Complementary analysis of microsatellite tumor profile and mismatch repair defects in colorectal carcinomas

Clinical implications of intratumor heterogeneity: challenges and opportunities

In this review, we highlight the role of intratumoral heterogeneity, focusing on the clinical and biological ramifications this phenomenon poses. Intratumoral heterogeneity arises through complex genetic, epigenetic, and protein modifications that drive phenotypic selection in response to environmental pressures. Functionally, heterogeneity provides tumors with significant adaptability. This ranges from mutual beneficial cooperation between cells, which nurture features such as growth and metastasis, to the narrow escape and survival of clonal cell populations that have adapted to thrive under specific conditions such as hypoxia or chemotherapy. These dynamic intercellular interplays are guided by a Darwinian selection landscape between clonal tumor cell populations and the tumor microenvironment. Understanding the involved drivers and functional consequences of such tumor heterogeneity is challenging but also promises to provide novel insight needed to confront the problem of therapeutic resistance in tumors.

Pathological bases for a robust application of cancer molecular classification

Any robust classification system depends on its purpose and must refer to accepted standards, its strength relying on predictive values and a careful consideration of known factors that can affect its reliability. In this context, a molecular classification of human cancer must refer to the current gold standard (histological classification) and try to improve it with key prognosticators for metastatic potential, staging and grading. Although organ-specific examples have been published based on proteomics, transcriptomics and genomics evaluations, the most popular approach uses gene expression analysis as a direct correlate of cellular differentiation, which represents the key feature of the histological classification. RNA is a labile molecule that varies significantly according with the preservation protocol, its transcription reflect the adaptation of the tumor cells to the microenvironment, it can be passed through mechanisms of intercellular transference of genetic information (exosomes), and it is exposed to epigenetic modifications. More robust classifications should be based on stable molecules, at the genetic level represented by DNA to improve reliability, and its analysis must deal with the concept of intratumoral heterogeneity, which is at the origin of tumor progression and is the byproduct of the selection process during the clonal expansion and progression of neoplasms. The simultaneous analysis of multiple DNA targets and next generation sequencing offer the best practical approach for an analytical genomic classification of tumors.

Tumor heterogeneity: mechanisms and bases for a reliable application of molecular marker design

Tumor heterogeneity is a confusing finding in the assessment of neoplasms, potentially resulting in inaccurate diagnostic, prognostic and predictive tests. This tumor heterogeneity is not always a random and unpredictable phenomenon, whose knowledge helps designing better tests. The biologic reasons for this intratumoral heterogeneity would then be important to understand both the natural history of neoplasms and the selection of test samples for reliable analysis. The main factors contributing to intratumoral heterogeneity inducing gene abnormalities or modifying its expression include: the gradient ischemic level within neoplasms, the action of tumor microenvironment (bidirectional interaction between tumor cells and stroma), mechanisms of intercellular transference of genetic information (exosomes), and differential mechanisms of sequence-independent modifications of genetic material and proteins. The intratumoral heterogeneity is at the origin of tumor progression and it is also the byproduct of the selection process during progression. Any analysis of heterogeneity mechanisms must be integrated within the process of segregation of genetic changes in tumor cells during the clonal expansion and progression of neoplasms. The evaluation of these mechanisms must also consider the redundancy and pleiotropism of molecular pathways, for which appropriate surrogate markers would support the presence or not of heterogeneous genetics and the main mechanisms responsible. This knowledge would constitute a solid scientific background for future therapeutic planning.

Analysis of DNA mismatch repair proteins expression and BRAF V600E mutation in a subset of early- and late-onset colorectal carcinoma patients in Mexico

BACKGROUND AND AIMS

A third of colorectal carcinomas (CRC) affect patients <50 years of age. Fifteen percent of CRC cases with microsatellite instability are due to inherited germ-line mutations in DNA mismatch repair genes. The rest have an epigenetic hypermethylation of the MLH1 promoter in whom the BRAF V600E mutation is a common hallmark. Immunohistochemistry helps to classify colorectal cancers with 100% specificity and 92% sensitivity. We undertook this study to determine if age is a risk factor for defective MMR protein expression and BRAF mutations in our population and to compare these results with the histopathological tumor features.

