Natural history of colorectal nonpolypoid adenomas: a prospective colonoscopic study and relation with cell kinetics and K-ras mutations

Incidence of Advanced Colorectal Neoplasia in Individuals With Untreated Diminutive Colorectal Adenomas Diagnosed by Magnifying Image-Enhanced Endoscopy

OBJECTIVES

Because of the increasing number of detected diminutive colorectal adenomas, the "diagnose-and-do-not-resect" approach has recently attracted attention as an alternative to resection. We evaluated the cumulative incidence of advanced colorectal neoplasia (ACN) in individuals with untreated diminutive adenomas and compared this incidence in individuals without adenomas.

METHODS

Data from 1,378 individuals who underwent first screening colonoscopy (CS) and at least one follow-up CS without polypectomy were analyzed. Patients with no adenomas or with only nonadvanced diminutive adenomas (<5 mm) diagnosed by magnifying image-enhanced endoscopy were scheduled to undergo a follow-up CS within 5 years after the initial CS without treatment. The participants were divided into 2 groups: those with untreated diminutive adenomas (group A) and those with no adenomas (group B). The cumulative incidence of ACN and the hazard ratio were assessed using Gray's test and the Fine and Gray model.

RESULTS

During the median follow-up period of 60.9 months, 21 ACNs were detected. The 5-year cumulative incidences of ACN in group A (n = 361) and group B (n = 1,017) were 1.4% (95% confidence interval [CI]: 0.5-3.4) and 0.8% (95% CI: 0.3-1.7), respectively, without a statistically significant difference (P = 0.23). No ACNs developed from unresected adenomas. The smoking status was significantly associated with the incidence of ACN, and the hazard ratio for ACN in group A vs group B adjusted for smoking status was 1.43 (95% CI: 0.52-3.90; P = 0.48).

DISCUSSION

The low 5-year cumulative incidence of ACN suggests the potential to adopt the "diagnose-and-do-not-resect" strategy as an alternative option for diminutive adenomas not requiring excessive surveillance.

Natural history of diminutive and small colorectal polyps: a systematic literature review

BACKGROUND AND AIMS

Diminutive (1-5 mm) and small (6-9 mm) polyps comprise 90% of detected lesions during colonoscopy and rarely contain advanced histology or colorectal cancer (CRC). Routine removal of these lesions results in a significant burden to colonoscopy programs. At the same time, the risk for progression of these polyps to CRC is unclear. We performed a systematic review to explore the natural history of diminutive and small colorectal polyps.

METHODS

We searched MEDLINE and EMBASE for studies investigating the natural history of colorectal polyps. Studies were considered eligible when they assessed patients with 1- to 9-mm polyps that were not treated with polypectomy and that underwent follow-up. We excluded studies in patients with inflammatory bowel disease, polyposis syndromes, and previously diagnosed CRC. We independently extracted study characteristics and evaluated CRC and advanced adenoma (size ≥ 10 mm, containing high-grade dysplasia or villous features) as outcome parameters.

RESULTS

Of 8775 retrieved studies, 9 studies with 721 patients were included that prospectively evaluated the evolution of 1- to 9-mm polyps. In 7 studies the average duration of observation was 2 to 3 years. There was only 1 study in which 1 small polyp might have progressed to cancer. Of 1034 adenomas sized 1 to 9 mm in those studies, 6% progressed to advanced adenomas over time.

CONCLUSIONS

Based on this systematic review, it appears that some 1- to 9-mm adenomas progress to advanced adenomas within 2 to 3 years. No information on long-term CRC transition rates was found. Defining the biologic significance of these polyps is needed to balance between benefits and harm of polypectomy. (PROSPERO database registration number: CRD42016036577.).

Development and progression of colorectal cancer based on follow-up analysis

Elucidating the pathway of colorectal cancer development and progression can lead to identification of lesions that must be treated appropriately. The aim of the present review was to summarize the development and progression of colorectal cancer based on radiological and endoscopic follow-up analyses. These studies revealed several characteristic findings, including that initial morphology with progression to advanced cancer was most commonly 0-Is, followed by 0-IIa. Based on the doubling time, 0-Ip grew slowly in comparison with other morphologies. The observation period from adenomas measuring <10 mm to intramucosal cancers was more than 5 years. This makes it difficult to draw any accurate conclusions about the natural history of colorectal cancer based on follow-up observation alone and it is difficult to exclude the selection bias because of the difficulty of follow up for flat and depressed tumor. However, the only reliable way to elucidate the natural history is to accumulate cases.

