Abstract
INTRODUCTION:
Patients with serrated polyposis syndrome (SPS) have an increased risk to develop colorectal cancer (CRC). Due to an abundance of serrated polyps, these CRCs are assumed to arise mainly through the serrated neoplasia pathway rather than through the classical adenoma-carcinoma pathway. We aimed to evaluate the pathogenetic routes of CRCs in patients with SPS.
METHODS:
We collected endoscopy and pathology data on CRCs and polyps of patients with SPS under treatment in our center. Our primary end point was the proportion of BRAFV600E mutated CRCs, indicating serrated pathway CRCs (sCRCs). CRCs lacking BRAFV600E most likely inferred a classical adenoma-carcinoma origin (aCRCs). We assessed patient, polyp, and CRC characteristics and stratified for BRAFV600E mutation status.
RESULTS:
Thirty-five patients with SPS harbored a total of 43 CRCs. Twenty-one CRCs (48.8%) carried a BRAFV600E mutation, 10 of which lacked MLH1 staining and 17 (81%) were located in the proximal colon. Twenty-two CRCs (51.1%) did not carry a BRAFV600E mutation and were MLH1 proficient. Of these 22 putatively aCRCs, 17 (77.3%) were located distally and one-third (36.4%) harbored a pathogenic KRAS or NRAS mutation. In patients with BRAFwt-CRCs, a higher ratio of the median number of conventional adenomas versus serrated polyps was found (4 vs 13) than patients with BRAFV600E-CRCs (1 vs 14).
DISCUSSION:
Our study indicates that in patients with SPS, the ratio of sCRCs:aCRCs on average is 50:50. This elevated sCRC:aCRC ratio in patients with SPS, when compared with non-SPS patients, correlates well with the differences in the ratios of the numbers of sessile serrated lesions and conventional adenomas in patients with SPS and non-SPS patients, respectively.
KEYWORDS: colorectal cancer, serrated polyposis syndrome, colorectal polyps
INTRODUCTION
Colorectal carcinomas (CRCs) arise from benign precursor lesions, particularly from either conventional adenomas, tubular adenomas (TAs) and tubulovillous adenomas (TVAs), or from the serrated polyp subtypes, i.e. sessile serrated lesions (SSLs) and traditional serrated adenomas (TSAs). The classical adenoma-carcinoma pathway accounts for 70%–80% of all CRCs (1,2) and is ignited by mutations in the Wnt and MAPK pathways, i.e. in KRAS/NRAS and APC genes (3). The serrated neoplasia pathway is responsible for approximately 25% of all sporadic CRCs and are either MLH1 deficient, due to biallelic MLH1 promotor methylation and consequently microsatellite instable (MSI), or MLH1 proficient and microsatellite stable (1,4,5). It is generally assumed that of all serrated polyps, SSLs are the most relevant lesions with the potential to genetically derail and develop into CRC (6,7). This notion is supported by the fact that both SSLs and sporadic microsatellite-instable (MSI) CRCs are typically located in the proximal colon, whereas hyperplastic polyps (HPs) and TSAs are mainly found in the distal colon (3). The earliest known driver mutation of the serrated neoplasia pathway, BRAFV600E, is present in most SSLs and in 75%–90% of sporadic CRCs derived through this pathway (1,4,5,8). Because BRAFV600E is seldom if at all found in classical adenomas nor in Lynch syndrome-related MSI CRCs, the BRAFV600E is considered the most distinguishing marker for serrated polyp–derived CRC (sCRC) (9). BRAFV600E-CRCs are of clinical importance because metastatic BRAFmut-CRCs are known for a poor prognosis with approximately 2-fold increase in mortality rate compared with BRAFwt-CRC (10,11).