METHODS

Immunohistochemistry for MLH1 and MSH2 and RT-PCR BRAF V600E mutation was performed on tissue specimens from 57 patients <50 years of age. Data on age, gender, tumor location, histology, depth of infiltration, and the presence of metastatic lymph nodes were collected. Forty eight patients >50 years of age were used as a control group. A statistical analysis using ANOVA, χ(2), and Spearman's rho test were performed.

RESULTS

Absent MMR protein expression was more prevalent in patients <50 years of age. No BRAF V600E mutations were detected in either group. Medullary and mucinous types were more prevalent among young patients, whereas intestinal type was more frequent in older patients (p = 0.0008). No differences were found regarding clinicopathological stages between groups.

CONCLUSIONS

We found an association between young age and defective MMR expression. No V600E BRAF mutations were detected in either group.

Heterogeneous topographic profiles of kinetic and cell cycle regulator microsatellites in atypical (dysplastic) melanocytic nevi

Atypical (dysplastic) melanocytic nevi are clinically heterogeneous malignant melanoma precursors, for which no topographic analysis of cell kinetic, cell cycle regulators and microsatellite profile is available. We selected low-grade atypical melanocytic nevi (92), high-grade atypical melanocytic nevi (41), melanocytic nevi (18 junctional, 25 compound) and malignant melanomas (16 radial growth phase and 27 vertical growth phase). TP53, CDKN2A, CDKN1A, and CDKN1B microsatellite patterns were topographically studied after microdissection; Ki-67, TP53, CDKN2A, CDKN1A, and CDKN1B expressions and DNA fragmentation by in situ end labeling for apoptosis were topographically scored. Results were statistically analyzed. A decreasing junctional-dermal marker expression gradient was observed, directly correlating with atypical melanocytic nevus grading. High-grade atypical melanocytic nevi revealed coexistent TP53-CDKN2A-CDKN1B microsatellite abnormalities, and significantly higher junctional Ki67-TP53 expression (inversely correlated with CDKN1A-CDKN1B expression and in situ end labeling). Malignant melanomas showed coexistent microsatellite abnormalities (CDKN2A-CDKN1B), no topographic gradient, and significantly decreased expression. Melanocytic nevi and low-grade atypical melanocytic nevi revealed sporadic junctional CDKN2A microsatellite abnormalities and no significant topographic kinetic differences. High-grade atypical melanocytic nevi accumulate junctional TP53-CDKN1A-CDKN1B microsatellite abnormalities, being progression TP53-independent and better assessed in the dermis. Melanocytic nevi and low-grade atypical melanocytic nevi show low incidence of microsatellite abnormalities, and kinetic features that make progression unlikely.

DNA mismatch repair enzyme immunohistochemistry in colorectal cancer: a comparison of biopsy and resection material

BACKGROUND

Microsatellite instability (MSI) in colorectal cancer (CRC) may be predicted using mismatch repair protein (MMRP) immunohistochemistry (immunostaining), allowing focused genetic investigations and potentially influencing therapeutic interventions. Most laboratories perform immunostaining on surgical resection specimens. Endoscopic biopsy specimens are an alternative tissue source for immunostaining. Given the sensitivity of immunostaining to the degree of tissue fixation, endoscopic biopsy material may produce superior staining, based on faster and more thorough fixation. Moreover, in patients receiving neoadjuvant chemotherapy and/or radiotherapy, endoscopic biopsies may be more useful than surgical resection specimens by allowing assessment of MMR status prior to chemotherapy and/or radiotherapy induced changes in tumours. This study examines whether immunostaining for MMRP expression in CRC is as reliable on endoscopic biopsy material as on surgical resection specimens.

METHODS

Immunostaining for MLH1, PMS2, MSH2 and MHS6 was performed on 112 unselected CRC cases with both endoscopic biopsy and surgical resection material available. A single observer blindly examined intensity and distribution of staining and assessed MMRP expression. Two consultant histopathologists reviewed challenging cases. Endoscopic biopsies and surgical resections were compared using non-parametric statistical analysis.

