Overall, they include drugs that have long been abused, such as marijuana and cocaine, and drugs whose abuse is a more recent development. Some are stimulants, some depressants, and some hallucinogens-while most exhibit multiple pharmacological properties.
Studies of PCBs in humans have found increased rates of melanomas, liver cancer, gall bladder cancer, biliary tract cancer, gastrointestinal tract cancer, and brain cancer, [1] and may be linked to breast cancer. PCBs are known to cause a variety of types of cancer in rats, mice, and other study animals. [2].
Exposure to pollutants such as metals, dust, chemicals, or pesticides can increase the risk of cancer. At least four types of DNA viruses, hepatitis B and C viruses, Epstein-Barr virus, and human papillomavirus, are directly believed to cause human cancers. Nutrition is emerging as a way to help prevent cancer.