An extra boost of radiotherapy on top of normal radiotherapy and surgery could stop very early breast cancer returning, say international experts.
Mammograms can pick up DCIS
This strategy should be considered in all patients with ductal carcinoma in situ (DCIS), they recommend.
While DCIS is pre-cancerous or non-invasive, if left untreated it can spread to the surrounding breast tissue and become a threat.
The work, on 373 women aged 45 or younger, appears in Lancet Oncology.
One in every thousand women who attend for breast screening is diagnosed with DCIS.
Most women with DCIS have no symptoms at all. Some may have a lump, a discharge from the nipple or, rarely, a type of nipple rash known as Paget's disease of the breast.
Some areas of DCIS will never develop into invasive breast cancer even with no treatment. However, treatment is usually given because it is not currently possible to tell which areas will definitely develop into an invasive cancer.
Of the young women Dr Guenther Gruber and colleagues studied, a sixth were not given any radiotherapy after breast-conserving surgery, half received radiotherapy without a boost and the remaining two-fifths received radiotherapy with an extra boost.
The risk of the cancer returning was lowest with the boost radiotherapy and highest when no radiotherapy was given.
Dr Gruber, from Bern University in Switzerland, said: "These patients benefit from an additional boost dose."
Reducing the risk of the cancer returning would mean fewer women would need repeat surgery to remove more of the breast tissue or indeed the whole breast.
The same boost radiotherapy approach is already used and works in patients with invasive breast cancer.
He recommended that large randomised trials - the gold standard of testing methods - should be carried out to confirm their findings.
Professor John Toy, medical director of Cancer Research UK, said: "There is uncertainty about the best way to use radiotherapy after surgery for DCIS, which occurs mostly in women over 50.
"For the majority of women with DCIS, the trade-off between controlling the condition and the adverse effects of radiotherapy is complex.
"Cancer Research UK is funding an ongoing clinical trial called DCIS-II, comparing the use of radiotherapy and hormonal therapy after surgery for women over 50."
Dr Alexis Willett from Breakthrough Breast Cancer said: "Further clinical trials are now needed to fully establish the effects of this technique and ensure its safety.
"It is important to remember that radiotherapy may not be suitable for all women and each woman diagnosed with this very early form of breast cancer should discuss her individual treatment plan with her doctor."