Microsatellite Instability Positive Tumors Research Articles

Molecular characterization of colorectal cancer patients

ResumenIntroducción. El cáncer colorrectal tiene una alta incidencia en la población mundial. Diversas vías moleculares están involucradas en su desarrollo, entre ellas, la inestabilidad cromosómica, la inestabilidad microsatelital y la epigenética.Objetivo. Hacer la caracterización molecular de 44 individuos con cáncer colorrectal esporádico.Materiales y métodos. El análisis de mutaciones en los genes APC, KRAS, TP53 y BRAF se hizo mediante secuenciación de Sanger; la inestabilidad microsatelital se determinó mediante electroforesis capilar utilizando cinco marcadores de repetición corta en tándem (Short Tandem Repeat) y el estado de metilación del promotor del gen MLH1 se hizo con la técnica MS-PCR (Methylation-Specific PCR).Resultados. La frecuencia de mutación de los genes APC, KRAS y TP53 fue del 18,1, 25 y 4,5 %, respectivamente; las mutaciones detectadas se localizaron con mayor frecuencia en el colon derecho. La frecuencia de inestabilidad microsatelital fue del 27,2 % y el 73,1 % en los tumores con metilación en el gen MHL1, y el 91,6 % de los tumores con inestabilidad microsatelital presentaba metilación en el gen MLH1. En el grupo de tumores con estabilidad microsatelital, las mutaciones en los genes APC, KRAS y TP53 fueron más frecuentes que en el grupo de tumores con inestabilidad microsatelital. La metilación del gen MLH1 fue la alteración más predominante.Conclusiones. En los pacientes con cáncer colorrectal evaluados se demostró la presencia de alteraciones moleculares en las diferentes vías genéticas, las cuales son comunes en su carcinogénesis. Los pacientes presentaron un perfil de mutaciones diferente al de otras poblaciones. Los hallazgos obtenidos en este estudio confirman la heterogeneidad molecular descrita en el desarrollo del cáncer colorrectal.

HER2 in metastatic colorectal cancer: anew to target to remember.

Metastatic colorectal canceris the second most common cause of cancer death. Standard chemotherapy in combination with targeted therapies represent the backbone for the treatment of advanced disease. However, options are limited for patients progressing on these regimens. Genetic testing can offer patients the opportunity to benefit from novel therapies, namely immune checkpoint inhibitors in microsatellite instability-positive tumors. HER2 overexpression has recently emerged as a potentially targetable tumor marker in colorectal cancer (CRC). Despite the absence of approvals for anti-HER2 therapies in CRC, many agents such as trastuzumab and pertuzumab were tested and demonstrated significant antitumor activity, even in heavily pretreated patients. Early trials are also evaluating lapatinib, T-DM1, tucatinib and other anti-HER2 agents in patients with metastatic CRC, with promising results.

Abstract 4158: Dissecting the role of zygosity and lineage in Lynch Syndrome-associated microsatellite Instability

