• Banerjee S et al., Maintenance olaparib in newly diagnosed advanced ovarian cancer with a BRCA mutation (SOLO1/GOG 3004): 5-year follow-up, Lancet Oncology 2021 — https://pubmed.ncbi.nlm.nih.gov/34715071/
• ClinicalTrials.gov v2 API record, NCT01844986 — https://clinicaltrials.gov/api/v2/studies/NCT01844986
• DailyMed, LYNPARZA (olaparib) prescribing information — https://dailymed.nlm.nih.gov/dailymed/services/v2/spls/741ff3e3-dc1a-45a6-84e5-2481b27131aa.xml
• NCI PDQ, Ovarian Epithelial, Fallopian Tube, and Primary Peritoneal Cancers Treatment (Patient Version) — https://www.cancer.gov/types/ovarian/patient/ovarian-epithelial-treatment-pdq
• SEER Cancer Stat Facts, Ovarian Cancer — https://seer.cancer.gov/statfacts/html/ovary.html

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.

The National Cancer Information Foundation publishes Cancer Explained. This page is for learning. It is not medical advice and does not suggest a test or treatment.

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