Multiclonal colorectal cancers with divergent histomorphological features and RAS mutations: one cancer or separate cancers?

Colorectal cancer in patients of advanced age is associated with increased incidence of BRAF p.V600E mutation and mismatch repair deficiency

Introduction

The highest incidence of colorectal cancer (CRC) is in patients diagnosed at 80 years or older highlighting a need for understanding the clinical and molecular features of these tumors. Methods. In this retrospective cohort study, 544 CRCs underwent next generation sequencing and mismatch repair (MMR) evaluation. Molecular and clinical features were compared between 251 patients with traditional-onset CRC (50-69 years at diagnosis) and 60 with late-onset CRC (>80 years at diagnosis).

Results

Late-onset CRC showed a significantly higher rate of right-sided tumors (82% vs 35%), MMR deficiency (35% vs. 8%) and BRAF p.V600E mutations (35% vs. 8%) and a significantly lower rate of stage IV disease (15% vs 28%) and APC mutations (52% vs. 78%). Association of these features with advanced age was supported by stratifying patients into 6 age groups (<40, 40-49, 50-59, 60-69, 70-79 and >80 years). However, the age-related rise in MMR deficient (dMMR) CRC was only seen in the female patients with an incidence of 48% (vs. 10% in the male patient) in the >80y group. In addition, BRAF p.V600E was significantly enriched in MMR deficient CRC of advanced age (67% in late-onset CRC). Categorizing CRC by mutational profiling, late-onset CRC revealed a significantly higher rate of dMMR/BRAF ⁺ APC ^- (18% vs. 2.0%), dMMR/BRAF ^- APC ^- (8.3% vs. 1.2%) and MMR proficient (pMMR)/BRAF ⁺ APC ^- (12% vs. 4.0%) as compared to traditional-onset CRC.

Discussion

In summary, there was a higher rate of dMMR and BRAF p.V600E in late-onset CRC, independently or in combination. The higher incidence of dMMR in late-onset CRC in females is most likely predominantly driven by BRAF p.V600E induced hypermethylation. Prospective studies with treatment plans designed specifically for these older patients are warranted to improve their outcomes.

Genetic and epigenetic dependencies in colorectal cancer development

Recent studies have mapped key genetic changes in colorectal cancer (CRC) that impact important pathways contributing to the multistep models for CRC initiation and development. In parallel with genetic changes, normal and cancer tissues harbor epigenetic alterations impacting regulation of critical genes that have been shown to play profound roles in the tumor initiation. Cumulatively, these molecular changes are only loosely associated with heterogenous transcriptional programs, reflecting the heterogeneity in the various CRC molecular subtypes and the paths to CRC development. Studies from mapping molecular alterations in early CRC lesions and use of experimental models suggest that the intricate dependencies of various genetic and epigenetic hits shape the early development of CRC via different pathways and its manifestation into various CRC subtypes. We highlight the dependency of epigenetic and genetic changes in driving CRC development and discuss factors affecting epigenetic alterations over time and, by extension, risk for cancer.

Double PIK3CA Alterations and Parallel Evolution in Colorectal Cancers

OBJECTIVES

To demonstrate clinicopathologic features and evaluate the clonality of double PIK3CA alterations in colorectal cancers (CRCs).

METHODS

Clonality was examined in 13 CRCs with double PIK3CA alterations (1.7% of CRCs or 9.6% of PIK3CA-mutated CRCs). Multiregional analyses were performed to confirm subclonal PIK3CA alterations.

RESULTS

PIK3CA alterations were detected within exon 9 (51%), exon 20 (23%), exon 1 (15%), and exon 7 (6.0%). CRCs with exon 7 alterations showed a significantly higher incidence of double PIK3CA alterations. Most double PIK3CA alterations consisted of a hotpsot alteration and an uncommon alteration; they were often clonal and present within a single tumor population. Multiregional analyses of CRCs with predicted subclonal double-alterations revealed multiclonal CRCs with divergent PIK3CA variant status originating from a common APC- and KRAS-mutated founder lineage of adenoma.

CONCLUSIONS

The findings supported multiclonal CRCs resulting from parallel evolution during the progression from adenoma to adenocarcinoma within the mitogen-activated protein kinase pathway, as previously demonstrated, or the mammalian target of rapamycin pathway. Further studies are warranted to elucidate clinical significance and potential targeted therapy for CRC patients with double PIK3CA alterations and impacts on clinical decision-making in patients with multiclonal CRCs harboring divergent PIK3CA mutational status.

IDH1 and IDH2 Mutations in Colorectal Cancers

OBJECTIVES

To elucidate clinicopathologic and molecular characteristics of IDH1 and IDH2 (IDH1/2) mutations in colorectal cancers (CRCs).

METHODS

We evaluated IDH1/2 mutations in 1,623 CRCs using a next-generation sequencing assay.

RESULTS

IDH1/2 mutations, predominantly IDH1 p.R132C, were detected in 15 (0.9%) CRCs and in 5 (3.0%) of 167 BRAF p.V600E-mutated CRCs. Three IDH1/2-mutated CRCs were associated with inflammatory bowel disease. They were significantly associated with old age, mucinous or signet ring cell adenocarcinoma, and high-grade histomorphology. Concordance of variant allele frequency between IDH1/2 mutants and other trunk drivers in CRCs and presence of IDH1/2 mutation in the adenoma and early adenocarcinoma indicated IDH1/2 mutations could be trunk drivers suitable for targeted therapy.

CONCLUSIONS

IDH1/2 mutations in CRCs were uncommon but enriched in BRAF p.V600E-mutated CRCs and perhaps colitis-associated CRCs. Further studies on IDH1/2-mutated CRCs are needed to clarify their clinicopathologic features and implications for targeted therapy.