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How Tumors Can Outsmart Cancer Drugs

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Scientists have discovered that cancer cells can use the immune system in order to protect themselves against the cancer killing properties of an anti-cancer drug.

Tumors recruit large numbers of white blood cells, which form part of the body’s defense system, to shield themselves from the effects of a cancer drug called combretastatin A4P (CA4P). The drug works on a vascular level by blocking the blood vessels in tumors and causing them to die.

However, after treatment in animals, the research team found that the tumors began to release a protein called CXCL12 to take white blood cells from the bloodstream into the treated tumor where they then block the effect of the drug and encourage tumor growth. This may actually make tumors super resistant and make the cancer worse.

Doctors would have to block the receptor for CXCL12 in the white blood cells, part of the immune system, in order for the drug to have any benefit.

Professor Claire Lewis, lead scientist in the research at Sheffield University, UK, said, “We know that drugs that block blood vessels in tumors have a really damaging effect on the cancer, but this is often only short-lived and tumors start to re-grow. By expanding our research into what prompts macrophages to drive a tumor’s re-growth after therapy we should now be able to find ways of blocking their effects and making such treatments more effective."

Professor Malcolm Reed, Head of Surgical Oncology at the University of Sheffield, commented, “This exciting work provides valuable insights into the possible mechanism which may result in a cancer becoming resistant to treatment with chemotherapy. This has the potential to help develop new approaches to improve treatment for patients.”

Source: Welford, A.F. et al. TIE2-expressing macrophages limit the therapeutic efficacy of the vascular-disrupting agent combretastatin A4 phosphate in mice (2011) Journal of Clinical Investigation,doi:10.1172/JCI44562.

Joanna is a freelance health writer for The Mother magazine and Suite 101 with a column on infertility, http://infertility.suite101.com/.

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