Traditional Serrated Pathway-associated Colorectal Carcinoma: Morphologic Reappraisal of Serrated Morphology, Tumor Budding, and Identification of Frequent PTEN Alterations

Nonconventional Dysplasia is Frequently Associated With Goblet Cell Deficient and Serrated Variants of Colonic Adenocarcinoma in Inflammatory Bowel Disease

Various subtypes of nonconventional dysplasia have been recently described in inflammatory bowel disease (IBD). We hypothesized that goblet cell deficient dysplasia and serrated dysplasia may be the primary precursor lesions for goblet cell deficient (GCDAC) and serrated (SAC) variants of colonic adenocarcinoma, respectively. Clinicopathologic features of 23 GCDAC and 10 SAC colectomy cases were analyzed. All dysplastic lesions found adjacent to the colorectal cancers (n = 22 for GCDACs and n = 10 for SACs) were subtyped as conventional, nonconventional, or mixed-type dysplasia. As controls, 12 IBD colectomy cases with well to moderately differentiated adenocarcinoma that lacked any mucinous, signet ring cell, low-grade tubuloglandular, or serrated features while retaining goblet cells throughout the tumor (at least 50% of the tumor) were evaluated. The cohort consisted of 19 (58%) men and 14 (42%) women, with a mean age of 53 years and a long history of IBD (mean duration: 18 y). Twenty-seven (82%) patients had ulcerative colitis. GCDACs (57%) were more often flat or invisible than SACs (10%) and controls (25%; P = 0.023). The GCDAC and SAC groups were more likely to show lymphovascular invasion (GCDAC group: 52%, SAC group: 50%, control group: 0%, P = 0.001) and lymph node metastasis (GCDAC group: 39%, SAC group: 50%, control group: 0%, P = 0.009) than the control group. Notably, GCDACs and SACs were more frequently associated with nonconventional dysplasia than controls (GCDAC group: 77%, SAC group: 40%, control group: 0%, P < 0.001). Goblet cell deficient dysplasia (73%) was the most prevalent dysplastic subtype associated with GCDACs ( P = 0.049), whereas dysplasias featuring a serrated component (60%) were most often associated with SACs ( P = 0.001). The GCDAC group (75%) had a higher rate of macroscopically flat or invisible synchronous dysplasia compared with the SAC (20%) and control (33%) groups ( P = 0.045). Synchronous dysplasia demonstrated nonconventional dysplastic features more frequently in the GCDAC (69%) and SAC (40%) groups compared with the control group (0%; P = 0.016). In conclusion, goblet cell deficient dysplasia and dysplasias featuring a serrated component could potentially serve as high-risk markers for GCDACs and SACs, respectively.

Small bowel intussusception caused by a serrated adenoma: a case report

The case was a 17-year-old young woman with a one-year history of recurrent abdominal pain and discomfort. B-scan ultrasonography identified intussusception and contrast-enhanced computed tomography of the pelvis revealed volvulus. A laparoscopic procedure was planned to identify the reason for the intussusception and obstruction. Intraoperatively, the intussusception was found to be caused by a cauliflower-shaped polypoid tumor measuring approximately 4 × 3 cm. Postoperative pathological examination identified the tumor to be a traditional serrated adenoma of the small intestine, which is rare and has atypical clinical manifestations. If unexplained abdominal pain or gastrointestinal bleeding occurs and an abdominal mass cannot be accurately located, laparoscopic or open surgery should be performed immediately. Early surgery is the most effective and reliable way of securing a prompt diagnosis and a favorable prognosis.

Single-cell Transcriptomics Reveals Early Molecular and Immune Alterations Underlying the Serrated Neoplasia Pathway Toward Colorectal Cancer

BACKGROUND & AIMS

Approximately one-third of colorectal cancers develop from serrated lesions (SLs), including hyperplastic polyp (HP), sessile serrated lesion (SSL), traditional serrated adenoma (TSA), and SSL with dysplasia (SSLD) through the serrated neoplasia pathway, which progresses faster than the conventional adenoma-carcinoma pathway. We sought to depict the currently unclarified molecular and immune alterations by the single-cell landscape in SLs.

METHODS

We performed single-cell RNA sequencing of 16 SLs (including 4 proximal HPs, 5 SSLs, 2 SSLDs, and 5 TSAs) vs 3 normal colonic tissues.

