Cancer

 What we know
 Incidence
 Environmental risk factors

What we know

Cancer is a generic term that refers to a group of diseases that occurs when cells in the body begin to grow out of control. Many processes control cell division and growth. Cancer generally occurs when several of the genes controlling these cell division and growth mechanisms are damaged, enabling a cell to grow and divide uncontrollably. Cancer can be benign or malignant. Those that are malignant have the ability to invade surrounding and distant tissues and organs.

There are over two hundred types of cancer. They are grouped as:

 Adenomas, tumours arise in glandular tissue like the thyroid, the pituitary gland the adrenal gland. They are often benign.
 Carcinomas, the most common types of cancer, come from the cells that cover external and internal body surfaces. They include lung, breast, and colon cancer.
 Sarcomas arise from cells found in the supporting tissues of the body such as bone, cartilage, fat, connective tissue and muscle.
 Lymphomas are cancers arising in the lymph nodes and tissues of the body’s immune system.
 Leukaemias develop in the immature blood cells that grow in the bone marrow.

Figure 1 Numbers of newly diagnosed cases of cancer in the EU, by cancer site. [1], Cancer Research UK Enlarge the picture,

Figure 2 Time trends of cancer incidence in children (age 0-14). Age-standardized rates, Europe. [2] Enlarge the picture

Incidence

Worldwide, cancer is responsible for 7.6 million deaths. In Europe there are 3 million new cancer cases per year (30 Countries), with 2 million new cases in the EU25 alone. Approximately one in four deaths in the EU is from cancer and in 2004 the disease caused more than 1.7 million deaths. After Cardiovascular diseases (CVD), cancer is the second main cause of death. [3], [4] The most common types of cancer are Colorectal (bowel) cancers. Among men lung/trachea/bronchus cancers are most common. Among women breast cancer is the most common [5].

Studies indicate that overall, the incidence of cancer is rising. A report published in the Annals of Oncology estimates that there were 3.2 million new cases of cancer in 2006, up from 2.9 million in 2004 [6]. What is more, the incidence of childhood cancers is increasing [7].

Cancer is a multifactor disease caused by changes in the genes responsible for cell division growth and repair. These changes can occur as a result of hereditary, lifestyle and environmental factors.

Environmental risk factors

Whilst there is no single cause of cancer, the disease has long been linked to environmental factors like cigarette smoking, and chemical exposures such as asbestos, vinyl chloride and dioxins, a group of chemicals formed unintentionally in industrial processes. Each of these risk factors acts by either altering the DNA or promoting uncontrolled cell division and growth.

However, evidence is now emerging that chemicals used in the home, in agriculture, and other chemical residues that pollute the environment may be contributing to the increasing cancer burden. Among those implicated are metals like hexavalent chromium, solvents such as and tetrachlorethylene and chlorinated hydrocarbons, pesticides, PCBs, combustion by-products such as benzene, and endocrine disrupting chemicals such as phthalates and Bisphenol A (BPA) that mimic or disrupt the body’s hormone signalling pathways [8], [9].

Every day we are exposed to thousands of different chemicals that combine in a chemical cocktail in the human body. Some researchers assert that chemicals present at low doses are unlikely to cause cancer. However, the potential additive and synergistic effects of the variety of chemicals to which we are exposed mean that low potency should not be used as a marker for the carcinogenic potential of these chemicals.

Furthermore, research on radiation has established that exposure before the age of 20 is highly significant whist exposures after the age of 40 have little detectable effect. Thus, even if healthy adults are not at risk from certain chemicals, involuntary exposure to these contaminants may put the more vulnerable in society at risk: the developing foetus, the developing child and adolescent and genetically predisposed.

In many instances cancer can be prevented, through a healthy diet, environment and physical activity. According to the WHO, one third of the cancer burden could be prevented by reducing exposure to risk factors [10]. Whilst there is much to learn about chemical carcinogenesis, the growing body of evidence suggests that preventive action to reduce chemical exposures may help reduce the growing burden of cancer.

 For more information please see the Collaborative on Health and Environment Cancer Working Group