Because SSLs have long been largely underdiagnosed, serrated polyposis syndrome (SPS) was formerly considered rare, but now SPS is assumed to be the most prevalent colonic polyp syndrome worldwide (12). SPS is reported to be present in 1:111 individuals participating in CRC screening programs using fecal immunochemical tests and in 1:238 individuals participating in primary colonoscopy screening (13). SPS is characterized by the presence of multiple and/or large serrated polyps throughout the entire colorectum and is associated with an increased CRC risk. Just like the adenoma predominance in patients with familial adenomatous polyposis lead to CRCs of the classical adenoma carcinoma pathway, CRCs in patients with SPS might evolve mainly through the serrated neoplasia pathway. However, conventional adenomas are also detected in 75%–80% of patients with SPS, and almost half of the CRCs are located in the distal colon, the preferential location of conventional adenomas (14,15). In fact, co-occurrence of conventional adenomas in individuals with SPS might lead to a higher CRC risk, as previously suggested (16,17). In a recent study, 11/19 CRCs (58%) detected in patients with SPS were suggested to be derived from conventional adenomas, as indicated by an adjacent conventional adenoma or the presence of an APC/CTNNB1 mutation and a TP53 mutation (18). Also other studies observed the presence of a BRAFV600E in 46%–53% of the CRCs in patients with SPS, suggesting that a proportion of CRCs may not originate from serrated polyps (19,20). Nonetheless, studies that integrate the combination of clinical, pathological, and molecular data of both CRCs and polyps of a nonselected SPS patient cohort are scarce. In a prospectively collected cohort of patients with SPS with CRC, we evaluated the molecular origin of the CRCs in relation to the clinical and endoscopic findings, particularly the number and type of colonic precursor lesions.
METHODS
Study design
This study represents a prospective series of patients diagnosed with SPS under surveillance at the Amsterdam University Medical Centers, as previously described (12). Data regarding patients, polyps, and CRCs were retrieved from colonoscopy and pathology reports. Because patients were not exposed to any additional intervention, this study fell beyond the legislation regarding Medical Research Involving Human Subjects Act. Hence, the medical ethical committee of the Amsterdam University Medical Centers decided that ethical approval was not required for this study. All included patients signed informed consent regarding the use of their pseudonymized data in the general context of research.
Inclusion/exclusion criteria
We included CRCs from patients who fulfilled the criteria of SPS World Health Organization (WHO) 2019 type 1 (5 or more SPs of at least 5 mm located proximal to the rectum, with at least 2 being 10 mm in size) or WHO type 2 (20 or more SPs with at least 5 located proximal to the rectum) (13). All CRCs were revised by an expert pathologist and included only when diagnosed as adenocarcinoma. We excluded a CRC if no tissue was available or if tissue was of insufficient quality for use. CRCs of which a BRAFV600E mutation analysis was previously performed and reported were included regardless of the presence and quality of remnant tissue.
Immunohistochemical staining
Each included formalin-fixed and paraffin-embedded CRC tissue specimen was assessed in a tissue microarray, including 2 control tissues. If the remnant CRC tissue specimen was not sufficient to include in the microarray, slides were stained individually. The microarray was stained for BRAFV600E mouse monoclonal antibody (Roche, VE1), MLH1 (BD Pharmingen, 551092, G168-15), MSH2 (Cell Marque, 286M-16, G219-1129), PMS2 (Cell Marque, 288R-18, EPR3947), MSH6 (Epitomics, AC-0047RUOC, EP49), p53 (ThermoFisher Scientific, DO-7, BP53-12), p16 (Immunologic, ILM 0521-C1, MX007), and SMAD4 (Santa Cruz Biotechnology, sc-7966, B-8). The staining pattern was evaluated and interpreted by an expert GI pathologist.
Gene mutation panel
Next generation sequencing was performed to further characterize BRAFwt-CRCs, using the Ion AmpliSeq Colon Cancer Research Panel v2 (ThermoFisher Scientific, Waltham, MA) for targeted multi-gene amplification. We included for this study hotspots of the following genes: KRAS, NRAS, PIK3CA, SMAD4, and TP53. Libraries were prepared using the ION PGM Hi-Q OT2 Kit, and Ion OneTouch-2 Instrument was used for emulsion PCR and template preparation. The Ion PGM Hi-Q sequencing Kit with the Ion 318 V2 Chip and Personal Genome Machine were used as sequencing platform.
