Major Genetic Syndromes
The EPHB2 gene is a target of the Wnt/beta-catenin signaling pathway and is important in the compartmentalization of intestinal epithelial cell proliferation to the intestinal crypts. When mice with disruption of the Ephb2 gene were bred with Apcmin/+ mice, tumor progression was accelerated suggesting that Ephb2 is a tumor suppressor whose loss of expression in the colon enhances adenoma progression.
Far more is known about the somatic molecular genetic alterations found in the colonic tumors occurring in HPPS patients. In a study of patients with either more than 20 HPs per colon, more than four HPs larger than 1 cm in diameter, or multiple (5-10) HPs per colon, a specific somatic BRAF mutation (V600E) was found in polyp tissue. Fifty percent (20 of 40) of HPs from these patients demonstrated the V600E BRAF mutation. The HPs from these patients also demonstrated significantly higher CpG island methylation phenotypes (CIMP-high), and fewer KRAS mutations than left-sided sporadic HPs. In a previous study from this group, HPs from patients with HPPS showed a loss of chromosome 1p in 21% (16 of 76) versus 0% in HPs from patients with large HPs (>1 cm), or only five to ten HPs.
Many of the genetic and histological alterations found in HPs of patients with HPPS are common with the recently defined CIMP pathway of colorectal adenocarcinoma. The CIMP pathway (identified molecularly by hypermethylation of specific genes such as CACNA1G, IGF2, NEUROG1, RUNX3, and SOCS1) is characterized histologically by a hyperplastic polyp-serrated adenoma-adenocarcinoma sequence.BRAF mutations are more commonly associated with the right colon and methylation of p16INK and MINT31.
Interventions/rare colon cancer syndromes
Individuals with Peutz-Jeghers and juvenile polyposis syndromes are at increased risk of CRC and extracolonic cancers. Because these syndromes are rare, there have been no evidence-based surveillance recommendations. Due to the markedly increased risk for colorectal and other cancers in these syndromes, a number of guidelines have been published based on retrospective and case series (i.e., based exclusively on expert opinion).[129,388,389,390,391] One's best clinical judgment must be used in making screening recommendations based on published guidelines.
Table 11. Clinical Practice Guidelines for the Diagnosis of Cancer in Peutz-Jeghers Syndrome
ACPGBI = Association of Coloproctology of Great Britain and Ireland; BE = barium enema; C = colonoscopy; FS = flexible sigmoidoscopy; NCCN = National Comprehensive Cancer Network.
a STK11 mutation analysis includes sequencing followed by analysis for deletions (e.g., MLPA), if no mutation found by sequencing.
bLung cancer risk is increased, but there are no recommendations beyond smoking cessation and heightened awareness of symptoms.
|Organization/ Author ||STK11 Gene Testing Recommendeda||Age Colon Screening Initiated||Frequency||Method||Extracolonic Screening Recommendations||Comment|
|ACPGBI||�||18 y||3 y||C or FS + BE||No mention of extracolonic screening||No mention of genetic testing; need to consider STK11/LKB1 testing|
|Brosens et al. ||Yes, age not specified||Late teens or at symptoms ||3 y||C||Breast, Gynecologic (Cervix, Ovaries, Uterus), Pancreas, Small Intestine, Stomach, Testes||Genetic testing at late teens or at symptoms|
|Giardiello and Trimbath ||Yes, at age 8 y||18 y||2-3 y||C||Breast, Gynecologic (Cervix, Ovaries, Uterus), Pancreas, Small Intestine, Stomach, Testes||�|
|NCCN ||No specific recommendation||Late teens||2-3 y||C||Breast, Gynecologic (Cervix, Ovaries, Uterus), Lungb, Pancreas, Small Intestine, Stomach, Testes ||Refer to specialized team|
|van Lier et al. ||�||25-30 y||�||C||Breast, Gynecologic (Cervix, Ovaries, Uterus), Pancreas, Small Intestine, Stomach||�|
|Zbuk and Eng ||�||18 y ||3 y||C||Breast, Gynecologic (Cervix, Ovaries), Pancreas, Small Intestine, Stomach, Testes||�|