Serrated polyps of the colon

Serrated Polyps of Colon and Rectum: a Clinicopathologic Review

BACKGROUND

In the past decade, there have been significant changes in the classification and nomenclature of colorectal polyps. Previously, only two groups of lesions were widely recognized, the adenoma and the hyperplastic polyp. Adenomas were considered the only precursor of colorectal cancer, and hyperplastic polyps were considered innocent with no malignant potential. However, recent discoveries about molecular pathways of colorectal cancers have significantly changed our understanding of these neoplasms. Serrated polyps-previously uniformly called hyperplastic polyps-are now known to comprise a heterogeneous family of neoplasms united by their characteristic saw tooth morphology but differing in many important ways, including their malignant potential and molecular profile. This group of neoplasms includes both hyperplastic polyps and the more recently recognized serrated adenomas. Serrated adenomas can be subdivided into the traditional serrated adenoma and the sessile serrated adenoma/polyp. Both of these lesions show characteristic molecular changes, which differ from traditional colorectal adenomatous polyps.

OBJECTIVES

In this review, we will discuss the morphologic features of serrated colorectal lesions, the molecular alterations that characterize them, and their role in colorectal cancer development.

MATERIAL AND METHODS

The English literature regarding the new nomenclature will be reviewed and the key diagnostic points will be recorded.

RESULTS AND DISCUSSION

This large group of polyps has recently been better classified which needs specific attention by pathologists, gastroenterologists and even surgeons.

Evaluation of the Effectiveness and Cost-Effectiveness of Personalized Surveillance After Colorectal Adenomatous Polypectomy

Lifetime risk of developing colorectal cancer is 5%, and 5-year survival at early stage is 92%. Individuals with precancerous lesions removed at primary screening are typically recommended surveillance colonoscopy. Because greater benefits are anticipated for those with higher risk of colorectal cancer, scope for risk-specific surveillance recommendations exists. This review assesses published cost-effectiveness estimates of postpolypectomy surveillance to consider the potential for personalized recommendations by risk group. Meta-analyses of incidence of advanced neoplasia postpolypectomy for low-risk cases were comparable to those without adenoma, with both rates under the lifetime risk of 5%. This group may not benefit from intensive surveillance, which risks unnecessary harm and inefficient use of often scarce colonoscopy capacity. Therefore, greater personalization through deintensified strategies for low-risk individuals could be beneficial. The potential for noninvasive testing, such as fecal immunochemical tests, combined with primary prevention or chemoprevention may reserve colonoscopy for targeted use in personalized risk-stratified surveillance. This review appraised evidence supporting a program of personalized surveillance in patients with colorectal adenoma according to risk group and compared the effectiveness of surveillance colonoscopy with alternative prevention strategies. It assessed trade-offs among costs, benefits, and adverse effects that must be considered in a decision to adopt or reject personalized surveillance.

MicroRNA Signatures of Colonic Polyps on Screening and Histology

Colorectal cancer and adenoma adjacent to cancer exhibit distinct microRNA (miRNA) alterations in an apparent mucosa-to-adenocarcinoma sequence. The pattern of microRNAs in screen-detected polyps in relation to histologic features and cancer risk has not been investigated. miRNA expression analysis was performed on normal mucosa (NM), hyperplastic polyps (HP), tubular adenomas (TA), tubulovillous adenomas or high-grade dysplasia (TVHG), and serrated polyps [sessile serrated adenoma/polyps (SSA/P) and traditional serrated adenomas (TSA)] in biopsy specimens from 109 patients undergoing screening/surveillance colonoscopy. Generalized linear models were used to identify differentially expressed miRNAs by histologic type and logistic regression to identify miRNA predictors of histopathology. False discovery rate (FDR) was used to control for multiple comparisons. We identified 99 miRNAs differing in at least one of five histopathologic groups (FDR ≤0.05). In a comparison of HPNM versus TVHG, the top most upregulated and downregulated miRNAs in HPNM included miR-145, -143, -107, -194, and -26a (upregulated), and miR-663, -1268, -320b, -1275, and -320b (downregulated; FDR P < 0.05). miR-145 and -619 showed high accuracy to discriminate low- from high-risk polyps without serrated histology (TVHG vs. HPNM + TA; CI, 95.6%), whereas miR-124, -143, and -30a showed high accuracy of separating high-risk polyps (TVHG + TSA) from low-risk polyps (HPNM + TA + SSA/P; CI, 96.0%). For TSAs, miR-125b and -199a were uniquely downregulated relative to HPNMs, and miR-335, -222, and -214 discriminated between non-serrated and serrated histology. Our data support the presence of colorectal cancer-associated miRNA alterations in screen-detected adenomas that may be useful for risk stratification for surveillance interval planning. Cancer Prev Res; 9(12); 942-9. ©2016 AACR.