RESULTS

A total of 60,568 high-quality cells were obtained. Two distinct epithelial clusters with redox imbalance in SLs were observed, along with upregulation of tumor-promoting SerpinB6 that regulated ROS level. Epithelial clusters of SSL and TSA showed distinct molecular features: SSL-specific epithelium manifested overexpressed proliferative markers with Notch pathway activation, whereas TSA-specific epithelium showed Paneth cell metaplasia with aberrant lysozyme expression. As for immune contexture, enhanced cytotoxic activity of CD8⁺ T cells was observed in SLs; it was mainly attributable to increased proportion of CD103⁺CD8⁺ tissue-resident memory T cells, which might be regulated by retinoic acid metabolism. Microenvironment of SLs was generally immune-activated, whereas some immunosuppressive cells (regulatory T cells, anti-inflammatory macrophages, MDK⁺IgA⁺ plasma cells, MMP11-secreting PDGFRA⁺ fibroblasts) also emerged at early stage and further accumulated in SSLD.

CONCLUSION

Epithelial, immune, and stromal components in the serrated pathway undergo fundamental alterations. Future molecular subtypes of SLs and potential immune therapy might be developed.

Patient-derived organoids identify an apico-basolateral polarity switch associated with survival in colorectal cancer

The metastatic progression of cancer remains a major issue in patient treatment. Yet, the molecular and cellular mechanisms underlying this process remains unclear. Here, we use primary explants and organoids from patients harboring mucinous colorectal carcinoma (MUC CRC), a poor prognosis histological form of digestive cancers, to study the architecture, invasive behavior and chemoresistance of tumor cell intermediates. We report that these tumors maintain a robust apico-basolateral polarity as they spread in the peritumoral stroma or organotypic collagen-I gels. We identified two distinct topologies: MUC CRCs either display a conventional "apical-in" polarity or, more frequently, harbor an inverted "apical-out" topology. Transcriptomic analyses combined with interference experiments on organoids showed that TGFb and focal adhesion signaling pathways are the main drivers of polarity orientation. Finally, this apical-out topology is associated with increased resistance to chemotherapeutic treatments in organoids and decreased patient survival in the clinic. Thus, patient-derived organoids have the potential to bridge histological, cellular and molecular analyses to decrypt onco-morphogenic programs and stratify cancer patients.

Familial Adenomatous Polyposis-associated Traditional Serrated Adenoma of the Small Intestine: A Clinicopathologic and Molecular Analysis

Familial adenomatous polyposis (FAP) is an inherited cancer predisposition syndrome associated with numerous gastrointestinal tract adenomatous polyps, as well as gastric fundic gland polyps and pyloric gland adenomas in the upper gastrointestinal tract. While colonic FAP-associated traditional serrated adenomas (TSAs) have been reported in a few studies, small bowel FAP-associated adenomas with TSA morphology have not been characterized. This study describes the clinicopathologic and molecular findings of this type of adenoma in the small bowel of patients with FAP. We reviewed small bowel adenomas in 45 consecutive FAP patients to identify adenomas with zones showing slit-like serrations, cells with eosinophilic cytoplasm, ectopic crypt formation, and vesicular nuclei. Sporadic small bowel adenomas from 51 consecutive patients were also reviewed for adenomas with the same features. Of the 177 polyps from 45 FAP patients and 60 polyps from 51 nonsyndromic patients, 18 TSAs from 9 FAP patients (20%) and 10 TSAs from the sporadic group (19.6%) were identified. FAP patients presented at a younger age than nonsyndromic patients (median: 43 vs. 66; P=0.0048). FAP-associated TSAs were asymptomatic and smaller than sporadic TSAs (median size: 0.6 vs. 2.5 cm; P=0.00006). Immunostaining for β-catenin and testing for BRAF and KRAS mutations were performed in a subset of the cohort. Nuclear β-catenin was seen in 1 FAP-associated TSA and 3 nonsyndromic TSAs. All TSAs (FAP-associated and nonsyndromic) showed wild-type BRAF, while KRAS mutations were identified only in the nonsyndromic setting. In summary, small bowel FAP-associated and sporadic TSAs share a similar morphology, and the BRAF-serrated pathway does not contribute to their pathogenesis.

Association of PIK3CA mutation and PTEN loss with expression of CD274 (PD-L1) in colorectal carcinoma

