Lower gastrointestinal tract cancer predisposition syndromes

Microsatellite instability in colorectal cancer

Colorectal cancer (CRC) is a heterogeneous disease that is caused by the interaction of genetic and environmental factors. Although it is one of the most common cancers worldwide, CRC would be one of the most curable cancers if it is detected in the early stages. Molecular changes that occur in colorectal cancer may be categorized into three main groups: 1) Chromosomal Instability (CIN), 2) Microsatellite Instability (MSI), and 3) CpG Island Methylator phenotype (CIMP). Microsatellites, also known as Short Tandem Repeats (STRs) are small (1-6 base pairs) repeating stretches of DNA scattered throughout the entire genome and account for approximately 3 % of the human genome. Due to their repeated structure, microsatellites are prone to high mutation rate. Microsatellite instability (MSI) is a unique molecular alteration and hyper-mutable phenotype, which is the result of a defective DNA mismatch repair (MMR) system, and can be defined as the presence of alternate sized repetitive DNA sequences which are not present in the corresponding germ line DNA. The presence of MSI is found in sporadic colon, gastric, sporadic endometrial and the majority of other cancers. Approximately, 15-20 % of colorectal cancers display MSI. Determination of MSI status in CRC has prognostic and therapeutic implications. As well, detecting MSI is used diagnostically for tumor detection and classification. For these reasons, microsatellite instability analysis is becoming more and more important in colorectal cancer patients. The objective of this review is to provide the comprehensive summary of the update knowledge of colorectal cancer classification and diagnostic features of microsatellite instability.

Polyposis Syndromes: Role of the Pathologist

This article reviews the major gastrointestinal polyposis syndromes, with an emphasis on the molecular, clinical, and histopathological features of each. Salient features helpful in making or suggesting the diagnosis of these syndromes are discussed, as is the use of ancillary techniques, such as immunohistochemistry and molecular diagnostic studies in diagnosis confirmation and family screening.

Identification of patients at risk for hereditary colorectal cancer

Diagnosis of hereditary colorectal cancer syndromes requires clinical suspicion and knowledge of such syndromes. Lynch syndrome is the most common cause of hereditary colorectal cancer. Other less common causes include familial adenomatous polyposis (FAP), Peutz-Jeghers syndrome (PJS), juvenile polyposis syndrome, and others. There have been a growing number of clinical and molecular tools used to screen and test at risk individuals. Screening tools include diagnostic clinical criteria, family history, genetic prediction models, and tumor testing. Patients who are high risk based on screening should be referred for genetic testing.

Ovarian steroid cell tumor with biallelic adenomatous polyposis coli inactivation in a patient with familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant cancer predisposition syndrome that accounts for approximately 0.5-1% of all colorectal cancer cases. It is caused by germline mutations in the gene encoding the adenomatous polyposis coli (APC) tumor suppressor. Somatic APC inactivation due to mutation or loss of heterozygosity (LOH) promotes the development of adenomatous polyps by stabilizing the transcriptional coactivator β-catenin. Although colorectal cancer is by far the most common malignancy seen in FAP patients, the widespread use of prophylactic colectomy in these patients has increased the clinical importance of extracolonic tumors that are part of the neoplastic spectrum in FAP. Many of these tumors exhibit LOH or somatic APC mutation, strongly supporting a causative role of APC inactivation in their pathogenesis. Here we describe a 47-year-old female FAP patient with clinical manifestations of virilization who was found to have an ovarian steroid cell tumor, a rare neoplasm not known to be associated with FAP. Immunohistochemical analysis of the ovarian tumor demonstrated strong nuclear β-catenin staining consistent with somatic APC inactivation, and molecular analysis confirmed biallelic APC inactivation in the tumor. Our findings provide the first evidence that ovarian steroid cell tumors may be an extracolonic manifestation of FAP and implicate β-catenin activation as an oncogenic mechanism in ovarian steroid cell tumorigenesis.