London, April 10 (IANS): A tumour becomes resistant to drugs over time by learning to steal normal blood vessels from surrounding tissue, called vessel co-option, and by angiogenesis, finds a new study.

Angiogenesis -- the process of new blood vessel growth -- is important for cancers to grow. Although several anti-angiogenic drugs have been developed to combat it, cancer cells often become resistant to these drugs.

The results showed that blocking both vessel co-option and angiogenesis could help in cancer treatment.

Tumours that respond to treatment initially, rely mainly on growing their own blood vessels, but develop resistance to treatment by actively stealing the normal pre-existing blood vessels of the liver instead.

The cancer cells increase their ability to move when they co-opt vessels.

Thus, targeting cancer cell movement might be used to block vessel co-option, the researchers explained in the paper published in the Journal of the National Cancer Institute.

"Our study is the first to show that cancers can adapt to treatment by actively co-opting blood vessels from nearby tissues as a mechanism of drug resistance," said one of the researchers Andrew Reynolds, from the Institute of Cancer Research in London.

For the study, the team used mice to examine how a type of liver cancer called hepatocellular carcinoma can become resistant to an anti-angiogenic drug called sorafenib.

The study may have implications not only for the treatment of liver cancer, but also for other cancer types including metastatic breast cancer and metastatic bowel cancer. 

"In the future, we hope our results will lead to the development of new drug types that target vessel co-option. We believe that drugs, which are designed to target vessel co-option could be particularly effective when used alongside existing therapies that block new blood vessel growth," Reynolds noted.