Gut microbiome and colorectal adenomas

The trillions of bacteria that naturally reside in the human gut collectively constitute the complex system known the gut microbiome, a vital player for the host's homeostasis and health. However, there is mounting evidence that dysbiosis, a state of pathological imbalance in the gut microbiome is present in many disease states. In this review, we present recent insights concerning the gut microbiome's contribution to the development of colorectal adenomas and the subsequent progression to colorectal cancer (CRC). In the United States alone, CRC is the second leading cause of cancer deaths. As a result, there is a high interest in identifying risk factors for adenomas, which are intermediate precursors to CRC. Recent research on CRC and the microbiome suggest that modulation of the gut bacterial composition and structure may be useful in preventing adenomas and CRC. We highlight the known risk factors for colorectal adenomas and the potential mechanisms by which microbial dysbiosis may contribute to the etiology of CRC. We also underscore novel findings from recent studies on the gut microbiota and colorectal adenomas along with current knowledge gaps. Understanding the microbiome may provide promising new directions towards novel diagnostic tools, biomarkers, and therapeutic interventions for CRC.

Impact of the consideration of serrated polyps to the interval of colonoscopic surveillance in the NHS Bowel Cancer Screening Programme

AIM

Most international post polypectomy surveillance guidelines do not recommend surveillance for serrated polyps. In the present study the additional impact of serrated polyps on surveillance intervals from international adenoma surveillance guidelines was investigated.

METHOD

Endoscopic and pathology records were audited of participants in the NHS Bowel Cancer Screening Programme (guaiac faecal occult blood test, gFOBT) in 2011. Surveillance intervals were calculated for current guidelines and also for serrated polyps based on previously described aggressive and conservative strategies.

RESULTS

In total, 389 patients were included of whom 141 (36.2%) were high risk (advanced adenoma: adenoma ≥ 10 mm, villous elements, high grade dysplasia, or adenoma ≥ 3 in number) needing surveillance at ≤ 3 years. Thirty-three (8.5%) had significant serrated polyps, of whom 18 (4.6% of the total) had significant serrated lesions and simultaneous advanced adenoma or ≥ 3 adenomas. Adopting an aggressive surveillance strategy, the mean overall absolute additional proportion of all such patients in the surveillance group at 3 years or less was 4.0% (3.9% - 4.1%; 4.2% women; 3.8% men). These proportions varied according to endoscopist from 2.3% to 4.7%. For more conservative strategies the increase was only 1%.

CONCLUSION

The impact of including serrated polyps in current guidelines would result in a small increase in surveillance intervals for FOBT based bowel cancer screening. About half of those who might need surveillance for serrated polyps would already receive surveillance for being in a high risk adenoma group.

