Detection of Occult Metastases in Sentinel Lymph Nodes From Colon Cancer Patients by K-ras Mutation Peptide Nucleic Acid Clamp PCR

Assessment of clinically related outcomes and biomarker analysis for translational integration in colorectal cancer (ACROBATICC): study protocol for a population-based, consecutive cohort of surgically treated colorectal cancers and resected colorectal liver metastasis

Background

More accurate predictive and prognostic biomarkers for patients with colorectal cancer (CRC) primaries or colorectal liver metastasis (CLM) are needed. Outside clinical trials, the translational integration of emerging pathways and novel techniques should facilitate exploration of biomarkers for improved staging and prognosis.

Methods

An observational study exploring predictive and prognostic biomarkers in a population-based, consecutive cohort of surgically treated colorectal cancers and resected colorectal liver metastases. Long-term outcomes will be cancer-specific survival, recurrence-free survival and overall survival at 5 years from diagnosis. Beyond routine clinicopathological and anthropometric characteristics and laboratory and biochemistry results, the project allows for additional blood samples and fresh-frozen tumour and normal tissue for investigation of circulating tumour cells (CTCs) and novel biomarkers (e.g. immune cells, microRNAs etc.). Tumour specimens will be investigated by immunohistochemistry in full slides. Extracted DNA/RNA will be analysed for genomic markers using specific PCR techniques and next-generation sequencing (NGS) panels. Flow cytometry will be used to characterise biomarkers in blood. Collaboration is open and welcomed, with particular interest in mutual opportunities for validation studies.

Status and perspectives

The project is ongoing and recruiting at an expected rate of 120–150 patients per year, since January 2013. A project on circulating tumour cells (CTCs) has commenced, with analysis being prepared. Investigating molecular classes beyond the TNM staging is under way, including characteristics of microsatellite instability (MSI) and elevated microsatellite alterations in selected tetranucleotides (EMAST). Hot spot panels for known mutations in CRC are being investigated using NGS. Immune-cell characteristics are being performed by IHC and flow cytometry in tumour and peripheral blood samples. The project has ethical approval (REK Helse Vest, #2012/742), is financially supported with a Ph.D.-Grant (EMAST project; Folke Hermansen Cancer Fund) and a CTC-project (Norwegian Research Council; O. Nordgård). The ACROBATICC clinical and molecular biobank repository will serve as a long-term source for novel exploratory analysis and invite collaborators for mutual validation of promising biomarker results. The project aims to generate results that can help better discern prognostic groups in stage II/III cancers; explore prognostic and predictive biomarkers, and help detail the biology of colorectal liver metastasis for better patient selection and tailored treatment. The project is registered at http://www.ClinicalTrials.gov NCT01762813.

Clinical relevance of circulating KRAS mutated DNA in plasma from patients with advanced pancreatic cancer

We used KRAS mutations to investigate the clinical relevance of circulating tumor DNA (ctDNA) measurements in patients with advanced pancreatic cancer. Fifty-three blood samples were collected from 14 prospectively recruited patients prior to chemotherapy (gemcitabine or FOLFIRINOX) and subsequently every month during treatment. Samples were processed by density centrifugation and plasma DNA isolation. A Peptide-nucleic acid-clamp PCR was then used to detect KRAS mutations (present in >90% of pancreatic cancers) as a surrogate marker for ctDNA. Plasma samples from 29 healthy individuals were analyzed as a reference group. Results were compared to conventional monitoring measures and survival data. Median follow-up time was 3.7 months (range 0.6-12.9 months). Ten (71%) patients had a positive KRAS status in the plasma samples obtained prior to chemotherapy, indicating the presence of ctDNA. Among the patients who were ctDNA-positive before chemotherapy, nine (90%) experienced disease progression during follow-up, compared to one (25%) of four ctDNA-negative patients (P = 0.01). The pre-therapy ctDNA level was a statistically significant predictor of both progression-free and overall survival (P = 0.014 and 0.010, respectively). Of the 14 patients, ten had ≥2 follow-up samples; in several of these patients, the ctDNA level changed substantially during the course of chemotherapy. Changes in ctDNA levels corresponded both with radiological follow-up data and CA19-9 levels for several patients. This pilot study supports the hypothesis that ctDNA may be used as a marker for monitoring treatment efficacy and disease progression in pancreatic cancer patients. Recruitment of more patients is ongoing to corroborate these findings.

