A new therapy has been shown to shrink breast cancer tumours and, in some cases, make them disappear entirely in just 11 days.
The new treatment has been shown to destroy breast cancer tumours as large as 3cm entirely.
Presenting the findings at the European Breast Cancer Conference on 10th March, Professor Nigel Bundred, from the University of Manchester, said: "This has ground-breaking potential because it allows us to identify a group of patients who, within 11 days, have had their tumours disappear with anti-HER2 therapy alone and who potentially may not require subsequent chemotherapy.
"This offers the opportunity to tailor treatment for each individual woman."
Professor Bundred ran a clinical trial with 257 women who were newly-diagnosed with operable, HER2 positive disease.
The women were recruited between November 2010 and September 2015.
The trial had two stages. In part one, 130 women were randomised to receive either no pre-operative treatment, trastuzumab on its own, or lapatinib on its own for 11 days after diagnosis and before surgery.
The next 127 women who took part in the trial were either randomised to the control group, to receive trastuzumab only, or to try the combination treatment (a mixture of trastuzumab and lapatinib).
Women who received the combination treatment presented with the best results, as the cancer disappeared entirely in 11% of cases, and in a further 17% they were smaller than 5mm.
Even women presenting with stage two breast cancer - where the cancer had spread to their lymph nodes - responded positively to the combination treatment.
Professor Judith Bliss, lead researcher from The Institute of Cancer Research, which co-led the trial, said: "These results show that we can get an early indication of pathological response within 11 days, in the absence of chemotherapy, in these patients on combination treatment.
"Most previous trials have only looked at the pathological response after several months of treatment.
"Clearly these results need further confirmation, but I suspect the excitement from seeing the speed of disappearance of the tumours will mean that several trials will attempt to confirm these results."
Professor Fatima Cardoso, who is director of the Breast Unit at the Champalimaud Clinical Centre, said: "The results of this important trial confirm previous initial suggestions that most probably there are patients who can be treated with dualblockade (two anti-HER2 agents simultaneously) alone, without chemotherapy.
"This study proposes a simple way to identify those patients very early on, which could help spare them unnecessary chemotherapy. What is now indispensable is to confirm if these early responses translate into better or equal long-term survival."