Abstract Lynch syndrome (LS) is an inherited condition leading to an increased risk of developing colorectal cancer and other select malignancies. LS patients have germline alterations in mismatch repair (MMR) genes and their tumors often demonstrate microsatellite instability (MSI). With the advent of immune checkpoint blockade, this is of both prognostic and therapeutic significance. Nevertheless, the factors that dictate the presence of the MSI phenotype in tumors diagnosed in LS patients are poorly understood. We integrated germline pathogenicity with somatic alterations in 17,152 prospectively sequenced advanced cancer patients to determine how zygosity and lineage shape the presence and intensity of the somatic MSI phenotype in LS patients. Overall, we identified 117 LS patients (0.68%) with one of 46 distinct cancer types, 111 of which had sufficient purity for somatic assessment. The tumors of 72% (80/111) of these patients had biallelic inactivation of the germline allele as assessed by integrating high-precision mutant allele fractions with allele-specific DNA copy number analysis or, in select low purity tumors, confirmatory immunohistochemistry. Among patients with biallelic inactivation, 73% (58/80) had MSI positive tumors whereas, only 1/31 (3%) of heterozygous tumors were MSI positive, indicating that biallelic inactivation of the germline allele was obligate to drive the somatic MSI phenotype (p-value=5.4e-12). Lineage appears, however, to condition this dependence of MSI status on biallelic inactivation. Leveraging the prevalence of germline MMR mutations in our cohort, zygosity enrichment, and literature curation of MMR penetrance, we classified cancer types as either conventionally Lynch-associated or not. Notably, despite the presence of biallelic inactivation, MSI was not seen in LS patients whose cancers were not conventionally Lynch-associated such as breast, lung, and thyroid cancers among others. The nature and degree of the MSI phenotype also varied as a function of underlying genotype in these patients. Despite comparable mutational burdens, MSH6 germline carriers that were somatic biallelic had lower MSI scores, lower rates of frameshift indels and higher rates of missense mutations than patients with biallelic mutations in other MMR genes. Collectively, these data suggest that the presence of MSI is dictated by lineage-dependent selection for biallelic inactivation in LS tumors, and emerges to differing degrees driven by the underlying genotype, which together has implications for the immunogenicity of resulting tumors and the biomarker of greatest response to immune checkpoint blockade. By expanding our prospective cohort to >30,000 patients with advanced cancer and integrating clinical response to immunotherapy, we will further explore gene-specific variability in MSI patterns observed in LS patients and its effects on outcome and therapeutic response. Citation Format: Preethi Srinivasan, Chaitanya Bandlamudi, Jinru Shia, Alicia S. Latham, Philip Jonsson, Alexander Penson, Sumit Middha, Jackie Hechtman, Ahmet Zehir, Allison Richards, Shweta Chawan, Yelena Kemel, Diana Mandelker, Liying Zhang, David Hyman, Marc Ladanyi, Mark Robson, Kenneth Offit, David Solit, Barry Taylor, Michael Berger, Zsofia Stadler. Dissecting the role of zygosity and lineage in Lynch Syndrome-associated microsatellite Instability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4158.

FGFR2 Point Mutations in 466 Endometrioid Endometrial Tumors: Relationship with MSI, KRAS, PIK3CA, CTNNB1 Mutations and Clinicopathological Features

Mutations in multiple oncogenes including KRAS, CTNNB1, PIK3CA and FGFR2 have been identified in endometrial cancer. The aim of this study was to provide insight into the clinicopathological features associated with patterns of mutation in these genes, a necessary step in planning targeted therapies for endometrial cancer. 466 endometrioid endometrial tumors were tested for mutations in FGFR2, KRAS, CTNNB1, and PIK3CA. The relationships between mutation status, tumor microsatellite instability (MSI) and clinicopathological features including overall survival (OS) and disease-free survival (DFS) were evaluated using Kaplan-Meier survival analysis and Cox proportional hazard models. Mutations were identified in FGFR2 (48/466); KRAS (87/464); CTNNB1 (88/454) and PIK3CA (104/464). KRAS and FGFR2 mutations were significantly more common, and CTNNB1 mutations less common, in MSI positive tumors. KRAS and FGFR2 occurred in a near mutually exclusive pattern (p = 0.05) and, surprisingly, mutations in KRAS and CTNNB1 also occurred in a near mutually exclusive pattern (p = 0.0002). Multivariate analysis revealed that mutation in KRAS and FGFR2 showed a trend (p = 0.06) towards longer and shorter DFS, respectively. In the 386 patients with early stage disease (stage I and II), FGFR2 mutation was significantly associated with shorter DFS (HR = 3.24; 95% confidence interval, CI, 1.35–7.77; p = 0.008) and OS (HR = 2.00; 95% CI 1.09–3.65; p = 0.025) and KRAS was associated with longer DFS (HR = 0.23; 95% CI 0.05–0.97; p = 0.045). In conclusion, although KRAS and FGFR2 mutations share similar activation of the MAPK pathway, our data suggest very different roles in tumor biology. This has implications for the implementation of anti-FGFR or anti-MEK biologic therapies.

Defective Mismatch Repair, Microsatellite Mutation Bias, and Variability in Clinical Cancer Phenotypes

Microsatellite instability is associated with 10% to 15% of colorectal, endometrial, ovarian, and gastric cancers, and has long been used as a diagnostic tool for hereditary nonpolyposis colorectal carcinoma-related cancers. Tumor-specific length alterations within microsatellites are generally accepted to be a consequence of strand slippage events during DNA replication, which are uncorrected due to a defective postreplication mismatch repair (MMR) system. Mutations arising within microsatellites associated with critical target genes are believed to play a causative role in the evolution of MMR-defective tumors. In this review, we summarize current evidence of mutational biases within microsatellites arising as a consequence of intrinsic DNA sequence effects as well as variation in MMR efficiency. Microsatellite mutational biases are generally not considered during clinical testing; however, we suggest that such biases may be clinically significant as a factor contributing to phenotypic variation among microsatellite instability-positive tumors.

