• P53

p53 (also known as protein 53 or tumor protein 53), is a tumor suppressor protein that in humans is encoded by the TP53 gene. p53 is crucial in multicellular organisms , where it regulates the cell cycle and, thus, functions as a tumor suppressor that is involved in preventing cancer. p53 has many mechanisms of anticancer function, and plays a role in apoptosis, genomic stability, and inhibition of angiogenesis . If the P53 gene is damaged, tumor suppression is severely reduced.

• NF1 (neurofibromas, sarcomas, gliomas)
• NF2 (Schwann cell tumors, astrocytomas, meningiomas, ependymonas)
• STAT3 (many cancers)
• P16INK4a (many cancers)

• BRCA1 (breast and ovarian cancer)

BRCA1 (breast cancer 1), is a human caretaker gene that produces a protein called breast cancer type 1 susceptibility protein, responsible for repairing DNA. Certain variations of the BRCA1 gene lead to an increased risk for breast cancer as part of a hereditary breast-ovarian cancer syndrome. There have been identified hundreds of mutations in the BRCA1 gene, many of which are associated with an increased risk of cancer. Women with an abnormal BRCA1 gene have up to a 60% risk of developing breast cancer by age 90, while increased risk of developing ovarian cancer is about 55% for women with BRCA1 mutations. In addition to breast cancer, mutations in the BRCA1 gene also increase the risk of ovarian, fallopian tube, and prostate cancers. Mutations in BRCA1 are uncommon, and breast cancer is relatively common, so these mutations consequently account for only five to ten percent of all breast cancer cases in women. BRCA mutations can increase the risk of other cancers, such as colon cancer, pancreatic cancer, and prostate cancer. BRCA1 is a multifunctional protein that has been implicated in many normal cellular functions such as DNA repair, transcriptional regulation, cell-cycle checkpoint control and ubiquitination. Consequently, the presence or absence of functional BRCA1 has a significant effect on cellular response to chemotherapy. It was initially reported that overexpression of BRCA1 in human breast cancer cell lines resulted in increased resistance to cisplatin. Furthermore, antisense inhibition of endogenous BRCA1 expression promoted increased sensitivity to cisplatin that was associated with decreased DNA repair by NER and increased apoptosis. In addition, abrogation of BRCA1 protein expression using mRNA-specific ribozymes in HBL100 breast cancer cells resulted in increased sensitivity to both cisplatin and etoposide.

• BRCA2 (breast and ovarian cancer)

BRCA2 like BRCA1 is a human gene that belongs to a class of genes known as tumor suppressors.In normal cells, BRCA1 and BRCA2 help ensure the stability of the cell’s genetic material (DNA) and help prevent uncontrolled cell growth. Mutation of these genes has been linked to the development of hereditary breast and ovarian cancer. Not all gene changes, or mutations, are deleterious (harmful). Some mutations may be beneficial, whereas others may have no obvious effect (neutral). Harmful mutations can increase a person’s risk of developing a disease, such as cancer.A woman's risk of developing breast and/or ovarian cancer is greatly increased if she inherits a deleterious (harmful) BRCA1 or BRCA2 mutation. Men with these mutations also have an increased risk of breast cancer. Both men and women who have harmful BRCA1 or BRCA2 mutations may be at increased risk of other cancers. If a harmful BRCA1 or BRCA2 mutation is found, several options are available to help a person manage their cancer risk. In a family with a history of breast and/or ovarian cancer, it may be most informative to first test a family member who has breast or ovarian cancer. If that person is found to have a harmful BRCA1 or BRCA2 mutation, then other family members can be tested to see if they also have the mutation.

• PTEN

Phosphatase and tensin homolog ( PTEN ) is a protein that, in humans, is encoded by the PTEN gene .Mutations of this gene are a step in the development of many cancers . PTEN acts as a tumor suppressor gene. When the PTEN enzyme is functioning properly, it acts as part of a chemical pathway that signals cells to stop dividing and can cause cells to undergo programmed cell death ( apoptosis ) when necessary. These functions prevent uncontrolled cell growth that can lead to the formation of tumors. There is also evidence that the protein made by the PTEN gene may play a role in cell movement (migration) and adhesion of cells to surrounding tissues. PTEN is one of the most commonly lost tumor suppressors in human cancer. During tumor development, mutations and deletions of PTEN occur that inactivate its enzymatic activity leading to increased cell proliferation and reduced cell death. Frequent genetic inactivation of PTEN occurs in glioblastoma, endometrial cancer, and prostate cancer; and reduced expression is found in many other tumor types such as lung and breast cancer. Up to 70 percent of men with prostate cancer have lost one copy of the PTEN gene at the time of diagnosis. PTEN mutation also causes a variety of inherited predispositions to cancer. Mutations in the PTEN gene cause several other disorders that, like Cowden syndrome, are characterized by the development of noncancerous tumors called hamartomas .

• CDH1 (gastric cancer, lobular breast cancer)
• MEN1 (parathyroid and pituitary adenomas, islet cell tumors, carcinoid)