Outcome definitions
Our primary end point was the proportion of CRCs originated from the adenoma carcinoma pathway and serrated neoplasia pathway in patients with SPS. Because a BRAFV600E mutation is the most distinguishable marker, we consider all BRAFV600E-CRCs as derived from SSLs and most BRAFwt-CRCs being derived from conventional adenomas. CRCs were appointed as BRAFV600E-CRC if BRAFV600E staining was positive and BRAFwt-CRC if BRAFV600E staining was negative (see Figure 1).
Figure 1.
Flowchart of included colorectal cancers. AUMC, Amsterdam University Medical Centers; CRC, colorectal cancer; SPS, serrated polyposis syndrome.
Secondary outcome measures were differences in MLH1, p53, and SMAD4 staining between BRAFV600E-CRCs and BRAFwt-CRCs. In addition, the occurrence of gene mutations was evaluated for BRAFwt-CRCs separately using the abovementioned gene mutation panel including 19 potential driver mutations. Clinical characteristics (sex, age at diagnosis) and colonoscopy findings (cancer location, cancer stage, SPS WHO subtype, and the number and type of concomitant polyps) were compared between patients with either BRAFwt-CRC or BRAFV600E-CRC. Cancer stage was classified as advanced and nonadvanced; i.e., advanced-stage CRCs included stage III (metastasis in regional lymph node) or stage IV (metastasis to site or organ) CRCs based on TNM classification (American Joint Committee, eighth edition) (21). Patients with both a BRAFwt-CRC and a BRAFV600E-CRC were excluded for analysis. Advanced adenomas were defined as any adenoma of ≥10 mm, with either tubulovillous or villous architecture and/or containing high-grade dysplasia. Advanced serrated polyps were defined as any serrated polyp ≥10 mm, SSL with dysplasia, or traditional serrated adenoma. Ratios for adenomas to serrated polyps were reported to reflect potential predominance of a polyp subtype.
Statistical analyses
Continuous covariates were presented as median with interquartile range (IQR) in case of non-normal distribution and dichotomous covariates as count with proportion. Median values with decimals were rounded up. Differences in immunohistochemical staining patterns were evaluated using χ2 statistics. Differences in clinical and colonoscopy findings were analyzed using χ2 statistics or Mann-Whitney U statistical test A P value of <0.05 was considered as statistically significant. Analyses were performed using IBM SPSS Statistics 26.
RESULTS
Patient characteristics
From a cohort of 228 patients with SPS, a total of 43 CRCs from 35 patients were included in the study (Figure 1). The median age during SPS diagnosis was 63 years (IQR, 59–69), and 24/35 (68.6%) patients were female individuals (Table 1). In total, 13 (37.1%) patients complied with criteria for SPS WHO type 1, 6 (17.1%) patients complied with criteria for SPS WHO type 2, and 16 (45.7%) patients complied with criteria for SPS both WHO types 1 and 2. As many as 8 patients (22.8%) had a metachronous CRC.
Table 1.
Patient characteristics of all included patients comparing BRAFV600E-CRCs and BRAFwt-CRCs
| Total | BRAFV600E-CRC | BRAFwt-CRC | Serrated CRC + BRAFwt-CRC | P valuea | |
| Total patients; n (%) | 35 (100) | 15 (42.9) | 18 (51.4) | 2 (5.7) | — |
| Female sex; n (%) | 24 (68.6) | 12 (80.0) | 11 (61.1) | 1 (50.0) | 0.710 |
| Patient age of SPS diagnosis; median (IQR) | 63 (58–69) | 63 (60–64) | 64 (58–69.25) | 63 (54–NA) | 0.690 |
| WHO 2019 criteria SPS; n (%) | 0.719 | ||||
| Type 1 | 13 (37.1) | 6 (40.0) | 7 (38.9) | — | 0.379 |
| Type 2 | 6 (17.1) | 1 (6.7) | 5 (27.8) | — | 0.273 |
| Types 1 and 2 | 16 (45.7) | 8 (53.3) | 6 (33.3) | 2 (100) | — |
| Patient with second primary CRC; n (%) | 8 (22.9) | 3 (20.0) | 3 (16.7) | 2 (100) | 0.805 |
CRC, colorectal cancer; SPS, serrated polyposis syndrome; WHO, World Health Organization.
Comparing BRAFV600E-CRC and BRAFwt-CRC with χ2 statistics for categorical variables and Mann-Whitney U test for continuous variables.
