Cancer chemoprevention drugs have been applied for over 30 years to prevent cancer, essentially for typical high risk prevention or pre-cancerous tissues developing into invasive cancers (Table 9).
The anti-insulin drug Metformin has anti-insulin and insulinlike growth factors, which can be applied to prevent the occurrence of a second primary cancer for oestrogen receptornegative breast cancer patients. Analysis of 11 papers shows that diabetic patients receiving Metformin treatment have a lower risk of cancer by 31% than those receiving other antidiabetic treatments. It has been found that the drug can be used as adjuvant therapy for breast, pancreatic and lung cancer.
Tamoxifen or Raloxifene is mainly used for estrogen receptorpositive breast cancer patients who accepted surgical resection and those women who are at high risk of breast cancer such as people who have the risk through positive genetic testing and people who have a family history of breast cancer. The preventive effects of these two drugs are similar, but Raloxifene is less toxic. The third- generation aromatase inhibitors have come out: Exemestane and Anastroozole, these two drugs can prevent occurrence of contralateral breast cancer for those patients who had breast cancer in one breast. According to the research of the Canadian Institute for Cancer Research, Exemestane can decrease the invasive breast cancer incidence by 65% for high-risk postmenopausal women and drop the estrogen receptor-positive breast cancer incidence by 73%.
It has been demonstrated that aspirin can prevent cancer. A daily intake of aspirin (regardless of the dose) for a consecutive five years can reduce the cancer incidence by 44%, especially having a most preventive effect on gastrointestinal cancers (oesophageal cancer and colorectal cancer). Aspirin can significantly reduce cancer recurrence or new adenomas for people who have suffered from colorectal cancer or colorectal adenomas.
Except for aspirin, other non-steroidal anti-inflammatory drugs such as Celecoxib can reduce the adenoma incidence after polypectomy for people who had familial adenomatous polyposis. But the drug has cardiovascular toxicity, so longterm administration of this drug is not recommended.
5α reductase inhibitors Finasteride and Dutasteride can be used for benign prostatic hyperplasia, reducing the prostate cancer incidence by 25%. But for patients who had prostate cancer, these two drugs can upgrade the tumor and increase the malignancy degree. Therefore these drugs application should be fully measured.