Moves to patent the controversial animal as an 'invention' sparked a wave of protest across Europe last year by groups outraged at the prospect that Harvard University, its developers, could make money from the animal's designer cancers.
However, Merck is the first major company to show any interest in exploiting the so- called 'OncoMouse' in the five years since it went on sale in the US. The European Patent Office has yet to decide whether it can be classed as a patentable invention.
The Merck deal is a relief for Du Pont, the chemicals giant behind the OncoMouse, which has invested between pounds 6m and pounds 10m over 10 years in the project. It had hoped this and similar mouse models would open up potentially lucrative drugs markets, and help scientists studying conditions ranging from heart disease to Aids. In practice, it has become an embarrassment.
Public revulsion at the concept of an animal engineered to develop cancer, coupled with unease at attempts to patent the animal, have prompted even senior figures within the industry to brand the mouse a public-relations disaster.
Du Pont claims that the OncoMouse is useful in studies of breast, colon, prostate and lung cancer. Merck has not disclosed how much it paid Du Pont, nor the lines of research that it intends to pursue. Opponents argue that, increasingly, scientists are conducting cancer research using cells cultured in the laboratory, and that to promote animal research is a retrograde step.
The European Patent Office (EPO) is trying to decide whether a patent on the animal - granted to Harvard University in 1988 - should be revoked in Europe as 'contrary to morality'. The patent, the first granted on an animal, was given a provisional go-ahead by the EPO in 1991. This provoked objections on moral, technical and legal grounds.
Inquiries by the Independent have established that the EPO has granted Harvard a third extension - to 15 April - to respond to these objections.
The EPO allowed the controversial mouse patent after deciding its potential benefit to humanity outweighed the suffering the extra genes might cause the engineered mice. But Peter Stevenson, political and legal director of Compassion in World Farming, said: 'Our opposition argued that the benefit to humanity had been given too much weight, and the fact that it has taken so long for anyone to come forward to use the technology indicates its limited use.'
He added: 'This is a test case. If we allow genetic engineering and patenting of animals to go ahead, we are giving our blessing to a whole new episode in humanity's exploitation of animals.'