Polyp characteristics
In the group of 33 patients with a single CRC, a total of 696 polyps were diagnosed, i.e., 325 HPs (46.7%), 223 SSLs (32.0%), 1 TSA (0.1%), and 138 conventional adenomas (19.8%). In total, 33 patients (100%) had at least 1 SP, 32 patients (97%) had at least 1 HP, 29 patients (87.6%) had at least 1 SSL, 23 (69.7%) patients had at least 1 advanced serrated polyp, and 1 patient (6.7%) had 1 TSA (Table 2). The median number of serrated polyps per patient was 14 (IQR, 7.5–23.5); being 6 (IQR 3.5–15) for HP, 6 (IQR 1.5–9) for SSL, and 0 for TSA. In total, 23 patients (69.7%) had at least 1 adenoma, and 8 patients (24.2%) had at least 1 advanced adenoma. The prevalence of at least 1 TA was 12 (36.7%), at least 1 TVA was 14 (42.4%), and at least 1 villous adenoma was 1 (6.7%). The median number of conventional adenomas per patient was 2 (IQR, 0–6); being 1 (IQR, 0–5) for TA, 0 (0–1.5) for TVA, and 0 for villous adenoma.
Table 2.
Polyp frequency and prevalence in patients with only 1 BRAFV600E-CRCs vs BRAFwt-CRCs
| Total (n = 33) | BRAFV600E-CRC (n = 15) | BRAFwt-CRC (n = 18) | P valuea | |
| Total polyps, median number (IQR) | 17 (10–30) | 17 (14–29) | 19 (10–34) | 0.873 |
| Conventional adenomas, median number (IQR) | 2 (0–6) | 1 (0–5) | 4 (0–10) | 0.401 |
| Tubular adenomas | 1 (0–5) | 1 (0–2) | 3 (0–6.3) | 0.580 |
| Tubulovillous adenomas | 0 (0–1.5) | 0 (0–1) | 1 (0–2) | 0.343 |
| Villous adenomas | 0 | 0 | 0 | 1.000 |
| Advanced adenomas, median number (IQR) | 0 (0–0.5) | 0 (0–1) | 0 (0–0) | 0.401 |
| Serrated polyps, median number (IQR) | 14 (7.5–23.5) | 14 (10–23) | 13 (6.8–25.5) | 0.735 |
| Hyperplastic polyps | 6 (3.5–15) | 6 (4–16) | 6 (2.75–14.5) | 0.682 |
| Sessile serrated lesions | 6 (1.5–9) | 3 (1–8) | 6 (2.5–12.3) | 0.202 |
| Traditional serrated adenomas | 0 | 0 | 0 | 0.762 |
| Advanced serrated polyps, median number (IQR) | 1 (0–3.5) | 1 (0–4) | 2 (0–3.3) | 0.817 |
| At least 1 conventional adenoma | 23 (69.7%) | 11 (73.3%) | 12 (66.7%) | 0.678 |
| Tubular adenomas | 12 (36.4%) | 10 (66.7%) | 11 (61.1%) | 0.741 |
| Tubulovillous adenomas | 14 (42.4%) | 5 (33.3%) | 9 (50%) | 0.335 |
| Villous adenomas | 0 | 0 | 0 | — |
| At least 1 advanced adenomas | 8 (24.2%) | 5 (33.3%) | 3 (16.7%) | 0.317 |
| At least 1 serrated polyp | 33 (100%) | 15 (100%) | 18 (100%) | 0.354 |
| Hyperplastic polyps | 32 (97.0%) | 15 (100%) | 17 (94.4%) | 0.570 |
| Sessile serrated lesions | 29 (87.9%) | 13 (86.7%) | 16 (88.9%) | 0.846 |
| Traditional serrated adenomas | 1 (3.0%) | 1 (6.7%) | 0 | 0.266 |
| At least 1 advanced serrated polyp | 21 (63.6%) | 11 (73.3%) | 10 (55.6%) | 0.290 |
CRC, colorectal cancer; IQR, interquartile range.
Comparing BRAFV600E-CRC and BRAFwt-CRC with Mann-Whitney U test.
