Scientists suggest chokeberries could work in combination with conventional drugs to kill more cancer cells.
But the UK research is at an early stage, with experiments carried out only on cancer cells in laboratories.
Cancer Research UK says much more work is needed to test the effectiveness of berries, particularly in human trials.
Researchers from the University of Southampton and King's College Hospital, London, tested a berry extract on pancreatic cancer samples.
Pancreatic cancer is particularly hard to treat and has an average survival period of just six months after diagnosis.
The study found that when the berry extract was used, together with a conventional chemotherapy drug called gemcitabine, more cancer cells died than when the drug was used alone.
But the scientists say the chokeberry had no effect on normal body cells tested in this way.
They believe compounds known as polyphenols in the berries may reduce the number of harmful cells.
And the team previously carried out similar early work on brain cancer cells.
Henry Scowcroft, at the charity Cancer Research UK, said: "It's far too early to say from this small laboratory study whether chemicals extracted from chokeberries have any effect on pancreatic cancer in patients.
"And the findings certainly don't suggest that the berries themselves should be taken alongside conventional chemotherapy.
"But innovative approaches are urgently needed to improve treatment for people with pancreatic cancer - a disease for which there has been precious little progress over recent decades."
Chokeberries grow on the eastern side of North America in wetlands and swamp areas.
Bashir Lwaleed, a senior lecturer at Southampton University, who carried out the study, said: "We need to do more research to understand how the chemotherapy and berry work together.
"At the moment we cannot suggest people go out and buy supplements - we are still at the experimental level."
The study was funded by the Malaysian ministry of higher education and health charity Have a Chance Inc in the USA.
Wild berries native to North America may have a role in boosting cancer therapy, according to a study in the Journal of Clinical Pathology.