Some cancers can release a protein that awakens dormant cancer cells throughout the body, studies in mice suggest. The discovery could help doctors understand and prevent the spread of cancers through the body. The results provide a possible explanation for why high levels of the protein, called osteopontin, in cancer patients have already been linked to an increased risk of death. Researchers are working to develop a drug that blocks the protein as a possible tool in the battle against the disease. Most patients who die from cancer do not succumb to the initial cancer, called a primary tumour, but rather from the disease’s spread to other parts of the body. Although the importance of this process, called metastasis, is clear, there is no currently available therapy that can specifically block this sinister march throughout the body.
McAllister and her colleagues, led by the Whitehead Institute’s Robert Weinberg, co-implanted two kinds of cancer cells in mice. The first, which they termed an ‘instigator’ tumour, was made of fast-growing breast-cancer cells cultured in the lab. They also injected other cancer cells, called ‘responder’ cells, which were known to grow slowly and metastasize only rarely. They found that the presence of the instigator tumour was enough to speed development of the responder, which then spawned up to nine times as many metastatic tumours as when the instigator was absent. They found similar results when they repeated the experiment using colon cancer cells collected from cancer patients as the responder tumours. Subsequent analysis showed that the osteopontin protein is crucial for this instigator effect.