A decades-old cancer drug may allow eggs to mature in women with premature ovarian insufficiency, a condition that usually leads to infertility, a small pilot study suggests.

Three out of 10 women gave birth to healthy babies following treatment with rituximab, which was first approved in 1997 for blood cancers and sold by Roche and Biogen under the brand name Rituxan.

In premature ovarian insufficiency, the ovaries cease to function before the age of 40, with autoimmune mechanisms, genetics ‌and other factors playing a role. As reported in NEJM Evidence, the study involved 10 young women with autoimmune premature ovarian insufficiency whose bodies had mistakenly destroyed their ​ovaries’ egg-containing follicles.

They each underwent ovarian hormone stimulation both before and four to six months after treatment with rituximab, the first-approved cancer immunotherapy that also treats autoimmune conditions such as rheumatoid arthritis.

Ovarian stimulation involves daily hormone injections to encourage the ovaries to mature multiple eggs simultaneously.

Before treatment with rituximab, ⁠none of the women responded to the stimulation. After treatment, however, six of the 10 developed follicles that made it possible to retrieve eggs in response to ovarian stimulation.

“The results ​show that in some women there remains an egg reserve that can be activated when the autoimmune process is suppressed,” study leader Dr. Angelica Lindén Hirschberg of Karolinska Institutet in ⁠Sweden said in a statement.

In five of the women, the mature eggs could be frozen or fertilized. Three women later had embryos implanted, and all gave birth to healthy babies.

For safety reasons, embryo transfer took place no earlier than one year after treatment. One case of a serious side effect was reported and was linked to the hormone stimulation, not the immunotherapy, the researchers said.

The researchers called for larger studies to confirm the results ‌and prove the method is safe. Such a study is now underway, they said.