People with small-cell lung cancer, a fast-growing type of lung cancer, have for decades often been given radiation to the whole brain after their first treatment, even when no cancer is seen there. The idea is to stop the cancer from spreading to the brain later. A new trial suggests many may be able to skip it. Results presented on October 28, 2026 found that watching the brain with regular MRI scans alone led to less decline in memory and thinking, and far fewer serious side effects, with no clear difference in survival so far1.
The trial, called SWOG S1827 or MAVERICK, was presented at the International Association for the Study of Lung Cancer’s 2026 World Conference on Lung Cancer in Seoul1. A physician forum also describes it as a clinical trials session presentation linked to the ASTRO 2026 meeting, a radiation oncology conference2. The results have not yet been published in a peer-reviewed journal in the sources reviewed here.
What the trial compared
The treatment in question is called prophylactic cranial irradiation, or PCI: “prophylactic” means preventive, and “cranial” means the head3. The trial enrolled 304 patients between January 2020 and December 2025. All had small-cell lung cancer, either limited-stage (still mostly in one part of the chest) or extensive-stage (spread further), had finished their first round of treatment, and had no cancer visible in the brain on MRI1.
Patients were randomly assigned to one of two plans. One group got regular brain MRI scans only. The other got the same scans plus preventive brain radiation, given as a total dose of 25 Gy (a unit of radiation dose) split over 10 sessions1. In both groups, scans happened every three months in the first year and every six months in the second, and patients took memory and thinking tests at the same visits. These included standard tests of word recall, word fluency and attention1.
The results so far
The main measure combined two bad outcomes into one: a drop on the thinking tests, or death. Researchers call this “cognitive failure-free survival.” It is meant to capture both the harm the cancer can do and the harm the radiation can do1.
After a median follow-up of 22 months among patients still alive, the scans-only group had a 40% lower risk of thinking decline or death than the radiation group1. The benefit looked similar in limited-stage and extensive-stage patients, and whether or not patients were getting immunotherapy, a type of drug that helps the immune system attack cancer1.
- Survival: an early analysis after 128 deaths showed no clear difference between the two plans1.
- Cancer showing up in the brain: time without brain spread was not significantly different between groups, so skipping radiation did not clearly raise that risk during the follow-up1.
- Serious side effects: serious treatment-related problems occurred in 0.8% of the scans-only group and 7.9% of the radiation group1. One patient in the radiation group had a brain injury called encephalopathy, rated at the highest severity grade1.
Chad Rusthoven of the University of Colorado School of Medicine, who presented the study, said:
“These results support MRI surveillance alone as the standard of care for patients with SCLC.”
That is the investigators’ view of their own trial1.
What it does not show yet
The survival picture is not final. The last survival analysis is planned after 190 deaths, and the current one came after 1281. A finding of “no clear difference” in an early look is not the same as showing the two plans are equal.
There is also a gap between the trial’s public registry record and the presented results. The ClinicalTrials.gov entry lists overall survival as the primary outcome and an estimated enrollment of 668 people4. The conference report describes thinking decline or death as the main measure and reports 304 patients enrolled1. The sources reviewed here do not explain the difference. The registry lists the trial as active but no longer recruiting, with no results posted yet4.
Doctors’ views are still mixed. On a physician forum, one radiation oncologist from Memorial Sloan Kettering Cancer Center wrote that the standard of care for limited-stage disease remains preventive radiation, while patients can make an informed choice to decline it2. Another, from USC Keck School of Medicine, wrote that it is reasonable to use MRI surveillance but that longer follow-up is needed to see survival outcomes2.
The results also apply only to patients like those in the trial: people who had finished first treatment and had a clean brain MRI before joining1. The plan depends on getting scans every few months, which the trial built in for everyone1.
Who is behind it
The trial is sponsored by the SWOG Cancer Research Network, a cancer research group4. It was first registered in November 2019 and started in May 20204. MD Anderson Cancer Center in Houston is among the sites, with radiation oncologist Matthew Ning listed as its physician on the study3. The sources reviewed do not describe any drug company funding, which fits a trial comparing a scan schedule with radiation rather than testing a product.
How it fits a long debate
Preventive brain radiation became standard because studies done before routine MRI scanning showed it cut brain spread and improved survival1. Small-cell lung cancer has very poor outcomes, with five-year survival in the single digits, and most patients develop cancer in the brain at some point, especially in extensive-stage disease5. One earlier large trial found that preventive radiation doubled one-year survival compared with simply watching patients in extensive-stage disease, and it became the US standard for that group5.
That changed for extensive-stage disease after a Japanese trial by Takahashi and colleagues, which included 224 patients from 47 Japanese institutions. It compared preventive radiation with MRI scans every three months and found no survival benefit from radiation, even though radiation lowered brain spread5. The trial even saw a trend toward worse survival with radiation and was stopped early5. US cancer guidelines from the National Comprehensive Cancer Network then began to list either radiation or MRI surveillance as options for these patients5. A survey of radiation oncologists found that routine use of preventive radiation for extensive-stage disease fell from 72% to 43% after that trial was published5.
By 2020, radiation oncologist Kristin Higgins said in an expert panel that her field had largely stopped recommending preventive radiation in extensive-stage disease and was trying to move away from it because of its side effects. She pointed to MAVERICK as the trial that would help answer the question6. She also mentioned another trial testing a gentler form of the radiation that avoids the hippocampus, the brain area involved in forming memories6. For limited-stage disease, preventive radiation has remained more widely used, which is why MAVERICK’s inclusion of those patients drew attention2.
What to watch next
- The final survival analysis, planned after 190 deaths, which will show whether the early survival picture holds1.
- A journal publication with full details, and an explanation of how the reported design lines up with the registry record4.
- A trial in China led by Shandong Cancer Hospital and Institute, comparing preventive radiation with MRI surveillance in limited-stage patients. It aims to enroll an estimated 534 people, uses overall survival as its main measure, and was listed as recruiting with a primary completion date of April 20267.
- Guideline changes: whether cancer guideline groups shift their advice for limited-stage patients, as they did for extensive-stage patients after the Japanese trial5.
This article reports research findings and is not medical advice. Decisions about cancer treatment depend on each patient’s situation and are made with their care team.