Immunotherapy targeting the CD274 (PD-L1)/PDCD1 (PD-1) immune checkpoint axis has emerged as a promising treatment strategy for various cancers. Experimental evidence suggests that phosphatidylinositol-4,5-bisphosphonate 3-kinase (PI3K) signaling may upregulate CD274 expression. Thus, we hypothesized that PIK3CA mutation, PTEN loss, or their combined status might be associated with CD274 overexpression in colorectal carcinoma. We assessed tumor CD274 and PTEN expression by immunohistochemistry and assessed PIK3CA mutation by pyrosequencing in 753 patients among 4,465 incident rectal and colon cancer cases that had occurred in two U.S.-wide prospective cohort studies. To adjust for potential confounders and selection bias due to tissue availability, inverse probability weighted multivariable ordinal logistic regression analyses used the 4,465 cases and tumoral data including microsatellite instability, CpG island methylator phenotype, KRAS and BRAF mutations. PIK3CA mutation and loss of PTEN expression were detected in 111 of 753 cases (15%) and 342 of 585 cases (58%), respectively. Tumor CD274 expression was negative in 306 (41%), low in 195 (26%), and high in 252 (33%) of 753 cases. PTEN loss was associated with CD274 overexpression [multivariable odds ratio (OR) 1.83; 95% confidence interval (CI), 1.22–2.75; P = .004]. PIK3CA mutation was statistically-insignificantly (P = .036 with the stringent alpha level of 0.005) associated with CD274 overexpression (multivariable OR, 1.54; 95% CI, 1.03–2.31). PIK3CA-mutated PTEN-lost tumors (n = 33) showed higher prevalence of CD274-positivity (82%) than PIK3CA-wild-type PTEN-lost tumors (n = 204; 70% CD274-positivity) and PTEN-expressed tumors (n = 147; 50% CD274-positivity) (P = .003). Our findings support the role of PI3K signaling in the CD274/PDCD1 pathway.

Evaluation of Tumor Budding in Primary Colorectal Cancer and Corresponding Liver Metastases Based on H&E and Pancytokeratin Staining

In colorectal cancer, tumor budding is associated with tumor progression and represents an additional prognostic factor in the TNM classification. Tumor buds can be found at the invasive front (peritumoral budding; PTB) and in the tumor center (intratumoral budding; ITB) of primary tumors. Previous studies have shown that tumor buds are also present in colorectal liver metastases (CRLM). Data on the prognostic and predictive role in this clinical context are still sparse and no standardized approach to evaluate budding in CRLM has been published so far. This study aimed to analyze and correlate perimetastatic (PMB) and intrametastatic budding (IMB) on H&E and pancytokeratin staining, compare it to budding results in corresponding primary tumors and to propose a standardized scoring system in CRLM as the basis for future studies. Tumor tissue of 81 primary tumors and 139 corresponding CRLM was used for ngTMA construction. For each primary tumor and metastasis, two punches from the center and two punches from the periphery from areas with highest tumor budding density were included. TMA slides were stained for H&E and pancytokeratin (Pan-CK). PTB, ITB, PMB, and IMB were analyzed and classified as bd1, bd2, and bd3 according to ITBCC guidelines. ITB and PTB as well as IMB and PMB showed significant correlation on H&E and Pan-CK staining. No correlation was found for tumor bud counts in primary tumors and corresponding metastases. The agreement for categorized tumor bud counts showed fair to good agreement for metastases and poor agreement for primary tumors between different classes on H&E and Pan-CK staining. Based on our results, tumor budding in primary tumors and CRLM seems to be different processes which might be the results of differing surrounding microenvironments. The evaluation of tumor budding in CRLM is challenging in cases without desmoplastic stroma reaction or intense perimetastatic ductular reaction. We therefore propose to evaluate tumor budding only in metastases with desmoplastic stroma reaction based on H&E staining since important morphological features are obscured on Pan-CK staining.

The Molecular Hallmarks of the Serrated Pathway in Colorectal Cancer

Colorectal cancer (CRC) is a leading cause of cancer death worldwide. It includes different subtypes that differ in their clinical and prognostic features. In the past decade, in addition to the conventional adenoma-carcinoma model, an alternative multistep mechanism of carcinogenesis, namely the “serrated pathway”, has been described. Approximately, 15 to 30% of all CRCs arise from neoplastic serrated polyps, a heterogeneous group of lesions that are histologically classified into three morphologic categories: hyperplastic polyps, sessile serrated adenomas/polyps, and the traditional serrated adenomas/polyps. Serrated polyps are characterized by genetic (BRAF or KRAS mutations) and epigenetic (CpG island methylator phenotype (CIMP)) alterations that cooperate to initiate and drive malignant transformation from normal colon mucosa to polyps, and then to CRC. The high heterogeneity of the serrated lesions renders their diagnostic and pathological interpretation difficult. Hence, novel genetic and epigenetic biomarkers are required for better classification and management of CRCs. To date, several molecular alterations have been associated with the serrated polyp-CRC sequence. In addition, the gut microbiota is emerging as a contributor to/modulator of the serrated pathway. This review summarizes the state of the art of the genetic, epigenetic and microbiota signatures associated with serrated CRCs, together with their clinical implications.