Body mass index: Relationship to clinical, pathologic and features of microsatellite instability in endometrial cancer

There is a well known association between obesity and endometrial cancer. We sought to examine the relationships between body mass index (BMI), as a measure of obesity, and known demographic, clinical, and molecular characteristics of microsatellite instability and MLH1 promoter methylation in a cohort of patients with endometrial cancer. Corpus cancer specimens were prospectively obtained from 473 consecutively enrolled patients between 1992 and 2004. Clinical and pathologic data were extracted from review of the medical record. Microsatellite instability (MSI) was evaluated in all tumors, and methylation of the MLH1 promoter was determined for MSI positive tumors. The median (SD) age and BMI were 64.8 years (11.9) and 33.5 (9.4), respectively. Histology included 376 endometrioid (79%), 69 serous/clear cell or mixed (15%), and 28 sarcomas (6%). Median BMI was 32.4 for endometrioid, 31.0 for serous/clear cell or mixed, and 27.8 for sarcomas (p=0.14). BMI was negatively associated with age at surgery (p<0.01). The remainder of analyses excluded sarcoma histology. BMI was associated with stage of disease; patients with stage I/II disease had significantly higher BMI than those with stage III/IV disease (32.6 vs. 30.6; p=0.02). In relation to molecular features of endometrial cancer, BMI was significantly different between MSI positive tumors compared to MSI negative tumors (30.3 vs. 32.7; p=0.02). MSI was also significantly different between tumor histology, occurring with a higher frequency in Type I than Type II tumors (p<0.01). The majority of endometrial cancer patients are obese. Those with higher BMI are more likely to be younger, present with early stage disease, and have MSI negative tumors.

Negative hMSH2 protein expression in pancreatic carcinoma may predict a better prognosis of patients

The prognostic values of immunohistochemical staining for hMSH2 and hMLH1 in patients with pancreatic carcinomas were investigated. Fifty-five patients with histologically proven pancreatic carcinomas were studied. Immunohistochemical staining for hMSH2 and hMLH1 was performed by avidin-biotin-peroxidase complex method with a catalyzed signal amplification system. Tumor cells that exhibited an absence of nuclear staining in the presence of non-neoplastic cells with nuclear staining were considered to have an abnormal pattern. Four tumors (7.3%) demonstrated abnormal hMS2-negative staining. One tumor (1.8%) had abnormal hMLH1-negative staining and this tumor showed negative hMSH2 staining. No particular clinicopathologic factor such as tumor location, histology, T-factor, N-factor and TNM-stage were observed in patients with negative hMSH2 staining tumors. Median survival time (MST) of patients with hMSH2-negative tumors was comparatively longer than that of patients with hMSH2-positive tumors, however, there was no significant difference between MSTs of the two groups (56 months vs. 14 months; p=0.16). We concluded that negative hMSH2 immunohistochemical staining in the pancreatic carcinomas may demonstrate certain patients, but not all, who had microsatellite instability-positive tumors. The patients with hMSH2-negative tumors may have better prognoses than those with hMSH2-positive tumors. To clarify these findings, further large number of pancreatic carcinomas must be investigated.

Comparison of clinicopathologic characteristics and genetic alterations between microsatellite instability-positive and microsatellite instability-negative sporadic colorectal carcinomas in patients younger than 40 years old.

