Daring Tumors: Tumor Cells Make Their Own Blood Vessels

A new study published independently by two groups shows that cancer cells can make their own blood vessels. This finding is very significant in the context of cancer treatment, as one of the methods to treat cancer is by cutting off blood vessels to the cancerous growth.

It is unclear how these results will impact the use of Avastin (Bevacizumab), an inhibitor of blood vessel formation (angiogenesis), in the treatment of cancer. We have recently reported the FDA reconsideration of Bevacizumab in breast cancer treatment.

The two independent studies were published in the recent issue of Nature. The lead of author of one of the reports was Dr Viviane Tabar at Memorial Sloan Kettering Cancer Center, New York, while the other study was from an Italian group headed by Dr Ruggero De Maria at the Oncology and Molecular Medicine, Istituto Superiore di Sanita, Rome.

Tumors are often associated with a subset of cells called stem cells. Stem cells have the potential to differentiate into different types of cells. The US group of Dr Tabar initially observed molecular markers of the cancer cells on the blood vessels associated with the tumor. Then they identified tumor cells with stem-cell-like properties and found that these cells could make blood vessels. When injected into mouse brain, these tumor cells developed blood vessels demonstrating that these progenitor cells can become both blood vessels and tumor.

The investigators used Avastin to block differentiation of tumor-stem cells into blood vessels. Avastin did not have an impact on the ability of the tumor-stem cells to differentiate into endothelial progenitors, but it blocked further maturation to endothelial cells. The authors conclude that this might explain varying results following Bevacizumab treatment in cancer.

In the study by the Italian group, the approach was totally different. They successfully killed endothelial cells generated by the tumor-stem cells resulting in significant reduction of the tumor, indicating the functional relevance of the stem-cell derived endothelial cells and raising hope for new therapeutic strategies.

Both studies were on glioblastoma, a tumor of the brain. It is possible that the same mechanism may be involved in other solid tumors, and their metastasis. However, the study resutls not rule out the significance of Avastin (Bevacizumab), rather complement this drug suggesting additional drug targets may also be considered together with Avastin in the control of aggressive tumors.

Original study can be found in the November 13 online pre-publication issue of Nature as cited below:

Wang, R. et al. Nature advance online publication doi:10.1038/nature09624 (2010).

Ricci-Vitiani, L. et al. Nature advance online publication doi:10.1038/nature09557 (2010).