The Cancer Research Campaign says that new research into fish oil could also lead to earlier diagnosis of some cancers, including lung, stomach, pancreatic and bowel cancers which are difficult to treat and spread rapidly.
Clinical trials of the chemical eicosapentaenoic acid (EPA) are to start in autumn 1993. EPA is found in purified fish oils from fatty fish such as salmon, sardines and mackerel.
Scientists at Aston University have discovered that EPA appears to alter the unique hormone-like proteins produced by some tumours.
These proteins are thought to cause the wasting process, known as cachexia, which afflicts many cancer patients. Body tissues, especially muscle and fat, start to break down despite near-normal eating habits. In the later stages of the disease, many patients have a skeletal appearance, suffer extreme fatigue and distress and are vulnerable to infections.
Professor Mike Tisdale, who heads the Aston team, said that a treatment that prevented cachexia would improve patients' quality of life. In addition, the team has 'strong experimental evidence' that EPA shrinks tumours.
'The tumour obviously needs to take substances from other body cells to help it grow and produces the protein to break down the cells to release these substances. By blocking this process we can shrink the tumour . . . Our work so far is promising.'
Identifying the protein in the blood or urine of patients with weight loss may aid early diagnosis of cancer so that doctors can start therapy sooner, Professor Tisdale added. Weight loss is one of the first symptoms of some cancers but may be confused with other illnesses. By the time cancer is confirmed, the tumour may have spread.
Professor Gordon McVie, scientific director of the CRC, said yesterday that the research could explain the low cancer incidence among Eskimos whose diet is rich in fish. He warned that a drug based on fish oil to treat cancer was unlikely before 1995, but described the findings as 'highly important', pointing the way forward for the treatment of some of the more resistant cancers.
'There has been a lot of evidence that people who have a lot of fish in their diet have less instances of cancer. This discovery brings all of the pieces together. It gives us a handle on how the tumours work. It means we can attack the protein itself to maintain weight in patients and make them healthier.
'The discovery shows the tumours have an intelligence of their own and are producing something we didn't know about, something unique. Finding the exact structure of the protein and how the tumour cells work will help us devise an antibody to it. It is rather like a human Scud missile.'
The link between cancer and diet is now strong, and the CRC and others have invested heavily in projects to investigate the role of certain vitamins in cancer prevention. For example, vitamins A, C and E are important constituents of an anti-cancer diet.