Many studies have demonstrated that sporadic microsatellite instability-positive colorectal cancers share several clinicopathologic features with hereditary nonpolyposis colorectal cancers, including right-sided location, young age of onset, characteristic histomorphologic features, and a good prognosis. The aim of this study was to define distinct clinicopathologic features of sporadic microsatellite instability-positive colorectal cancers and to compare genotypic characteristics between microsatellite instability-positive and microsatellite instability-negative colorectal cancers in a young group. We analyzed 61 cases of young patients (<40 years old) with colorectal cancers for microsatellite instability at five mononucleotide and three dinucleotide repeats, loss of heterozygosity at APC and DCC, and K-ras and p53 mutations. Microsatellite instability status was correlated with molecular genetic factors and clinicopathologic parameters. Microsatellite instability positivity was detected in 19 (31.1 percent) of 61 cases. Allelic alterations in TGFbetaRII, BAX, and IGFIIR were observed exclusively in microsatellite instability-positive tumors (63.1, 26.3, and 26.3 percent, respectively). Microsatellite instability-positive tumors exhibited a lower frequency of the p53 mutation (10.5 percent) than microsatellite instability-negative tumors (47.6 percent; P < 0.05). However, microsatellite instability status was not associated with APC or DCC allelic deletion or with the K-ras mutation. Microsatellite instability-positive colorectal cancers exhibited a proclivity toward proximal location, expansive growth pattern, and large tumor size (P < 0.05). Microsatellite instability-positive colorectal cancers had lower preoperative serum carcinoembryonic antigen levels (P < 0.05), a less advanced stage at presentation (P < 0.05), and a tendency toward better prognosis (P = 0.051) than microsatellite instability-negative colorectal cancers. However, there was no difference between microsatellite instability-positive and microsatellite instability-negative colorectal cancers regarding gross features, tumor grade, and extracellular mucin production. These results suggest that sporadic microsatellite instability-positive colorectal cancers in young patients have different histomorphologic features from microsatellite instability-negative colorectal cancers and hereditary nonpolyposis colorectal cancers, some overlap of genetic alterations on multistep carcinogenesis with microsatellite instability-negative colorectal cancers, and a tendency for better prognosis.

‘‘Second Hit’’ in Sebaceous Tumors from Muir–Torre Patients with Germline Mutations in MSH2: Allele Loss is Not the Preferred Mode of Inactivation

Muir-Torre syndrome is an autosomal-dominant inherited disorder predisposing to both sebaceous skin tumors and internal neoplasms. In a significant proportion of Muir-Torre syndrome patients skin tumors exhibit microsatellite instability as a hallmark of hereditary nonpolyposis colorectal cancer. Most individuals predisposed to hereditary nonpolyposis colorectal cancer harbor a germline mutation in the DNA mismatch repair genes MSH2 or MLH1. In Muir-Torre syndrome the vast majority of germline mutations have been identified in MSH2. Microsatellite instability in tumor tissue develops after somatic inactivation of the corresponding second mismatch repair allele ("second hit"). So far, the mechanisms of somatic inactivation of the second allele in microsatellite instability positive tumors from patients with known mismatch repair germline mutations are not well understood. We examined whether allele loss (loss of heterozygosity) is a frequent mechanism for inactivation of the second MSH2 allele in a sample of nine microsatellite instability positive skin tumors from eight unrelated Muir-Torre patients with known MSH2 germline mutations. Loss of heterozygosity was determined using microsatellite markers or heteroduplex analysis, respectively. Only one of the nine skin tumors exhibited loss of heterozygosity at the MSH2 locus. Thus, we could show in a sample of sebaceous tumors from patients with genetically proven Muir-Torre syndrome that loss of heterozygosity most probably is not the preferred mode of somatic inactivation of the second MSH2 allele.

Microsatellite instability, MLH-1 promoter hypermethylation, and frameshift mutations at coding mononucleotide repeat microsatellites in ovarian tumors.