RESULTS

Immunostaining for all four MMRPs on all 112 cases produced conclusive (i.e., fully interpretable) results in endoscopic biopsies. In surgical resection specimens, 10 stains from nine cases were inconclusive (stains for two MMRPs were inconclusive in one case). In cases where conclusive immunostaining was achieved, there was complete agreement in MMRP status between the endoscopic biopsy and corresponding surgical resection specimens. Overall, MMRP loss was identified in 13% of cases; 11% MLH1, 12% PMS2, 1% MSH2, and 1% MSH6. Immunostaining intensity was significantly higher (p < 0.0005) and the distribution of staining was significantly more uniform (p < 0.0005) on endoscopic biopsy than on surgical resection.

CONCLUSION

Endoscopic biopsy provides equal accuracy and easier interpretation of MMRP expression immunostaining compared to surgical resection specimens.

Pathologic research update of colorectal neuroendocrine tumors

Colorectal neuroendocrine tumors (NETs) originate from neuroendocrine cells in the intestinal tract, and represent a small area within oncology, but one which has provided increasing new data during the past years. Although the World Health Organization has determined clinical and histological features to predict prognosis for such tumors, they may not be valid on an individual basis. We aim to give an overview of the recent findings with regard to pathology, molecular genetics and diagnosis of NETs.

Microsatellite instability and mismatch repair protein defects in ovarian epithelial neoplasms in patients 50 years of age and younger

Ovarian malignancies occurring in the setting of hereditary nonpolyposis colorectal carcinoma syndrome typically present in young women, often as the first or "sentinel" cancer, but the frequency of microsatellite instability (MSI) and mismatch repair (MMR) defects in ovarian surface epithelial malignancies in women <or=50 years of age is neither well known nor well tested. Fifty-two ovarian surface epithelial carcinomas, including 4 with synchronous endometrial carcinomas, were identified in patients 50 years of age or younger and evaluated for evidence of MSI and MMR protein deficiency. Each case was tested for MSI by multiplex polymerase chain reaction amplification of the National Cancer Institute reference panel (BAT25, BAT26, D2S123, D5S346, and D17S250) and deficiency of MMR protein expression by immunohistochemistry (MLH1, MSH2, MSH6, and PMS2). MMR protein expression and MSI (in a subset of cases) were also evaluated in 50 unselected ovarian serous tumors of low malignant potential , a tumor common in younger women. Defects in MMR were detected in 5 of 52 (10%) ovarian carcinomas by at least 1 testing method, including 2 of 4 (50%) ovarian cancers presenting with synchronous endometrial cancer. Three of the 5 (60%) ovarian carcinomas were clear cell carcinomas (17% of all pure clear cell carcinomas) and the remaining 2 were high-grade carcinomas with endometrioid and mixed histology. Loss of MSH2 and MSH6 was detected in all of the affected clear cell carcinomas and a synchronous endometrial cancer with endometrioid histology. Loss of 1 or more MMR proteins was initially noted in 10/50 ovarian serous tumors of low malignant potential on tissue microarray, but further testing on full tissue sections showed intact protein expression and microsatellite stability in all informative cases. This study demonstrates a 10% rate of MMR-deficient ovarian cancer in women <or=50 years of age. MMR-deficient ovarian cancer is frequently associated with loss of expression of MSH2 and MSH6 proteins and clear cell histology. The occurrence of MMR inactivation in a significant proportion of ovarian clear cell carcinomas (17% in this study) suggests that this tumor may warrant targeted testing in women <or=50 years of age.

Differential kinetic features by tumour topography in cutaneous small-cell neuroendocrine (Merkel cell) carcinomas

BACKGROUND/OBJECTIVES

Merkel cell carcinomas (MCC) reveal epithelial and neuroendocrine differentiation, but its topographic cell kinetics remains unknown. This study analyses proliferation, apoptosis, and DNA ploidy by topography, features that can help planning therapeutic protocols. This study topographically analyses proliferation, apoptosis, and DNA ploidy.

