An Italian study has suggested that surgery may increase the risk of cancer recurring. The researchers studied 1173 women who underwent mastectomy, but no other treatment, at the Milan Cancer Institute between 1964 and 1980. 368 women had a relapse, and pre-menopausal women were much more likely to experience a relapse within 10 months of the surgery. Node negative tumours were not affected, and size of tumour seemed unimportant.
They concluded that surgery is generally beneficial and can cure some patients. But they suggest that for some women it may change the conditions and microscopic clusters of tumour cells and encourage them to grow and develop their own blood supply. Drugs that restricted tumour blood supply might help. (Dr Romano Demicheli - Breast Cancer Research).