Correlation between microsatellite instability status and grading assessed by the counting of poorly differentiated clusters in colorectal cancer

Poorly differentiated clusters in colorectal cancer: a current review and implications for future practice

Poorly differentiated clusters (PDC), defined as small groups of ≥5 tumour cells without glandular differentiation, have gained recent attention as a promising prognostic factor in colorectal cancer (CRC). Numerous studies have shown PDC to be significantly associated with other adverse histopathological features and worse clinical outcomes. PDC may hold particular promise in stage II colon cancer, where risk stratification plays a critical role in patient selection for adjuvant chemotherapy. In addition, emerging evidence suggests that PDC can predict lymph node metastasis in endoscopically resected pT1 CRC, potentially helping the selection of patients for oncological resection. In 'head-to-head' comparisons, PDC grade has consistently outperformed conventional histological grading systems both in terms of risk stratification and reproducibility. With a number of large-scale studies now available, this review evaluates the evidence regarding the prognostic significance of PDC, considers its relationship with other emerging invasive front prognostic markers (such as tumour budding and stroma type), assesses its 'practice readiness', addressing issues such as interobserver reproducibility, scoring methodologies and special histological subtypes (e.g. micropapillary and mucinous carcinoma), and draws attention to ongoing challenges and areas in need of further study. Finally, emerging data on the role of PDC in non-colorectal cancers are briefly considered.

KRAS, NRAS, BRAF mutations and high counts of poorly differentiated clusters of neoplastic cells in colorectal cancer: observational analysis of 175 cases

A novel grading system based on the counting of poorly differentiated clusters (PDC) of neoplastic cells at the invasive margin and in the tumour stroma was recently introduced among the histological parameters predictive of adverse clinical outcome in colorectal cancer (CRC). The aim of this study was to correlate the histological grade based on PDC and the mutational status of KRAS, NRAS and BRAF genes in 175 consecutive CRCs. The highest PDC count under the objective lens of a ×20 microscopic field in each tumour was considered for grading assessment, so that PDC counts <5, 5-9 and ≥10 PDCs were defined grade 1, grade 2 and grade 3, respectively. Hotspots mutations were identified using the MassArray platform. Overall, there were 42 (24%) mutated tumours. Mutational status was significantly associated with high pT stage (p = 0.0021), advanced pTNM stage (p = 0.0018), nodal metastases (p = 0.006), tumour budding (p = 0.022) and high PDC grade (p = 0.0022). KRAS mutations were significantly associated with PDC grade (p = 0.0379), while BRAF mutations were associated with PDC-G3 although statistical significance was not reached. No significant associations were found between NRAS and PDC. The significant association between mutated KRAS and PDC grade suggests that KRAS mutations may be involved in the formation of PDC.

Histologic prognostic markers in stage IIA colorectal cancer: a comparative study

OBJECTIVE

pTNM stage IIA colorectal cancer (CRC) is not currently submitted to any adjuvant treatment due to its good prognosis. Nevertheless, a percentage of cases unexpectedly recur. The aim of this study was to assess and compare the prognostic value and inter-observer agreement of a novel histological grading system based on the counting of poorly differentiated clusters (PDC) of cancer cells and that of conventional histological grade, lymphatic, venous and perineural invasion (LVI, VI, PNI), tumour budding (TB) and tumor border configuration in stage IIA CRC.

MATERIALS AND METHODS

the afore mentioned histological parameters were assessed in 82 stage IIA CRCs. Inter-observer agreement and correlation with tumour relapse were analyzed by using Fleiss-Cohen's weighted K statistics, Fisher exact test and Chi-squared test. The Mantel-Cox log-rank test was applied to assess the strength of association with disease-free interval (DFI).

RESULTS

inter-observer agreement was very good/good in the assessment of PDC presence and grade, while it was moderate at best in the evaluation of the other parameters. The presence of PDC, high PDC grade, LVI and TB were significantly associated with disease progression (p < 0.0001; p = 0.0012; p = 0.0308; p = 0.0002) and shorter DFI (p = 0.0001; p < 0.0001; p = 0.0129; p = 0.0008). PDC presence (p < 0.0001) and TB (p = 0.012) were independent prognostic factors in multivariate analysis.

CONCLUSIONS

our findings suggest that the assessment of PDC may be useful to stratify patients with stage IIA CRC for recurrence risk, and to identify high risk patients who could benefit from adjuvant chemotherapy.

Prognostic significance of grading based on the counting of poorly differentiated clusters in colorectal mucinous adenocarcinoma

Mucinous adenocarcinoma (MAC) of the colon and rectum is a histological entity with still indefinite prognostic significance. Although it was previously designated as poorly differentiated by convention, the most recent World Health Organization guidelines indicate that the level of maturation of the epithelium determines differentiation in MAC and that microsatellite instability status should be taken into account for its histological grading. Nonetheless, precise criteria for grading are not provided, and the prognostic value of histological grading in MAC still remains unclear. In the present study we aimed to investigate the prognostic value of a grading system based on the counting of poorly differentiated clusters (PDC) of neoplastic cells in 108 colorectal MACs and to compare its reproducibility and significance with those of a grading system based on glandular differentiation. We found that PDC grade was more reproducible and significantly associated with disease progression (P = .0089) as well as with death from colorectal cancer (P = .0035) in our MACs, as compared to the grade based on glandular differentiation, which was not associated with any of the clinicopathologic variables. Moreover, PDC grade emerged as a significant, independent prognostic factor of recurrence-free survival (P = .0198) and cancer-specific survival (P = .0293) in MAC. Interestingly, the prognostic value of PDC grade was unaltered following incorporation of mismatch repair system status in grading. In conclusion, we demonstrated for the first time that PDC grading is feasible, reproducible, and prognostically relevant in MAC, which may support its use in routine practice.