In the group of 8 patients with 2 CRCs (Table 3), the median number of any polyps was 22 (IQR, 8.5–24.0); being 5.0 (0.5–8.8) for conventional adenomas, 15.0 (3.8–17.5) for serrated polyps, 5.0 (1.0–8.3) for SSLs, 0 (0–1.0) for advanced adenomas, and 3.0 (0.0–5.5) for advanced serrated polyps.
Table 3.
Polyp frequency and prevalence in patients with metachronous CRC
| Total | Second BRAFV600E-CRC | Second BRAFwt-CRC | Serrated CRC + BRAFwt-CRC | |
| Patients, n | 8 | 3 | 3 | 2 |
| Total polyps, median number (IQR) | 22 (8.5–24.0) | 17.7 (14.7) | 14.0 (8.7) | 22.0 (2.8) |
| Conventional adenomas, median number (IQR)/mean (SD)a | 5.0 (0.5–9.5) | 4.3 (7.5) | 6.3 (3.2) | 5 (4.2) |
| Tubular adenomas | 4.0 (0.5–8.8) | 4.0 (6.9) | 5.3 (3.2) | 5 (4.2) |
| Tubulovillous adenomas | 1.0 (0–1.0) | 0.3 (0.6) | 1.0 (0) | 0 |
| Villous adenomas | 0 | 0 | 0 | 0 |
| Advanced adenomas, median number (IQR)/mean (SD) | 0 (0–1.0) | 0.3 (0.6) | 0.3 (0.6) | 0.5 (0.7) |
| Serrated polyps, median number (IQR)/mean (SD) | 15.0 (3.8–17.5) | 13.3 (11.2) | 7.6 (5.7) | 17.0 (1.4) |
| Hyperplastic polyps | 4.0 (1.3–9.8) | 9.3 (11.1) | 2.7 (3.1) | 6.5 (6.4) |
| Sessile serrated lesions | 5.0 (1.0–8.3) | 3.3 (4.9) | 4.3 (2.9) | 8.0 (7.1) |
| Traditional serrated adenomas | 0 | 0 (0) | 0 | 0 |
| Advanced serrated polyps, median number (IQR)/mean (SD) | 3.0 (0.0–5.5) | 3.7 (3.5) | 1 (1.7) | 4.5 (2.1) |
| At least 1 conventional adenoma | 6 (75.0) | 1 (33.3) | 3 (100) | 2 (100) |
| Tubular adenomas | 6 (75.0) | 1 (33.3) | 3 (100) | 2 (100) |
| Tubulovillous adenomas | 4 (50.0) | 1 (33.3) | 3 (100) | 0 |
| Villous adenomas | 0 | 0 | 0 | 0 |
| At least 1 advanced adenomas | 3 (37.5) | 1 (33.3) | 1 (33.3) | 1 (50.0) |
| At least 1 serrated polyp | 8 (100) | 3 (100) | 3 (100) | 2 (100) |
| Hyperplastic polyps | 7 (87.5) | 3 (100) | 2 (66.7) | 2 (100) |
| Sessile serrated lesions | 7 (87.5) | 2 (66.7) | 3 (100) | 2 (100) |
| Traditional serrated adenomas | 0 | 0 | 0 | 0 |
| At least 1 advanced serrated polyp | 5 (62.5) | 2 (66.7) | 1 (33.3) | 2 (100) |
CRC, colorectal cancer; IQR, interquartile range.
Low frequencies were presented in mean with SD.
Primary outcome: BRAFV600E or BRAFwt colorectal cancer?
Of all CRCs, 22/43 (51.2%) were classified as BRAFwt and 21/43 (48.8%) were BRAFV600E (Table 4). Of all patients, the first CRC was classified as BRAFV600E in 15/35 (42.9%), as BRAFwt in 18/35 (51.4%), and synchronous BRAFV600E and BRAFwt in 2/35 (5.7%). Among the 8 patients who had a metachronous CRC, 3 had 2 BRAFV600E-CRCs, 3 had 2 BRAFwt-CRCs, and 2 patients had a combination of a BRAFV600E-CRC and a BRAFwt-CRC (Table 3).
Table 4.