METHODS

We selected 27 small-cell MCCs (expressing one epithelial and two neural markers, with consistent ultrastructural findings) to evaluate mitotic figure counting, Ki-67 index, apoptosis index based on the in situ end labelling of fragmented DNA (using Escherichia coli DNA polymerase I, Klenow fragment), DNA ploidy, and BCL2 and TP53 immuno-expression. At least 50 high-power fields were screened per topographic compartment (superficial or papillary dermis, and deep or reticular dermis), recording average and standard deviation for each variable. Variables were statistically compared in each tumour compartment using analysis of variance and Student's t-test (significant if P < 0.05).

RESULTS

MCCs revealed superficial aneuploid DNA content, and no topographic differences for proliferation markers. Apoptosis showed significantly lower values in the deep compartment (average, P = 0.0050, and standard deviation, P = 0.0074), correlating with increased BCL2 and TP53 immuno-expressions.

CONCLUSIONS

High homogeneously distributed proliferation and superficial aneuploid DNA content defines MCCs. Apoptosis follows proliferation in superficial compartments, being less variable and proliferation independent in deep compartments, where it is inversely correlated with BCL2/TP53 expression.

Interaction of microsatellite instability and loss of heterozygosity in adenocarcinoma: multiple markers in adenocarcinoma: an introduction to 'Genetic changes in Slovenian patients with gastric adenocarcinoma evaluated in terms of microsatellite DNA'

Gastric cancer is the second most frequent cause of cancer death worldwide, yet the precise mechanisms underlying the different subtypes of gastric carcinogenesis are poorly understood. Improvements in the diagnosis and prognosis of gastric cancer over classical clinicopathologic findings such as TNM stage, age or macroscopic tumor type, now include novel techniques for superficial endoscopic examination, and new strategies for genetically analyzing biopsied specimens. The development of gastric adenocarcinomas, such as that of many tumor classes, represents the cumulative effects of several different types of mutations, and it is now recognized that both the loss of normal DNA repair, as well as the mutation, loss or inhibition of tumor suppressor genes contribute to the genetic instability leading to cancer. It might be logically anticipated that the combined burden of these two defects would synergize in carcinogenesis, but the extent to which such pathways cooperate in promoting cancer is still not yet well understood. Clearly, an enhanced appreciation of the mechanisms and interactions of these pathways would aid development of diagnosis and treatment options.

Microsatellite abnormalities and somatic down-regulation of mismatch repair characterize nodular-trabecular muscle-invasive urothelial carcinoma of the bladder

AIMS

To correlate histological infiltration patterns with genetic and mismatch repair (MMR) profiles in muscle-invasive bladder urothelial carcinomas (UroC).

METHODS AND RESULTS

Infiltration patterns were assessed in the deep compartment of muscle-invasive UroC (nodular-trabecular, 45 cases; infiltrative, 27 cases). Tumour compartment (superficial and deep to muscularis mucosa) analysis included: microsatellite pattern of TP53, RB1, WT1 and NF1 by polymerase chain reaction/denaturing gradient gel electrophoresis; mitotic, Ki67, in situ end labelling (ISEL) indices and DNA ploidy. MMR was assessed by MLH1 and MSH2 sequencing and immunohistochemistry in UroC with two or more abnormal microsatellite loci. Statistical differences were tested using anova and Fisher's exact tests. Infiltrative UroC showed lower Ki67 index 14.94 +/- 4.28, ISEL index 14.1 +/- 10.0 and shorter median survival (20 months) than nodular-trabecular UroC (Ki67 index 20.65 +/- 4.94, ISEL 20.2 +/- 22.7, 37-month survival, respectively). The genetic profile was significantly different for RB1 (P = 0.0003) and NF1 (P = 0.0023) only, being more frequently abnormal in nodular-trabecular UroC. A significant decrease in MLH1 or MSH2 protein expression with no gene mutations was identified in UroC with microsatellite abnormalities and a nodular-trabecular growth pattern.

CONCLUSIONS

Somatic down-regulation of MMR proteins in nodular-trabecular muscle-invasive UroC results in RB1/NF1 microsatellite abnormalities, correlating with higher cellular turnover and longer survival.