Researchers several years ago identified a population of cells within melanoma skin cancers that may cause resistance to chemotherapy. The researchers now say that these cells, which express the protein ABCB5, may be uniquely suited to initiate tumors and fuel their growth. Dr. Markus Frank of Harvard Medical School and his colleagues report in the January 17 Nature that antibodies against this protein can help prevent tumors from developing in animal models of the disease.

The study describes a hierarchy of cells within melanoma tumors. The capacity to self-renew and give rise to diverse cell types - the hallmarks of tissue stem cells - are concentrated in the ABCB5-positive cells, the researchers conclude. An analysis of tumors revealed greater expression of ABCB5 in more clinically advanced cases compared to less advanced cases, suggesting a link between these cells and melanoma progression.

The cancer stem cell hypothesis says that some cancers are driven by small populations of self-renewing cells. The cells have been reported in various tumor types, including brain, breast, and pancreatic tumors. Previous reports on melanoma have proposed that the proteins CD133 and CD20 may be markers of tumor stem cells.

Few studies have tested the idea that patients would benefit from the eradication of tumor stem cells. Support now comes from experiments in this study showing that antibodies against ABCB5-positive cells inhibited tumors in mice.

"This study provides validation of the hypothesis that specifically targeting cancer stem cells would inhibit tumor growth," said Dr. Frank, noting that more research is needed before the strategy could be applied to humans. Additional markers to further characterize melanoma stem cells at the clonal level are also needed because not every ABCB5-positive cell is a tumor-initiating cell.