Colorectal cancer characteristics comparing BRAFV600E-CRCs and BRAFwt-CRCs
| Total | BRAFV600E-CRC | BRAFwt-CRC | P valuea | |
| Cohort size; n (%) | 43 (100) | 21 (48.8) | 22 (51.2) | |
| CRC location; n (%) | <0.001 | |||
| Proximal | 22 (51.2) | 17 (81.0) | 5 (22.7) | |
| Distal | 21 (48.8) | 4 (19.0) | 17 (77.3) | |
| Median CRC diameter in mm; n (range) | 32.5 (16.8–51.2) | 35 (15.5–55) | 25 (20–50) | .820 |
| Tumor stage; n (%) | .586 | |||
| Nonadvanced | 29 (67.4) | 15 (71.4) | 14 (63.6) | |
| Advanced | 14 (32.6) | 6 (28.6) | 8 (36.4) | |
| MLH1 expression loss; n (% of cohort) | 10 (23.2) | 10 (47.6) | 0 | <0.001 |
| PMS2 expression loss; n (% of cohort) | 10 (23.2) | 10 (47.6) | 0 | <0.001 |
| MSH2 expression loss | 0 | 0 | 0 | NA |
| MSH6 expression loss | 0 | 0 | 0 | NA |
| SMAD4 expression loss | 4 | 2 (9.5) | 2 (9.1) | 1.000 |
| p53 overexpression/loss of expressionb | 22 | 9 (42.9) | 17 (77.3) | 0.475 |
| MLH1 deficient | 1 (33.3) | 1 (4.8) | 0 | |
| MLH1 proficient | 21 (66.7) | 8 (38.1) | 17 (77.3) | |
| p16 expression loss | 2 | 2 (9.5) | 0 | 0.163 |
| RAS mutation | NA | NA | 8 (36.4) | NA |
| KRAS | 7 (31.8) | |||
| NRAS | 1 (4.5) | |||
| TP53 mutation | NA | NA | 9 (40.9) | NA |
| PIK3CA mutation | NA | NA | 4 (18.2) | NA |
| SMAD4 mutation | NA | NA | 2 (9.1) | NA |
CRC, colorectal cancer; IQR, interquartile range.
Comparing BRAFV600E-CRC and BRAFwt-CRC with χ2 statistics for categorical variables and Mann-Whitney U test for continuous variables.
Based on 34 CRCs.
Secondary outcomes: differences between BRAFV600E or BRAFwt colorectal cancer
Comparing patients with BRAFV600E-CRC (n = 15) and patients with BRAFwt-CRC (n = 18), no differences were found in the ratio of female patients vs male patients (80.0% vs 61.1%, P = 0.710), median age (63 [60–64] vs 64 [58–69.25]) and compliance with criteria of WHO type 1 (40.0% vs 38.9%, P = 0.379) or WHO type 2 (6.7% vs 27.8%, P = 0.273) (Table 1).
BRAFwt-CRCs were more frequently located in the distal colon as opposed to BRAFV600E-CRC (77.3% vs 19.0%, P < 0.001). BRAFwt-CRCs had a nonadvanced stage in 14 (63.6%) cases, when compared with 15 (71.4%) BRAFV600E-CRCs (P = 0.586).
MLH1 and PMS2 expression loss were found in the 10/21 BRAFV600E-CRCs and not in BRAFwt-CRCs (47.6% vs 0%, P < 0.001) (Table 4 and Figure 2). Other gene products (MSH2, MSH6, SMAD4, p53 and p16) showed no statistical differences. Additional mutation analyses of 22 BRAFwt-CRC demonstrated mutations in KRAS in 7 (31.8%), NRAS in 1 (4.5%), PIK3CA in 4 (18.2%), SMAD4 in 2 (9.1%), and TP53 mutation in 9 (40.9%) CRCs.
Figure 2.
Two prototypic colorectal cancer types in patients with serrated polyposis syndrome. Upper and lower panels depict an MSS CRC and an MSI CRC, respectively, both stained (from left to right) for hematoxylin and eosin, BRAFV600E, MLH1, and PMS2. Note that the MSS CRC shows coexpression of MLH1 and PMS2 and lacks staining for BRAFV600E, while the MSI CRC expresses BRAFV600E and lacks nuclear staining for MLH1 and PMS2 (only the neighboring stromal and inflammatory cells are MLH1 and PMS2 positive). MSI, microsatellite instable; MSS, microsatellite stable.