Colorectal polyps and polyposis syndromes

A polyp is defined as any mass protruding into the lumen of a hollow viscus. Colorectal polyps may be classified by their macroscopic appearance as sessile (flat, arising directly from the mucosal layer) or pedunculated (extending from the mucosa through a fibrovascular stalk). Colorectal polyps may also be histologically classified as neoplastic or as non-neoplastic (hyperplastic, hamartomatous, or inflammatory). The neoplastic polyps are of primary importance because they harbor a malignant potential, which represents a stage in the development of colorectal cancer. For this reason, it is essential to identify these polyps at a sufficiently early stage, when a simple outpatient procedure to remove them can interrupt the development of colorectal cancer and prevent disease and death. When invasive carcinoma arises in a polyp, careful consideration must be given to ensuring the adequacy of treatment. Although most neoplastic polyps do not evolve into cancer, it is well accepted that the majority of colorectal carcinomas evolve from adenomatous polyps; the sequence of events leading to this transformation is referred to as the adenoma-to-carcinoma sequence.

The presence of a systemic process that promotes the development of multiple gastro-intestinal polyps is termed ‘polyposis’. Hereditary gastro-intestinal polyposis syndromes account for approximately 1% of all cases of colorectal cancer and are associated with a broad spectrum of extra-colonic tumors. Early detection and accurate classification of these syndromes are essential, in order to initiate a surveillance program for the early detection of cancer. Several polyposis syndromes have been described, each having its own genetic basis and characteristic polyp distribution, clinical presentation, and malignancy risk.

Diagnostic modalities and treatment options for neoplastic polyps—as well as the most prevalent polyposis syndromes—are reviewed below.

Autophagy and hypoxia in colonic adenomas related to aggressive features

AIM

The study investigated whether autophagic activity and hypoxia parallel the adenoma-carcinoma sequence.

METHOD

The study comprised 120 tubular adenomas with high-grade dysplasia, including 22 with questionable evidence of invasion, 37 with definite stromal invasion and 29 with severely dysplastic adenoma, 10 traditional serrated adenomas and 22 classical tubular adenomas lacking aggressive features. The samples were stained immunohistochemically for autophagy (LC3A and Beclin-1) and hypoxia-inducible factor1-alpha (HIF1α) markers.

RESULTS

LC3A was detected as diffuse cytoplasmic staining and as dense "stone-like" structures (SLS) within cytoplasmic vacuoles. Beclin-1 reactivity was purely cytoplasmic, whereas that of HIF1α was both cytoplasmic and nuclear. SLS counts in noninvasive, nontransformed areas of tubular adenomas were consistently low (median SLS = 0.5; 200× magnification), whereas a progressive increase was noted from areas of equivocal invasion (median SLS = 1.3; 200× magnification) and intramucosal carcinoma (median SLS = 1.4; 200× magnification) to unequivocal invasive foci (median SLS = 2.1; 200× magnification) (P < 0.0001). A similar association was shown for Beclin-1 and HIF1α expression (P < 0.05). Traditional serrated adenomas yielded low SLS counts and weak HIF1α reactivity, but high cytoplasmic LC3A and Beclin-1 expression (P < 0.01).

CONCLUSION

A hypoxia-driven autophagy in adenomatous polyps, when particularly intense and localized, is commonly associated with early invasion or severely dysplastic adenoma.

Serrated polyps: new classifications highlight clinical importance

AIM

Many lesions previously classified as hyperplastic polyps and therefore thought to be innocuous have been reclassified as sessile serrated adenomas/polyps (SSA/Ps), establishing their place in the serrated pathway and underscoring their malignant potential. The clinical relevance of this new nomenclature is incompletely defined. This study examines the incidence and characteristics of colorectal SSA/Ps and describes other associated colorectal neoplasia.

METHOD

A single institution pathology database was searched for the diagnosis of SSA/Ps between January 2004 and October 2007. SSA/Ps found by colonoscopy were included. Patient demographics, SSA/P characteristics and associated colonoscopic findings were retrospectively recorded.

RESULTS

A total of 585 SSA/Ps were removed during 519 colonoscopies in 483 patients performed by 64 different endoscopists. This represented an overall incidence of SSA/Ps per colonoscopy of 2.1% in the 28,054 colonoscopies performed during the study period. The median SSA/P size was 0.8 cm (range 0.2-4.5) and 188 (69%) were ≥ 1.0 cm. Of the 585 SSA/Ps, 366 (63%) were right-sided, 129 (22%) were in the left colon and 90 (15%) were in the rectum. Also, 439 synchronous polyps of other histology (mainly adenomas and hyperplastic polyps) were found during the same 519 colonoscopies.

