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Cancer vaccines have come into the limelight this month with Merck, the US drugmaker, showing its drug Gardasil prevents the onset of cervical cancer. The fight against cancer, particularly in women, has taken a big step forward.
Merck's cancer vaccine prevents infection from two strains of the human papillomavirus (HPV), which helps cause cervical cancer in women. Gardasil has limitations in that it stops only two strains that cause about 70 per cent of cervical cancers, not all the 30 strains linked to the disease. However, data from the critical Phase III trials -- the final stage of trials necessary for regulatory approval -- showed Gardasil prevented pre-cancerous and cancerous lesions in all 5,300 women who took it.
The news was about as good as it can be for the pharmaceuticals industry. People around the world, usually uninterested in latestage clinical trial data, wanted to know more.
Gardasil is another step towards identifying the role of infectious agents (viral, bacterial or protozoan) in causing cancer and therefore being able to use a vaccine to eliminate the cause.
Cancer causes 7.0m deaths, or 12.5 per cent of deaths, around the world annually, according to the World Health Organisation (WHO), which forecasts 16m new cases a year by 2020, compared with 11m annually now.
Infections are a significant cause of cancer globally. Cancer-causing infections include the viruses HPV, Hepatitis B and C, EpsteinBarr, and HIV. About 15 per cent of cancer around the world in 1990 was attributed to infection, according to research led by D. Maxwell Parkin and Paola Pisani of the International Agency for Research of Cancer, published in the International Journal of Cancer. There are also ulcer-causing bacteria, such as Helicobacter pylori, and microscopic parasites.
Researchers also say there may be connections between infection and cancer awaiting discovery. "The fraction of human cancers attributable to infection may now need to be revised in light of the fact that new viral associations have been discovered and other non-viral associations have been identified," wrote David Persing and Franklyn Prendergast in Archives of Pathology and Laboratory Medicine in 1999.
Researchers see vaccination as an opportunity to use known scientific techniques to stop cancer.
Two approaches are being researched. The first is research for preventative vaccines for healthy patients, which seek to block a viral or other infection that can lead to cancer. The second is therapeutic vaccines, which try to programme the body's immune system to attack existing cancer cells, almost as if they were an infection.
Merck's Gardasil -- along with UK drugmaker GlaxoSmithKline's experimental Cervarix, also in late-stage trials -- are preventative vaccines for HPV, a virus connected with cervical cancer, the leading cause of death in women in the developing world. But it is not the first cancer vaccine. A preventative vaccine for Hepatitis B can prevent liver cancer. Research continues on a possible Hepatitis C vaccine, which could also prevent liver cancer.
Plenty of other infections that have been linked to cancer have no vaccine. The Epstein-Barr virus, which causes mononucleosis, has also been linked to rare cancers such as Burkitt's lymphoma. Kaposi's sarcoma and Bcell Lymphoma are linked to Herpes virus 8 in Aids patients.
Other potential links include human T-lymphotropic virus 1 and 2 and adult leukaemia and lymphoma. Stomach cancer has been associated with H pylori bacteria, which could be treated preventatively with antibiotics, while T-cell leukaemia has been linked with strongyloides stercoralis, an intestinal parasite.
Therapeutic vaccines have attracted a lot of research, but their development remains more difficult than developing preventative vaccines, says Doug Lowy, a US National Cancer Institute researcher. Therapeutic vaccines are more difficult because the body is already infected, and the challenge is to jump-start it to fight off the already established intruder. "All the vaccines we have that are approved [by regulators] are preventative vaccines," says Dr Lowy, who was involved in HPV vaccine research. "It's just harder to harness the immune system to make a therapeutic vaccine."
Current trials for therapeutic vaccines are targeting melanoma, kidney, lung and breast cancers, Hodgkin's and Non-Hodgkin's lymphoma, the NCI says.
Merck's Gardasil is not perfect, experts say, in that women will still require Pap cervical smear tests. There are also questions about pricing, and how public health authorities will respond to encouraging, and paying for, parents to have young girls vaccinated, as well as vaccinations for all uninfected women.
Nevertheless, the world's second vaccine for a dangerous cancer is expected to be approved next year in the US, and potentially to win approval in the European Union in 2007, with a third one in the shape o GSK's Cervarix close behind, bringing cancer vaccination into the mainstream.
Under syndication arrangement with FE
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