Young women who undergo mastectomies should be given drugs to restrict blood supply to cancer cells, research suggests.
Treatments could reduce the risk of recurrence
An Italian study of women operated on in the 1970s suggested the surgery may increase the risk of cancer recurring.
Italian researchers writing in Breast Cancer Research said it may fuel the growth of tiny cancer cell clusters.
Women are now given chemotherapy, cutting their risk, but experts said that extra drugs could be of benefit.
The researchers looked at 1,173 women who underwent a mastectomy, but no other treatment, while participating in breast cancer trials at Milan Cancer Institute between 1964 and 1980.
They then analysed the number of women who suffered a recurrence of breast cancer in the first four years after surgery.
The scientists also looked at whether the speed with which the cancer recurred could be linked to the women's menopausal status, the size of their original tumour or whether the cancer was confined to the breast (node-negative) or had progressed into the lymph glands (node-positive).
A total of 368 patients saw a recurrence of their cancer, either in the breast or elsewhere in their body, within four years of surgery.
The researchers found that both pre-menopausal and post-menopausal women experienced an increased risk if their tumour was node-positive.
However pre-menopausal women were much more likely to experience relapse of the disease within eight to 10 months of surgery.
Surgery did not appear to affect the risk for those women with node-negative tumours. The size of the tumour was also found not to increase their risk.
The researchers found that pre-menopausal women suffering from aggressive breast cancer, who have a mastectomy but no other treatment, were at the highest risk of recurrence.
They conclude surgery for breast cancer is generally beneficial and can cure many patients.
But they suggest that, for some women, it may change the conditions around microscopic clusters of tumour cells and encourage them to grow and develop their own blood supply.
This can accelerate local or distant (metastatic) recurrence.
Writing in Breast Cancer Research, the scientists, led by Dr Romano Demicheli, said: "The risk of early recurrence for node positive patients is dependent on menopausal status.
"For pre-menopausal node-positive patients, the abrupt increase of the first narrow peak of the recurrence risk suggests a triggering event that synchronises early risk. We suggest that this event is the surgical removal of the primary tumour."
They say women are now routinely offered chemotherapy as well as a mastectomy, so the level of recurrence seen in the study should not occur now.
But they said their findings did support the use of drugs or treatments to prevent tumours developing their own blood supplies, prior to surgery.
Dr Richard Sullivan, Head of Clinical Programmes for Cancer Research UK
agreed with the researchers' conclusions.
He said: "This is an interesting observation which has been seen in other types of cancer such as bowel.
"The study followed patients who were treated with surgery alone. Current treatment for pre-menopausal breast cancer patients involves surgery and chemotherapy, and this is known to reduce the risk of the cancer recurring.
"However, this new research suggests that recurrence could be further reduced by treating women with drugs that restrict the tumour's blood supply before surgery."