Explanation:
Hereditary breast cancer only represents a minority of breast cancer overall. Of the genes involved in the pathogenesis of this disorder, breast cancer susceptibility genes 1 or 2 (BRCA1 or BRCA2) are the most commonly encountered and account for most of these cases. These genes are also known to predispose patients to ovarian cancer, with ranges varying from 20 to 40% based on the gene mutated.
BRCA1 and BRCA2 are tumor suppressor genes that code for a protein functioning in DNA repair. When mutated, defective DNA repair leads to the development of cancerous cells. BRCA1 is located on chromosome 17, and BRCA2 is located on chromosome 13. Mutations of these genes are more prevalent in patients with Ashkenazi Jewish, French Canadian, or Icelandic heritage.
Microsatellite instability (A) is encountered in Lynch syndrome due to mutations affecting the MLH1, MSH2, MSH6,and PMS2 genes. Mutations that activate oncogenes (C) are also involved in carcinogenesis. RAS, for example, is the most common oncogene implicated in sporadic colorectal cancer. PTEN mutations (D) are seen in the setting of Cowden syndrome.
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