Microsatellite instability (MI) is frequent in endometrial carcinomas (ECs), but its occurrence in ovarian tumors is uncertain. Microsatellite instability positive ECs frequently are associated with frameshift mutations in coding mononucleotide tracts in IGFIIR, BAX, hMSH6, and hMSH3. DNA from 52 consecutive patients with ovarian tumors (10 benign, 7 borderline, and 35 malignant) was obtained from neoplastic and normal tissue. After preliminary results, the series was expanded by including 41 additional, previously selected, endometrioid and clear cell carcinomas. Microsatellite instability analysis was assessed by evaluating three (CA)n dinucleotide repeats (D2S123, D5S346, D17S250) and two mononucleotide tracts (BAT 25 and BAT 26). Frameshift mutations at coding mononucleotide repeats (IGFIIR, TGF beta II, BAX, hMSH6, and hMSH3) were investigated by single-strand conformation polymorphism analysis and DNA sequencing. MLH-1 methylation was assessed by methylation specific PCR. Microsatellite instability was identified in only 2 of the 52 (3.8%) tumors of the initial series (1 endometrioid and 1 clear cell carcinoma). After expanding the initial series of 15 endometrioid and clear cell carcinomas with 41 additional endometrioid and clear cell carcinomas, MI was found in 7 of the total series of 56 endometrioid and clear cell carcinomas (12.5%). Frameshift mutations in coding mononucleotide tracts were detected in BAX (6 of 7), IGFIIR (1 of 7), and MSH3 (2 of 7). MLH-1 promoter hypermethylation was identified in three of six MI positive tumors. Microsatellite instability was infrequent in this series of ovarian tumors, and it was limited to endometrioid and clear cell carcinomas. Like EC, many ovarian carcinomas with MI follow the same process of MLH-1 promoter methylation and accumulation of mutations in coding mononucleotide tracts.

Validation and simplification of Bethesda guidelines for identifying apparently sporadic forms of colorectal carcinoma with microsatellite instability

BACKGROUND Colorectal tumors with microsatellite instability (MSI) that do not comply with previously defined clinical criteria may be found in recently diagnosed hereditary nonpolyposis colorectal carcinoma families. Until recently, the indications for MSI testing were not clearly established. The objective of the current study was to validate the recently published Bethesda guidelines for MSI testing in a series of patients with apparently sporadic forms of colorectal carcinoma (CRC). METHODS Sixty-two patients with so-called sporadic CRC were included in the current study. MSI was analyzed at seven poly(CA) repeat sequences and at one poly(A) locus. RESULTS Nine of 62 patients (14.5%) had tumors exhibiting MSI at ≥ 2 loci and 7 patients (11%) had MSI at ≥ 3 loci. Patients with MSI positive tumors were younger (P < 0.05), and their tumors more frequently were right-sided (P < 0.02) and more often exhibited a mucinous component (P < 0.05). The Bethesda guidelines were positive in 18% (11 of 62) of patients. The sensitivity of these guidelines in identifying tumors with MSI at ≥ 3 loci was 43% and the positive predictive value (PPV) was 27% (3 of 11 cases). Other variables were considered as alternative criteria to identify CRCs with MSI: age < 45 years and/or a right-sided tumor with a mucinous component. Using these 2 criteria alone, sensitivity increased to 85% and PPV to 46%. CONCLUSIONS In this study group, the use of three clinical criteria as sole indicators for MSI testing in patients with apparently sporadic forms of CRC were significantly more discriminating compared with the Bethesda guidelines, in addition to being substantially easier. Cancer 1999;85:779–85. © 1999 American Cancer Society.

Validation and simplification of Bethesda guidelines for identifying apparently sporadic forms of colorectal carcinoma with microsatellite instability

Colorectal tumors with microsatellite instability (MSI) that do not comply with previously defined clinical criteria may be found in recently diagnosed hereditary nonpolyposis colorectal carcinoma families. Until recently, the indications for MSI testing were not clearly established. The objective of the current study was to validate the recently published Bethesda guidelines for MSI testing in a series of patients with apparently sporadic forms of colorectal carcinoma (CRC). Sixty-two patients with so-called sporadic CRC were included in the current study. MSI was analyzed at seven poly(CA) repeat sequences and at one poly(A) locus. Nine of 62 patients (14.5%) had tumors exhibiting MSI at > or = 2 loci and 7 patients (11%) had MSI at > or = 3 loci. Patients with MSI positive tumors were younger (P < 0.05), and their tumors more frequently were right-sided (P < 0.02) and more often exhibited a mucinous component (P < 0.05). The Bethesda guidelines were positive in 18% (11 of 62) of patients. The sensitivity of these guidelines in identifying tumors with MSI at > or = 3 loci was 43% and the positive predictive value (PPV) was 27% (3 of 11 cases). Other variables were considered as alternative criteria to identify CRCs with MSI: age < 45 years and/or a right-sided tumor with a mucinous component. Using these 2 criteria alone, sensitivity increased to 85% and PPV to 46%. In this study group, the use of three clinical criteria as sole indicators for MSI testing in patients with apparently sporadic forms of CRC were significantly more discriminating compared with the Bethesda guidelines, in addition to being substantially easier.