The immune system can be an important ally in the fight against cancer. A study from McGill scientists published today in Science suggests that the reverse may also be true – that abnormal inflammation triggered by the immune system may underlie the development of stomach tumours in patients with a hereditary cancer syndrome known as Peutz-Jeghers Syndrome (PJS). The findings are likely to prompt a re-thinking of how gastric tumours form in patients with this syndrome and in others with gastrointestinal cancers.