Although current guidelines call for no further therapy after surgery on breast tumours one centimeter or smaller, a new study suggests that if these tumors are HER2 positive patients have an increased risk for relapse. In the largest study of its kind to date (n=1,315, including a validation set), researchers found that the five-year recurrence rate was 23 percent among patients with small HER2-positive tumours, compared with eight percent in other tumour types. Speaking at San Antonio Breast Cancer symposium 2008.