It’s best known as a weed-killer or a favourite weapon of murderous old ladies, but arsenic could find a new role as a mainstream treatment for leukaemia, Iranian researchers said on Wednesday.

They were so impressed with trials involving patients with a rare type of leukaemia that they have suggested it could be used as an initial treatment.

“There have been a few studies done using arsenic…but we are the first group to suggest that it is acceptable as a first-line treatment,” Dr. Ardeshir Ghavamzadeh of Tehran University of Medical Sciences said in a statement.

In a study reported at a European oncology meeting in Geneva, the researchers said arsenic was effective against acute promyeloctytic leukaemia, or APL, a cancer of the blood and bone marrow that affects myeloid blood cells.

APL, which affects 20,000 people worldwide, is most common in the elderly. It is a subtype of acute myeloid leukaemia, the most common form of adult leukaemia.

Ninety percent of 63 patients who had not been previously treated for the illness had complete remission after two courses of the arsenic treatment. More than 88 percent were still alive with a mean survival time of nearly 34 months.

“What this means is that we now have the possibility of offering APL patients a new first-line treatment that avoids conventional chemotherapy,” said Ghavamzadeh.

Arsenic compounds have been used in medicine for thousands of years, dating back to the ancient Chinese and Romans. In the 1980s, Chinese researchers first tried it in leukaemia after discovering it was an active ingredient in some traditional Chinese medicines, according to the researchers.

The poison was made famous in the 1944 film “Arsenic and Old Lace” staring Cary Grant. It was based on a stage play of the same name.