OUTBACK: What the Cervical Cancer Trial Found

The worry OUTBACK was built around

For locally advanced cervical cancer, standard care is chemoradiation: radiation to the pelvis given at the same time as weekly cisplatin chemotherapy, which makes the radiation work better.

It cures many people. But some relapse later with cancer in distant organs, and radiation aimed at the pelvis cannot reach cells that have already left it. So oncologists reasoned that a few extra rounds of chemotherapy afterwards might mop those cells up. Many centers began doing it. Nobody had tested whether it helped.

OUTBACK tested it.

How the trial was built

Between April 2011 and June 2017, 926 patients joined at 157 hospitals in Australia, China, Canada, New Zealand, Saudi Arabia, Singapore and the United States. Of those, 919 were eligible and analyzed. The median age was 46.

Everyone had locally advanced disease, defined as FIGO 2008 stage IB1 with cancer in lymph nodes, or stage IB2, II, IIIB or IVA. The cancer type had to be squamous cell carcinoma, adenosquamous carcinoma or adenocarcinoma of the cervix.

Everyone got the same chemoradiation: cisplatin by infusion once a week for five weeks, at an amount worked out from body size, alongside 45.0 to 50.4 Gy of external beam radiation in 1.8 Gy fractions to the whole pelvis, plus brachytherapy, which places a radiation source inside the body close to the tumor.

Then 463 people were randomly assigned to four extra cycles of carboplatin and paclitaxel, and 456 were assigned to stop. The measure that counted was overall survival at five years. Our explainer on clinical trial phases covers why a phase 3 trial is built this way.

What it found

Median follow-up was 60 months. Five-year overall survival was 72% in the group given the extra chemotherapy and 71% in the group that stopped after chemoradiation.

The difference was one percentage point, and the confidence interval ran from minus 6 to plus 7. That interval crossing zero is the point: the data are consistent with a small benefit, no benefit, or a small harm. The hazard ratio was 0.90, with a range of 0.70 to 1.17, and p was 0.81.

The side effects were not ambiguous. Severe drops in neutrophils, the white cells that fight bacteria, hit 20% of the adjuvant group against 8% of the others. Severe anemia, meaning too few red blood cells, hit 18% against 8%. Serious adverse events occurred in 30% against 22%, most often infections. There were no treatment-related deaths.

The authors wrote that this chemotherapy should not be given in this setting.

Why a result of nothing is worth publishing

A trial that finds no difference is often the most useful kind. Before OUTBACK, patients were spending months in chemotherapy chairs, losing blood counts and risking infection, for a benefit that turned out not to exist.

The trial did not take a treatment away from anyone. It gave people back a season of their lives. That is the quiet value of testing what everyone already assumes, and our guide to chemotherapy explains what those cycles ask of a body.

Where cervical cancer stands

In the United States, the American Cancer Society projects 13,490 new cervical cancer diagnoses and 4,200 deaths in 2026 — the estimate SEER displays on its cervical page. Five-year relative survival across all stages, for 2016 to 2022, is 68.8%.

Stage dominates. Localized disease, still confined to the cervix, carries 91.8% five-year relative survival. Regional disease, in nearby lymph nodes, carries 64.0%. Distant disease carries 20.5%. The locally advanced patients OUTBACK enrolled sit largely in that middle band. These are group statistics from past years and do not predict any individual course. Read more in our page on cervical cancer.

When to get checked

Screening finds cervical cell changes before symptoms exist, which is the whole point of it. Between screens, these are worth a prompt appointment:

• Bleeding between periods, after sex, or at any time after menopause
• Periods that become longer or heavier than your normal
• Pelvic pain, or pain during sex
• Vaginal discharge that changes in amount, color or smell
• After cervical cancer treatment: leg swelling, back or leg pain, or trouble urinating

What this trial cannot tell you

• Patients were unselected rather than picked for high relapse risk. A narrower high-risk group might still benefit, and OUTBACK was not designed to find out.
• It tested one regimen: four cycles of carboplatin plus paclitaxel after cisplatin chemoradiation. Other drugs, schedules and immunotherapy were not tested here.
• The trial was open-label, meaning patients and doctors knew the assignment.
• Enrollment ran from 2011 to 2017, before immune checkpoint drugs entered this setting, so it does not speak to today's newest options.
• Trial participants meet specific entry criteria, so results may not carry over to everyone with this diagnosis.

Sources

• Lancet Oncology (record via PubMed), Adjuvant chemotherapy following chemoradiotherapy for locally advanced cervical cancer (OUTBACK) — https://pubmed.ncbi.nlm.nih.gov/37080223/
• ClinicalTrials.gov, NCT01414608 (OUTBACK) — https://clinicaltrials.gov/study/NCT01414608
• SEER Cancer Stat Facts, Cervical Cancer — https://seer.cancer.gov/statfacts/html/cervix.html
• NCI PDQ, Cervical Cancer Treatment (Patient Version) — https://www.cancer.gov/types/cervical/patient/cervical-treatment-pdq
• Cancer Council Australia, Cervical cancer — https://www.cancer.org.au/cancer-information/types-of-cancer/cervical-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.

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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