Fundamentals of Cancer Detection, Treatment, and Prevention. Surya K. De
pollution is defined as the presence of poisonous chemicals or compounds (organic or inorganic) in the air we breathe, at levels that pose a health risk. Air contaminated with pollution, which can exist as particulates, biological molecules, or gases, can lead to various types of cancer [105,106]. One example is soot, which is contaminated carbon particles resulting from incomplete burning of organic material. Even as long ago as the 1770s, chimney sweeps in London were developing scrotal cancer at higher rates than in the general population. Inhalation of soot has also been linked to lung, esophageal, and bladder cancers.
2.13.2 Certain Types of Plastic
These can be dangerous in terms of exposing humans to carcinogenic substances, especially when plastic containers become scratched or cracked, allowing chemicals to be leached out. One example is bisphenol A (BPA), a synthetic estrogen that has been used in many plastics and resins since the 1960s. BPA resins can be used inside products like metal food cans as sealants, while polycarbonate BPA plastics can include water bottles and food storage containers. BPA can even be found in thermal paper receipts, where it is used to stabilize the ink.
The safety of BPA has been controversial, as studies have found it is linked to obesity, diabetes, problems with fertility and reproductive organs, susceptibility to various cancers, and cognitive/behavioral deficits like attention deficit hyperactivity disorder (ADHD).
While many plastic manufacturers have started labeling their products “BPA‐free,” the compound is still very commonly used in a broad array of consumer products.
2.13.3 Acrylamide
It is a chemical mainly used to make substances called polyacrylamide and acrylamide copolymers, which are used in several types of industrial processes, including the production of paper, dyes, and plastic. They are also found in some consumer items like caulking and food packaging.
In addition, acrylamide is found in some foods. The main foods containing acrylamide are French fries and potato chips, crackers, bread, cookies, breakfast cereals, canned black olives, prune juice, and coffee. It can be created when vegetables that contain the amino acid asparagine are heated to high temperatures in the presence of certain sugars. The browning of meat generates acrylamide as a byproduct of the chemical reaction called the Maillard reaction, which occurs during the browning process (Figure 2.18) between asparagine and reducing sugar [123–126]. The carbonyl group of the sugar reacts with the amino group of the amino acid to form an N‐substituted glycosylamine, which undergoes Amadori rearrangement to produce a ketosamine. The open‐chain ketosamine further undergoes dehydration and deamination steps to give a reactive dicarbonyl compound. This dicarbonyl reacts with an asparagine to produce a Schiff base, which further degrades through Maillard reaction to produce toxic acrylamide (Scheme Scheme 2.1). Acrylamide can react with cysteine or lysine and damage normal DNA.
Figure 2.18 Browning of meat produces acrylamide and it can cause cancer.
Scheme 2.1 Formation of acrylamide, a byproduct of Maillard reaction between reducing sugars and amino acids.
Tobacco smoke from cigarettes, however, is a much more significant source of exposure to acrylamide than food.
In studies using rodent models, acrylamide exposure was linked to an increased risk of developing several types of cancer [107–117]. According to the National Toxicology Program's Report on Carcinogens, acrylamide is likely carcinogenic based on its effect in laboratory animals given drinking water contaminated with this compound. More studies, however, need to be done to find out the levels and length of exposure required to affect humans.
Certain occupations involve more employee contact with cancer‐causing substances. Some workers are exposed daily. A few occupations at higher risk include aluminum workers, painters, tar pavers (who are exposed to carcinogenic benzene), rubber and plastic manufacturers, hairdressers, and manicurists in nail salons.
2.14 Possible Human Carcinogens
A carcinogen is any substance that promotes carcinogenesis, the formation of cancer. An English physician John Hill first observed in 1761 that certain chemical exposures have been linked to the development of cancer [118]. He noted that the snuff users developed nasal cancer more frequently than the general population. Over 100 000 chemicals are used, and about 1000 new chemicals are listed each year, but not all chemicals are carcinogens. These chemicals are found in everyday items, including as foods, personal products, packaging, prescription drugs, and household and lawn care products [119–122]. While some chemicals may be harmful, not all contact with chemicals is dangerous to your health. Examples of known human carcinogens are asbestos, arsenic, benzene, beryllium, cadmium, nickel, vinyl halides, and others. Examples of possible human carcinogens are chloroform, DDT, polycyclic aromatic hydrocarbons, aromatic amines, azo dyes, nitrosamines and nitrosamides, hydrazo and azoxy compounds, carbamates, halogenated compounds, natural products, and others. DNA bases such as purine and pyrimidine are nucleophiles and react with any electrophiles resulting in DNA damage. Some reactive chemicals such as alkylating agents (alkyl halides), aldehydes, and others directly make a covalent bond with nucleophilic sites in the purine and pyrimidine rings of nucleic acids. Some chemicals react with DNA after being metabolized by the liver cytochrome P450 enzymes. For example, some alkenes and polycyclic aromatic hydrocarbons are metabolized by human liver enzymes to produce an electrophilic epoxide. DNA attacks the epoxide and is bound permanently to it and damages normal cells.
An estimation of some factors contributing to cancer development and their relative significance is shown in (Figure 2.19).
2.15 Guidelines for Early Detection of Cancer
The following are the current American Cancer Society guidelines for early detection of cancer in most men and women:
Figure 2.19 Factors contributing to cancer development and their relative significance.
| Women aged 20–29: | Breast exam and Pap test (for cervical cancer) every 1–3 yr. |
| Women aged 30–39: | Mammograms (X‐rays of the breast) every 1–3 yr, Pap test and HVP test every 5 yr. |
| Women aged 40–49: | Breast test every year, Pap and HPV test every 5 yr. |
| Women aged 50–75: | Mammograms every year, Pap and HPV test every 5 yr, colonoscopy every 10 yr, colon CT scan every 5 yr.a) |
| Women aged 76+: | Your doctor will decide. |