Up to one-fifth of cancer patients use marijuana to mitigate the symptoms of battling their disease, according to a new survey and study of a cancer center in Seattle.

The numbers may show that marijuana usage to comfort cancer patients is on the rise in the 29 states that have medicinal cannabis laws on the books, the authors conclude in their study in the Wiley journal Cancer. But the actual benefits have yet to be truly studied and proven, they add.

“Despite the limited evidence for a medical role for cannabis in oncology, our data suggest that cannabis may be currently used frequently in this setting,” they write.

The survey was conducted over a total of six weeks between 2015 and 2016 at the Seattle Cancer Care Alliance. The institution treats patients from a wide geographic and demographic span, from Alaska, to Montana, Wyoming, Idaho and Oregon, in addition to Washington.

A total of 926 patients answered questions about their recent usage of marijuana. (Although that total represented only about a third of the more than 2,700 people approached agreed to take the survey).

Twenty-one percent said they had used marijuana within the last month.

Urine samples verified the survey’s conclusions. Fourteen percent tested positive for recent cannabis use, roughly equivalent to the 18 percent of patients who reported using marijuana in the week prior. (The urinalysis was performed through both the enzyme multiplied immunoassay technique, and the use of gas chromatography-mass spectrometry).

Of the 200-plus users, an equal proportion reported smoking or ingesting marijuana edibles (about 70 percent). The users had a variety of diagnoses, from solid tumor cancers to hematologic varieties of the disease.

But most (74 percent) agreed on one thing: they would want to know more about marijuana and how it could potentially help them with their illness, according to the study.

“There is a need for clinical trials evaluating the role of cannabis in symptom management and for the development of formalized education for patients and health care professional about the risks and benefits of use in this population,” the authors conclude.

The numbers may be higher in Washington state than elsewhere, since medical marijuana has been law since 1998, and the state has had a recreational usage law since 2012.

Eight states currently have recreational marijuana written into statute.