Methylation epigenotypes and genetic features in colorectal laterally spreading tumors

Aberrant DNA methylation plays an important role in genesis of colorectal cancer (CRC). Previously, we identified Group 1 and Group 2 methylation markers through genome-wide DNA methylation analysis, and classified CRC and protruded adenoma into three distinct clusters: high-, intermediate- and low-methylation epigenotypes. High-methylation epigenotype strongly correlated with BRAF mutations and these aberrations were involved in the serrated pathway, whereas intermediate-methylation epigenotype strongly correlated with KRAS mutations. Here, we investigated laterally spreading tumors (LSTs), which are flat, early CRC lesions, through quantitative methylation analysis of six Group 1 and 14 Group 2 methylation markers using pyrosequencing. Gene mutations in BRAF, KRAS and PIK3CA, and immunostaining of TP53 and CTNNB1 as well as other clinicopathological factors were also evaluated. By hierarchical clustering using methylation information, LSTs were classified into two subtypes; intermediate-methylation epigenotype correlating with KRAS mutations (p = 9 × 10(-4)) and a granular morphology (LST-G) (p = 1 × 10(-7)), and low-methylation epigenotype correlating with CTNNB1 activation (p = 0.002) and a nongranular morphology (LST-NG) (p = 1 × 10(-7)). Group 1 marker methylation and BRAF mutations were barely detected, suggesting that high-methylation epigenotype was unlikely to be involved in LST development. TP53 mutations correlated significantly with malignant transformation, regardless of epigenotype or morphology type. Together, this may suggest that two molecular pathways, intermediate methylation associated with KRAS mutations and LST-G morphology, and low methylation associated with CTNNB1 activation and LST-NG morphology, might be involved in LST development, and that involvement of TP53 mutations could be important in both subtypes in the development from adenoma to cancer.

Accumulation of aberrant DNA methylation during colorectal cancer development

Despite the recent advances in the therapeutic modalities, colorectal cancer (CRC) remains to be one of the most common causes of cancer-related death. CRC arises through accumulation of multiple genetic and epigenetic alterations that transform normal colonic epithelium into adenocarcinomas. Among crucial roles of epigenetic alterations, gene silencing by aberrant DNA methylation of promoter regions is one of the most important epigenetic mechanisms. Recent comprehensive methylation analyses on genome-wide scale revealed that sporadic CRC can be classified into distinct epigenotypes. Each epigenotype cooperates with specific genetic alterations, suggesting that they represent different molecular carcinogenic pathways. Precursor lesions of CRC, such as conventional and serrated adenomas, already show similar methylation accumulation to CRC, and can therefore be classified into those epigenotypes of CRC. In addition, specific DNA methylation already occurs in the normal colonic mucosa, which might be utilized for prediction of the personal CRC risk. DNA methylation is suggested to occur at an earlier stage than carcinoma formation, and may predict the molecular basis for future development of CRC. Here, we review DNA methylation and CRC classification, and discuss the possible clinical usefulness of DNA methylation as biomarkers for the diagnosis, prediction of the prognosis and the response to therapy of CRC.

Tracking the molecular features of nonpolypoid colorectal neoplasms: a systematic review and meta-analysis

OBJECTIVES

Nonpolypoid colorectal neoplasms (NP-CRNs) are proposed as a major contributor to the occurrence of interval cancers, but their underlying biology remains controversial. We conducted a systematic review and meta-analysis to clarify the major biological events in NP-CRNs.

METHODS

We systematically searched for studies examining molecular characteristics of NP-CRNs. We performed random effect meta-analyses. We measured the heterogeneity among studies using I(2) and possible publication bias using funnel plots.

RESULTS

Fifty-three studies on KRAS, APC, or BRAF mutations, microsatellite instability (MSI), CpG island methylator phenotype (CIMP), or DNA promoter hypermethylation were included. We observed less KRAS mutations (summary odds ratio (OR) 0.30, confidence interval (CI)=0.19-0.46, I(2)=77.4%, CI=70.1-82.9) and APC mutations (summary OR 0.42, CI=0.24-0.72, I(2)=22.6%, CI=0.0-66.7) in NP-CRNs vs. protruded CRNs, whereas BRAF mutations were more frequent (summary OR 2.20, CI=1.01-4.81, I(2)=0%, CI=0-70.8), albeit all with large heterogeneity. Less KRAS mutations were especially found in NP-CRNs subtypes: depressed CRNs (summary OR 0.12, CI=0.05-0.29, I(2)=0%, CI=0-67.6), non-granular lateral spreading tumors (LSTs-NG) (summary OR 0.61, CI=0.37-1.0, I(2)=0%, CI=0-74.6), and early nonpolypoid carcinomas (summary OR 0.11, CI=0.06-0.19, I(2)=0%, CI=0-58.3). MSI frequency was similar in NP-CRNs and protruded CRNs (summary OR 0.99, CI=0.21-4.71, I(2)=70.3%, CI=38.4-85.7). Data for promoter hypermethylation and CIMP were inconsistent, precluding meaningful conclusions.

CONCLUSIONS

This meta-analysis provides indications that NP-CRNs are molecularly different from protruded CRNs. In particular, some subtypes of NP-CRNs, the depressed and LST-NG, are featured by less KRAS mutations than polypoid CRNs. Prospective, multicenter studies are needed to clarify the molecular pathways underlying nonpolypoid colorectal carcinogenesis and potential implications for surveillance intervals.

The natural history of non-polypoid colorectal neoplasms

Despite their importance, little is known about the natural history of non-polypoid colorectal neoplasms (NP-CRN). This article will summarize the available data to gain some estimates of the natural history of NP-CRN.

