Controversial research about the way some aggressive cancers supply themselves with blood could be a blow to possible treatments.

As a tumour enlarges, a good blood supply is the key to keeping itself alive and allowing further growth.

Until now, it was thought that a key "trick" which allowed some tumours to thrive was their ability to induce the body's natural blood vessel growth to increase the supply of nutrients and oxygen to tissues. This process is called angiogenesis.

The latest research from a team at the University of Iowa suggests that some tumours may be able to produce primitive blood channels of their own by genetically manipulating cancer cells.

If this is true, then the current crop of research drugs which interfere with angiogenesis may not be as effective in starving tumours as previously hoped.

However, the research has provoked a storm of controversy among cancer experts in the US.

The latest study, led by Dr Mary Hendrix, and presented at a biology conference in the US this week, suggested that aggressive prostate cancers could form their own "primitive microcirculatory networks".

These open channels, formed in rat and human cancers grown in the laboratory, might allow blood to pass around the tumour, supplying it with the necessary nutrients.

Purpose unknown

As yet, it is unclear whether the purpose of these channels is to carry blood, although blood was found in them, and they were growing close to normal blood vessels.

Critics of the research suggest that such channels could happen naturally as the tumour expands, by chance rather than design.

Some say that even if the primitive channels are designed to carry blood, how much they contribute to total blood flow is uncertain.

The latest drugs designed to stop the body's natural blood vessels growing to supply a tumour are aimed specifically at the type of cells found in those vessels.

These are often a more responsive target than the cancer cells themselves.

The University of Iowa researchers suggest that cancer cells are able to alter their own genetic programming - the code which makes, for example, a prostate gland cell work like a prostate gland cell.

Dr Hendrix said that the prostate cancer cells she studies were reverting to "stem cells", the cells found in an embryo which eventually adapt to form every different tissue and structure in the body.

"They would revert to an embryonic stem cell, because that's how they started," she said.

"As such, they are capable of many different functions."