Selenium during pelvic radiotherapy for gynecologic cancer

Evidence label: Positive randomized signal in documented deficiency · Clinical goal: reduce radiotherapy-associated diarrhea without compromising cancer outcomes

Evidence at a glance

Population: 81 selenium-deficient patients receiving pelvic radiotherapy after surgery for cervical or endometrial cancer.
Intervention: sodium selenite 500 micrograms on radiotherapy days and 300 micrograms on non-radiotherapy days versus observation.
Result: grade 2 or worse diarrhea was reported in 20.5% versus 44.5%; longer follow-up did not show a disease-free or overall-survival difference.

What was studied

This small randomized phase III study enrolled patients whose whole-blood selenium was below 84 micrograms/L. Eleven had cervical cancer and 70 had endometrial cancer; 39 were assigned selenium and 42 observation.

Correcting selenium status was the primary objective. Diarrhea was a secondary clinical endpoint, so the symptom result is encouraging rather than definitive.

What the evidence shows

Grade 2 or worse diarrhea occurred in 20.5% of the selenium group and 44.5% of controls (P=.04). Selenium concentrations increased with supplementation.

At approximately six years, the follow-up report did not identify a statistically significant difference in disease-free or overall survival. The trial therefore does not establish selenium as an anticancer treatment.

Limits and uncertainty

The trial was small, open-label and restricted to patients with laboratory-confirmed deficiency. The unusually high, supervised regimen should not be generalized to people with normal selenium status.

The diarrhea result was secondary; replication in larger blinded trials is lacking.

Safety and practical context

This was a monitored research regimen, not a self-prescribing dose. Excess selenium can cause hair or nail changes, gastrointestinal symptoms, a garlic-like breath odor and neurologic problems. The NIH Office of Dietary Supplements lists an adult tolerable upper intake level of 400 micrograms/day from all sources.

Check laboratory status, kidney function, all supplements and the radiation plan with the oncology team before considering selenium.

Questions for the care team

Was selenium deficiency actually documented with an appropriate test?
How would the total intake from food, multivitamins and supplements be counted?
What monitoring and stop rules would be used, and what standard diarrhea prevention or treatment is available?

Sources

Literature searched: October 14, 2026 · Record appraised: October 14, 2026

Educational evidence summary, not personal medical advice. Supportive approaches should complement—not replace—appropriate cancer treatment and symptom management.