Comparison of the clinicopathologic features between flat and polypoid adenoma

OBJECTIVE

Several reports have suggested that flat colorectal adenomas might exhibit a higher potential for malignancy compared to polypoid adenomas. Although the clinical importance of the shape of polyps is stressed, the controversy surrounding the malignant potential of flat adenomas continues. The aim of this study was to compare the clinicopathologic characteristics, including degree of dysplasia and malignancy, between flat and polypoid adenomas 5 mm in size or larger.

MATERIAL AND METHODS

A total of 3263 polyps (254 flat adenomas and 3009 polypoid adenomas), >/=5 mm in size, diagnosed in 1883 patients by colonoscopy were analyzed.

RESULTS

Flat adenomas were found in 10% of patients, which represented 7.8% of all adenomas removed. The flat adenomas were larger in diameter than the polypoid adenomas (14.8+/-12.6 mm versus 8.6+/-5.0 mm, p <0.01), had a higher rate of villous components (18.5% versus 11.4%, p <0.01), a higher rate of high-grade dysplasia (9.4% versus 4.2%, p <0.01), and a higher rate of malignancy (10.2% versus 3.6%, p <0.01) than polypoid adenomas. However, there was no difference in the rate of high-grade dysplasia or carcinoma between flat and polypoid adenomas of equal size. It was shown by multivariate analysis that rectosigmoid location, larger size, and presence of a villous component were associated with a higher rate of malignancy, but not with flat morphology.

CONCLUSIONS

Flat adenomas, which were of a relatively large size in this study, were not associated with a higher risk for high-grade dysplasia and carcinoma compared with polypoid adenomas.

K-ras mutations and cell kinetics in Helicobacter pylori associated gastric intestinal metaplasia: a comparison before and after eradication in patients with chronic gastritis and gastric cancer

BACKGROUND

Helicobacter pylori related gastric intestinal metaplasia (IM) is considered to be a precancerous lesion.

AIMS

To identify the effects of H pylori eradication on K-ras mutations, cell kinetics in IM and histological changes in patients with and without gastric cancers in a one-year prospective study.

METHODS

Patients included group A (n = 39), chronic gastritis, and group B (n = 53), intestinal-type early gastric cancer patients who had all undergone endoscopic mucosal resection (n = 25) or surgical resection (n = 28). K-ras codon 12 mutations in IM were examined, followed by DNA sequencing analysis. Proliferating and apoptotic cells were detected with anti-Ki-67 antibody and using the TUNEL method, respectively.

RESULTS

The incidence of K-ras mutations in the cancer was only 3.8%. The mutant K-ras in IM was observed more frequently in group A (46.2%) than in group B patients (1.9%) (p<0.005). After eradication, the K-ras mutations significantly declined to 12.8% in group A (p<0.005). The mutation pattern of K-ras codon 12 before eradication was that GGT was mainly changed to AGT (50%) in group A. AGT transformation was not affected by treatment. Apoptosis in IM showed an increase after H pylori eradication in both groups (p<0.05 in group A) although no histological improvement in IM was observed. The monocyte score was significantly higher in group A than in group B (p<0.05); the score improved significantly after eradication.

CONCLUSIONS

K-ras mutations in IM do not always play a role in gastric carcinogenesis but cell kinetics, especially apoptosis, in IM may contribute to it. There are early events in K-ras mutations which are influenced by H pylori infection; some mutations may also be selected by eradication. These unstable K-ras mutations in IM may be related to lymphocyte infiltration caused by H pylori infection.

PERFORMING A COLONOSCOPY 12 MONTHS AFTER SURGERY FOR COLORECTAL NEOPLASIA

BACKGROUND

There appears to be acceptance that following up patients after surgery for colorectal neoplasia is of value. However, specific issues relating to which investigations to perform and how often remain unresolved. The aim of this project was to evaluate the clinical utility of performing a colonoscopy 12 months after curative surgery for colorectal neoplasia.

METHODS

Patients were selected if they had undergone a curative resection for colorectal neoplasia, and if they had had a completed colonoscopy prior to surgery. Study endpoints included: (i) compliance with follow up; (ii) the prevalence, total number, size, and histology of polyps; and (iii) identification of recurrent or metachronous cancer.

RESULTS

The study group included 253 patients of mean age 69.7 years (SD 11.6) and a male : female ratio of 1.4:1.0. Colonoscopies were completed on 90% of patients at a mean of 1.1 years following surgery. A total of 149 polyps were identified in 30% of patients. On histology, 42% were tubular adenomas, 6% tubulo-villous adenomas, 7% were villous adenomas, and 37% were hyperplastic. Advanced adenomas were identified in 7.9% of patients (95% CI 4.8-12.1%). No recurrent or metachronous cancers were identified.

CONCLUSION

We have observed a high prevalence of advanced adenomas in patients undergoing a 12-month, follow-up colonoscopy after curative surgery for colorectal neoplasia. The significance of these observations requires further evaluation.