LONDON — A blood test that can show if a woman has breast cancer — and at an earlier stage than is possible with current tests — has been shown to work in a trial led by a British-based scientist.

The results of the first trial, published Friday, also suggest that the method could be adapted to spot melanoma and detect prostate and ovarian cancers at the “silent” phase of the disease, when a person looks and feels normal.

Breast cancer is the most common cancer in females worldwide, with an incidence of 1.1 million new cases each year and up to 400,000 deaths. Currently, diagnosis is by triple testing — breast examination, imaging with mammography and ultrasonography, and biopsy.

There is an urgent need for a more effective way of screening for breast cancer, especially for the small but increasing number of cases in younger women, for whom mammography is less sensitive.

As well as detecting the disease, blood tests could also allow differentiation of malignant breast cancers from benign ones and help to select the best treatment.

The earlier a cancer is detected, the more chance that treatment has to be effective.The five-year survival rate can be as high as 97% if a cancer is small and has not spread. While recent cancer research has focused on faulty genes that multiply out of control, this new test focuses on detecting simultaneous and subtle changes in the spectrum of proteins in the blood stream caused when the immune system begins to fight a cancer.

The feat is reported in the Journal of Proteome Research by a professor at University College London, Jasminka Godovac-Zimmermann, who headed the group, which included scientists from the universities of Pennsylvania and Pittsburgh and the company Bio-Traces, Inc., in Herndon, Va.

“Our pilot studies show that using blood samples, breast cancer, and several other types of epithelial cancers [ovarian, prostate, and melanoma] can be detected with much better sensitivity and specificity,” Mrs. Godovac-Zimmermann said.