In 1981, Sir Richard Peto and Sir Richard Doll, the famous British researchers, estimated that tobacco accounted for about 30% of cancers. But a French medical oncologist, Professor Dominique Belpomme, told the PAN conference he had calculated that tobacco now only caused between 15 and 20% of cancers.

These figures would be similar in other industrialised countries, and Professor Belpomme – president of the French Association for Research on Treatments Against Cancer (ARTAC) – argued that governments in these countries should now focus more on the relationship between the environment and health.In France, deaths from cancer had doubled since the Second World War and now stood at 150,000 people each year. At the same time, cancer incidence had increased dramatically during the last 20 years and there were now 280,000 new cases a year. “

According to Sir Richard Peto and Sir Richard Doll, tobacco is classically considered as the main cause of cancer. However, I have calculated that in France, cancer causes only 15 to 20% of new cases and no more than 20% of cancer deaths each year.” Genetic factors accounted for only 5 to 10% of cancer cases, and it had been shown that some viral contaminations could explain the occurrence of another 10%, including primary liver cancer, leukaemia and lymphoma. Natural and artificial radioactivity could account for another 10% of cancer cases, including soft tissue sarcoma, leukaemia and lymphoma.

“These factors alone cannot contribute to the recent increase in cancer incidence. So, it is clear that environmental factors are involved, mainly through feeding or pollution of the environment, home or at work.” The chemicals involved include polycyclic aromatic hydrocarbons, polyvinyl chloride, some heavy metals, nitrates, nitrites, dioxins, some food additives and pesticides. Some pesticides have been classified as carcinogenic by international organisations including the Environmental Protection Agency of the United States and the International Agency for Cancer Research in France. Prof. Belpomme explained that the arguments which allowed these international organizations to link pesticides exposure to carcinogenesis have emerged from both epidemiological and toxicological approaches, because the link proved by the first approach is only associative, while the second is causal. “That means that we need both complementary approaches to establish definitely such a link, at a scientific level”.

“Furthermore, an increasing number of epidemiological hot spot studies strongly suggest that pesticide exposure is associated with several types of cancers, including leukaemia, soft tissue sarcoma, brain tumours, testicular cancer and child cancers. The involvement of pesticides in the increased incidence of prostate or breast cancers has still to be determined.”

Professor Belpomme argued that the precautionary principle demanded that pesticides from the L1 and L2 group of the US EPA classification and those from group I, IIA and IIB of the IARC classification should be prohibited[1]. He explained that cancer genesis is related to two different mechanisms:

• initiation (mutations)
• promotion (growth of mutated cells)

In addition to their chemically-linked, direct mutagenic effect, many pesticide molecules may cause cancer because of their endocrine-disrupting (ED) related hormonal effect, through different mechanisms, depending on dose and timing of exposure. At high dose exposure, it is well known that oestrogenic molecules can “initiate” cancer cells, due to their mutagenic properties, whereas at long-term, low dose exposure, they can ”promote” growth of hormonal-dependent cancer cells. Therefore, the ED-related mutagenic effect of pesticides should be dose-dependent and cause initiation of cancer at high dose, as it could be the case when pesticides exposure occurs at some critical physiological period of the embryo development. In contrast, the cancer promotion effect of pesticides, which is not dose-dependent, could result from a long term exposure at very low doses, in people who bear already initiated cells in their body, whatever the origin and cause of the mutations.

Professor Belpomme represents ARTAC and PAN Europe on the European Commission’s technical working group on endocrine disruptors, as part of the Commission’s Environment & Health Strategy set up in 2003. This TWG concentrates on the integrated monitoring of endocrine disrupting chemicals. However, Prof. Belpomme and certain others are unhappy about the position of some members of the TWG. Some scientists want to have definitive proof of the ED effects in humans, a German representative from the Bayer group wants to consider that nothing is demonstrated about the pesticides-related effects on health, while the chairman of this group is not a clinician and appears to be more interested in getting money from Europe through biomonitoring rather than contributing efficiently to improve public health. Prof. Belpomme has written a letter to the group chairman and other members pointing out the need to consider the cancer-causing properties of these chemicals as well as their endocrine-disrupting ones.

Finally, Professor Belpomme explained that he is contributing to the French national anti-cancer programme agreed by President Jaques Chirac and run by the French health ministry. Professor Belpomme is in charge of the environmental part of the programme, and has already argued that pesticides should be a top priority. He asked PAN Europe to help by contributing to a “scientifically sound” database linking pesticides to their health effects. To discuss his concerns further, Professor Belpomme and ARTAC are organising an international meeting on the links between cancer and the environment – examining the role of pesticides in particular – on May 7 2004 at UNESCO in Paris.

[1] L1 category = “likely at High doses, but not likely at low dose” and L2= “likely to be carcinogenic to humans, available tumour effects and other key data are adequate to demonstrate carcinogenic potential for humans”. The IARC categories are group I = Carcinogenic to humans, Group IIa = Probably carcinogenic to humans (limited evidence of carcinogenicity in humans and sufficient evidence in experimental animals) and IIB= Possibly carcinogenic to humans (limited evidence of carcinogenicity in humans and less than sufficient evidence in experimental animals)