CONCLUSION

SSA/Ps are rare lesions found during colonoscopy that may coexist with small hyperplastic polyps. Because SSA/Ps are part of the serrated oncogenic pathway, all, even those appearing to be hyperplastic, should be removed or biopsied for diagnosis. Careful review of historical lesions with application of new definitions may redefine risk for malignancy.

Intermediate methylation epigenotype and its correlation to KRAS mutation in conventional colorectal adenoma

A subset of colorectal cancer shows significant accumulation of aberrant promoter methylation. Previously, we developed two groups of methylation markers that classified colorectal cancer into three epigenotypes: i) high-, ii) intermediate-, and iii) low-methylation epigenotypes. High-methylation epigenotype, with methylation of both group 1 and group 2 markers, correlates to BRAF-mutation((+)). Intermediate-methylation epigenotype, with methylation of group 2 markers, but not group 1, correlates to KRAS-mutation((+)). To gain insight into epigenotype development in colorectal carcinogenesis, especially intermediate-methylation epigenotype and its correlation to KRAS-mutation((+)) in adenoma, we analyzed methylation levels of group 1 and group 2 markers quantitatively by matrix assisted laser desorption ionization-time of flight mass spectrometry, in 51 adenomas, 13 aberrant crypt foci, and 26 normal mucosa samples, and we compared them to 149 previously analyzed colorectal cancer samples. Three serrated adenomas were all BRAF-mutation((+)), showing great methylation of group 1 and group 2 markers, thus high-methylation epigenotype. Forty-eight conventional adenomas were not methylated in group 1 markers and were classified into two clusters with higher and lower methylation of group 2 markers, thus into intermediate- and low-methylation epigenotypes, respectively. Adenoma with intermediate-methylation epigenotype correlated to KRAS-mutation((+)). Methylation levels of group 2 markers in adenoma were higher than aberrant crypt foci and normal samples, but similar to cancer. These data suggested that epigenotype development occur at an earlier stage than carcinoma formation, and already be completed at the adenoma stage. Intermediate methylation epigenotype and its correlation to KRAS-mutation((+)) were developed in conventional adenoma.

Serrated polyps: critical precursors to colorectal cancer

Colorectal polyps have been traditionally classified as either hyperplastic or adenomatous, with only the latter progressing to carcinoma. However, it is now recognized that certain subtypes of serrated polyps have a risk of malignant transformation via a serrated neoplasia pathway. Serrated polyps are a heterogeneous group of lesions with distinct morphologic, histologic and molecular genetics profiles. Based on available evidence, there are reasons to suspect that this pathway may contribute to interval or missed cancers because serrated lesions are more likely than conventional adenomas to be missed on colonoscopy, and the progression of serrated polyps to cancer may be more rapid. Therefore, it is paramount that physicians recognize the importance of serrated polyps and are aware of the latest surveillance guidelines.

Prognostic and predictive impact of DNA mismatch repair in the management of colorectal cancer

Colorectal cancers develop via two major pathways that include chromosomal instability and microsatellite instability. Microsatellite instability occurs due to deficient DNA mismatch repair (MMR), which can be caused by epigenetic silencing of the MLH1 MMR gene in sporadic colorectal cancers or germline mutations in MMR genes that result in Lynch syndrome. While the molecular origin of deficient MMR differs, sporadic and Lynch syndrome tumors share similar pathological features and have a more favorable stage-adjusted prognosis compared with MMR-proficient cases. While controversy remains, there is evidence to suggest that deficient MMR may predict a lack of benefit from 5-fluorouracil-based adjuvant chemotherapy. The focus of this article is on the MMR phenotype and its prognostic and predictive implications for the management of patients with colorectal cancer.