New York, April 10 (IANS) Researchers have determined that certain gastrointestinal tumours are more deadly than previously assumed.

Gastrointestinal stromal tumours (GISTs) may be malignant cancer or benign and are most commonly found in the stomach and small intestine and have significant variability in terms of size and malignant behaviour.

The finding, published online in the Journal of Gastrointestinal Surgery, showed that GISTs that are less than two cm cause 12.1 percent mortality rate for five years.

Also, up to 30 percent of patients have GISTs less than two cm in size, or slightly more than half an inch, the researchers noted.

More than 79 percent of patients have localised disease of GISTs, while for 11.4 percent the disease can spread to other regions. Previously, researchers did not expect any disease to have spread.

"While GISTs are rare, we have found that certain groups of these tumours result in a much higher mortality than expected," said Jason Sicklick, assistant professor at University of California-San Diego in US.

For the study, the team identified 378 patients with malignant GISTs of less than two cms between 2001 and 2011.​