The finding is based on data from the Hermine trial, an observational study involving 340 women with advanced HER2-positive breast cancer.
Herceptin is the only HER2-targeted therapy proven to extend lives in both early and advanced stages of the disease.
The researchers found that the average survival rate for those who continued to take the drug after the disease progressed was 27.8 months, as compared to the 16.8 months for patients who gave it up.
This means that women with the disease are three times more likely to be alive two years later compared to those who do not take the treatment.
Dr Murray Brunt, clinical oncologist at the University Hospital of North Staffordshire NHS Trust, said that the data provides evidence that Herceptin therapy should be continued beyond progression.
"This data is very welcome and provides evidence supporting the continuation of Herceptin therapy beyond disease progression for women with this particularly aggressive form of breast cancer," the Daily Mail quoted him, as saying.
"It appears that maintaining Herceptin therapy alongside chemotherapy to provide continuous suppression of HER2 may enhance the effectiveness of chemotherapy, and help keep the cancer under control for longer," he added.
Herceptin works by binding to the part of the tumour essential for growth, preventing cell division, thus causing the tumour to stop growing or even shrink.
The study was released at the European Cancer Congress in Barcelona.
Specialists believe that Herceptin therapy is the most important development in breast cancer treatment for 25 years.