No significant statistical differences were found regarding the prevalence and frequency of polyp subtypes between both groups (Table 2). Nonetheless, we observed that patients with BRAFwt-CRCs had a higher median number of conventional adenomas (4.0 [IQR, 0–10] vs 1.0 [IQR, 0–5], P = 0.401) when compared with patients with BRAFV600E-CRCs. Patients with BRAFV600E-CRCs had a median number of 14 (10–23) serrated polyps against a median of 13 (6.8–25.5, P = 0.735) for patients with BRAFwt-CRC. The ratio of serrated polyp to adenoma was lower in patients with BRAFwt-CRC (4:1) than in patients with BRAFV600E-CRC (14:1, P = 0.059).
In addition, no significant differences were found comparing patients with 2 metachronous CRCs (Table 3). Three patients with 2 BRAFV600E-CRCs had a mean of 4.3 (SD, 7.5) conventional adenomas, 13.3 (11.2) serrated polyps, 3.3 (4.9) SSLs, 4.3 (7.5) advanced adenomas, and 3.7 (3.5) advanced serrated polyps. Three patients with 2 BRAFwt-CRCs had a mean of 6.3 (SD 3.2) conventional adenomas, 7.6 (5.7) serrated polyps, 4.3 (2.9) SSLs, 6.3 (3.2) advanced adenomas, and 1 (1.7) advanced serrated polyp.
DISCUSSION
Our study on 43 CRCs from 35 patients with SPS demonstrated that half of the CRCs were BRAFV600E(48.8%) and originated from the serrated neoplasia pathway (sCRC) and half were BRAFwt (51.1%) most likely evolved through the classical adenoma-carcinoma pathway. A statistically nonsignificant observation was that within this limited cohort, patients with BRAFwt-CRC had proportionally more conventional adenomas than patients with BRAFV600E-CRC, suggesting a relatively adenoma-rich phenotype in the adenoma-carcinoma pathway group.
The 48.8 percent sCRC is considerably higher than the 13 percent sCRCs reported in age-matched patients in publicly available datasets (22). As many as 17 (81%) BRAFV600E-CRCs were located in the proximal colon, consistent with previous studies from both general risk populations and SPS cohorts (4,5,20). Approximately half of the CRCs likely originate from the classical adenoma-carcinoma pathway, i.e., 22/43 CRCs (49%) are BRAFwt and MLH1 proficient and predominantly (77.3%) located in the distal colon. Moreover, in approximately one-third of BRAFwt-CRCs, pathogenic KRAS (31.8%) or NRAS (4.5%) mutations were demonstrated, which is largely concordant with RAS mutation frequencies reported in large CRC cohorts (23–25). It is noteworthy that all our BRAFV600E-CRCs are MLH1 deficient because in a series of sporadic, MLH1-methylated MSI CRCs, 10%–25% lack a BRAF mutation. The fact that no BRAF mutations are present in the 22 MLH1 proficient CRCs does not fully exclude descent from an SSL; statistically, 1 or a few of these 22 microsatellite stable CRCs might originate from a BRAFwt-SSL. In addition, the heterogeneous genetic makeup of BRAFwt-CRCs (Table 4) does not contribute either in defining the potential precursor lesions.
We did not identify a statistically significant difference in total polyp burden between patients with BRAFV600E-CRCs and BRAFwt-CRCs. We did observe some interesting findings within our cohort of patients with SPS with CRC. The prevalence of serrated polyps was higher than that of conventional adenomas (100% vs 69.7%). In addition, the median number of serrated polyps outnumbers those of conventional adenomas and compares as 7:1. This ratio was lower in patients with BRAFwt-CRCs (4:1) than in patients with BRAFV600E-CRC (14:1, P = 0.059). Studies on larger cohorts are needed to substantiate these observations.
