Germline TP53 mutations were identified in 17% (n = 91) of 525 samples submitted to City of Hope laboratories for clinical TP53 testing. All families with a TP53 mutation had at least one family member with a sarcoma, breast cancer, brain cancer, or adrenocortical cancer (core cancers). In addition, all eight individuals with a choroid plexus tumor had a TP53 mutation, as did 14 of the 21 individuals with childhood adrenocortical cancer. In women aged 30 to 49 years who had breast cancer but no family history of other core cancers, no TP53 mutations were found. TP53 mutations are uncommon in women with breast cancer before age 30 years with no other indications for TP53 screening (e.g., a family history of sarcoma). In three studies, the numbers of women with TP53 mutations were 0 (of 95), 1 (of 14), and 2 (of 52).[275,276,277]
Located on chromosome 17p, TP53 encodes a 53kd nuclear phosphoprotein that binds DNA sequences and functions as a negative regulator of cell growth and proliferation in the setting of DNA damage. It is also an active component of programmed cell death. Inactivation of the TP53 gene or disruption of the protein product is thought to allow the persistence of damaged DNA and the possible development of malignant cells. Evidence also exists that patients treated for a TP53-related tumor with chemotherapy or radiation therapy may be at risk of a treatment-related second malignancy. Germline mutations in TP53 are thought to account for fewer than 1% of breast cancer cases. HER2 overexpression may be common in Li-Fraumeni-associated breast cancer.
Screening for breast cancer with annual magnetic resonance imaging is recommended; additional screening for other cancers has been studied and is evolving.[281,282]
One of the more than 50 cancer-related genodermatoses, Cowden syndrome (OMIM) is characterized by multiple hamartomas, an excess of breast cancer, gastrointestinal malignancies, endometrial cancer, and thyroid disease, both benign and malignant.[283,284] Lifetime estimates for breast cancer among women with Cowden syndrome range from 25% to 50%. As in other forms of hereditary breast cancer, onset is often at a young age and may be bilateral. Skin manifestations include multiple trichilemmomas, oral fibromas and papillomas, and acral, palmar, and plantar keratoses. History or observation of the characteristic skin features raises a suspicion of Cowden syndrome. Central nervous system manifestations include macrocephaly, developmental delay, and dysplastic gangliocytomas of the cerebellum.[286,287] Germline mutations in the PTEN gene (OMIM), which is located on chromosome 10q23 and encodes a tyrosine phosphatase protein with homology to tensin, are responsible for Cowden syndrome. Loss of heterozygosity at the PTEN locus observed in a high proportion of related cancers suggests that PTEN functions as a tumor suppressor gene. Its defined enzymatic function indicates a role in maintenance of the control of cell proliferation. Disruption of PTEN appears to occur late in tumorigenesis and may act as a regulatory molecule of cytoskeletal function. Although PTEN mutations, which are estimated to occur in 1 in 200,000 individuals, account for a small fraction of hereditary breast cancer, the characterization of PTEN function will provide valuable insights into the signal pathway and the maintenance of normal cell physiology.[284,289] (Refer to the Major Genes section in the PDQ summary on Genetics of Colorectal Cancer for more information about Cowden syndrome.)