BRAFV600E was present in almost half of all included CRCs (48.8%). The proportion we found was in line with a meta-analysis including 4 SPS cohorts (49%) (26). Another recent study reported a lower proportion of BRAFV600E-CRCs (27.8%) (18); however, this regarded a cohort in Japan where a lower incidence of BRAFV600E-CRC in the general population has been described (27). In addition, the authors applied different outcome definitions to classify sCRCs, thus limiting further comparison.
For the interpretation of our results, some limitations have to be accounted for. Because our study population largely consisted of female patients, our results may not necessarily be translated to male patients. It is noted that our nonselected SPS patient cohort still is relatively large when compared with SPS cohorts in other expertise centers. As mentioned, our annotation of sCRC and aCRC solely based on the presence of a BRAFV600E mutation clearly is a simplified representation of carcinogenesis. We feel that this simplification is defensible, and in our view, there is as yet no better way to distinguish both cancer subtypes so far.
Collectively, our cohort of 35 patients with SPS accumulated a total of 696 endoscopically removed colonic polyps including 223 SSLs and 138 conventional adenomas. This infers an average of 6.4 SSLs and 3.9 conventional adenomas per patient with SPS, which roughly is a 4-time and 2-time increased burden of SSLs and conventional adenomas, respectively, when compared with general age-matched populations (3%–31%) (28,29). In unselected cohorts of patients with CRC (aged 66–67 years), the relative contribution of classical CRCs and sCRCs is 70%–75% and 25%–30%, respectively (ratio 2.3–3) (1,2). Within our SPS patient cohort, the relative share of sCRCs is roughly doubled to 50% (21/43 BRAFV600E), which relates remarkably well with the extent of the above-described SSL/adenoma ratio shift in this cohort. Another indication that colorectal carcinogenesis in patients with SPS might be essentially similar to that in the general population is the age at which patients are being diagnosed with CRC. Because SPS is mostly diagnosed during CRC diagnosis (30), the median age of SPS diagnosis in our cohort (63 years) was comparable with the median age of CRC diagnosis in the general population (66–67 years) (31,32). Our findings thus point toward a sheer stochastic process of colorectal carcinogenesis of the 2 types of potential precursor lesions, alike in patients with SPS and non-SPS patients. It also suggests that SSLs from patients with SPS are not more prone to derail and are biologically not different from sporadic SSLs in non-SPS individuals.
CONFLICTS OF INTEREST
Guarantor of the article: Carel J. M. van Noesel, MD, PhD.
Specific author contributions: D.E.F.W.M.v.T., J.E.G.IJ., and C.J.M.v.N. planned and conducted the study. D.E.F.W.M.v.T., H.B., A.R.M. collected the data. All authors interpreted the data, all authors drafted the manuscript, and all authors approved submission.
Financial support: None to report.
Potential competing interests: E.D. received a research grant from FujiFilm, a consulting fee for medical advice from Tillots, Olympus, Fujifilm, GI Supply, CPP-FAP, PAION, and Ambu, and a speakers' fee from Olympus, GI Supply, Norgine, IPSEN, PAION, and Fujifilm. All other authors have nothing to disclose.
Study Highlights.
WHAT IS KNOWN
✓ Serrated polyposis is associated with an increased risk of colorectal cancer.
✓ Cancers are believed to arise mainly through the serrated neoplasia pathway because of serrated polyp abundance.
✓ However, the adenoma-carcinoma pathway seems to play an important role as well.
WHAT IS NEW HERE
✓ Half of all cancers in the context of serrated polyposis syndrome originate from the serrated neoplasia pathway.
✓ The ratio of sessile serrated lesions versus conventional adenomas seems to predict the serrated derived colorectal cancer development.
✓ Colorectal carcinogenesis in patients with serrated polyposis seems not to differ from that in average risk patients.
Contributor Information
David E. F. W. M. van Toledo, Email: d.e.vantoledo@amsterdamumc.nl.
Joep E.G. IJspeert, Email: j.e.ijspeert@amsterdamumc.nl.
Hannah Boersma, Email: h.boersma@amsterdamumc.nl.
Alex R. Musler, Email: a.r.musler@amsterdamumc.nl.
Arne G. C. Bleijenberg, Email: a.g.bleijenberg@amsterdamumc.nl.
Evelien Dekker, Email: e.dekker@amsterdamumc.nl.
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