[The intraoperative study of the sentinel lymph node was made possible through molecular analysis: a new concept and new applications for colon cancer?]

Sentinel lymph node (SLN) is a concept but also a technical possibility that can be studied and applied to almost all organs with cancer. For colorectal cancer surgery, some possibilities of using the SLN are possible, other implausible and some completely new especially aware of possible analysis of SLN by a molecular biology technique. The orientation of dissection or "lymph road mapping" can be designed for this case or the surgeon may want to limit his actions, particularly in patients with a history of colonic surgical resection, to keep the digestive function in maintaining vascular axes considered not involved in the metastatic process. The use of the single analysis of SLN to determine the positive or negative status of the cleaning has failed because of the frequency of false negatives in part to the size of colic advanced cancers at diagnosis. The use of "ultra-stading" by multiple section or exhaustion of the block, can lead to reconsider a stage N0 to N1 as a point, if the analysis technique remains in HES. Unlike the "ultra-stading" by RT- PCR or immunohistochemistry was even more discussed and seems not equivalent in terms of prognosis and therefore no giving formally justification for adjuvant therapy. Currently, a new technique for molecular biology, named "OSNA", allows an analysis of all the SLN in less than 45 minutes. It is therefore possible to obtain during surgery analysis of a node with the same level of information than traditional analysis using HES. If this node is positive and if the strategy in case of positive lymph nodes was determined prior for this patient, it is possible to anticipate this strategy and place after colectomy during the same anesthesia, venous access quickly to start postoperative chemotherapy. This new technique for analyzing lymph applied to the SLN opens a new potential application of this concept in digestive oncology.

Influence of microsatellite instability and KRAS and BRAF mutations on lymph node harvest in stage I-III colon cancers

Lymph node (LN) harvest is influenced by several factors, including tumor genetics. Microsatellite instability (MSI) is associated with improved node harvest, but the association to other genetic factors is largely unknown. Research methods included a prospective series of stage I-III colon cancer patients undergoing ex vivo sentinel-node sampling. The presence of MSI, KRAS mutations in codons 12 and 13, and BRAF V600E mutations was analyzed. Uni- and multivariate regression models for node sampling were adjusted for clinical, pathological and molecular features. Of 204 patients, 67% had an adequate harvest (≥ 12 nodes). Adequate harvest was highest in patients whose tumors exhibited MSI (79%; odds ratio [OR] 2.5, 95% confidence interval [CI] 1.2-4.9; P = 0.007) or were located in the proximal colon (73%; 2.8, 1.5-5.3; P = 0.002). In multiple linear regression, MSI was a significant predictor of the total LN count (P = 0.02). Total node count was highest for cancers with MSI and no KRAS/BRAF mutations. The independent association between MSI and a high LN count persisted for stage I and II cancers (P = 0.04). Tumor location in the proximal colon was the only significant predictor of an adequate LN harvest (adjusted OR 2.4, 95% CI 1.2-4.9; P = 0.01). An increase in the total number of nodes harvested was not associated with an increase in nodal metastasis. In conclusion, number of nodes harvested is highest for cancers of the proximal colon and with MSI. The nodal harvest associated with MSI is influenced by BRAF and KRAS genotypes, even for cancers of proximal location. Mechanisms behind the molecular diversity and node yield should be further explored.

Prognostic relevance of occult metastases detected by cytokeratin 20 and mucin 2 mRNA levels in sentinel lymph nodes from colon cancer patients

PURPOSE

To investigate the prognostic value of occult metastases detected by quantitative measurements of candidate biomarkers in sentinel lymph nodes (SLNs) from patients curatively resected for colon cancer.

METHODS

Resection specimens from consecutive patients undergoing surgery for localized colon cancer were subjected to ex vivo SLN mapping. SLNs were examined for the presence of metastases by routine hematoxylin-erythrosin-safranin staining and by cytokeratin 20 (CK20) and mucin 2 (MUC2) mRNA quantification. The patients were stratified according to KRAS and BRAF mutation status and microsatellite instability status in their primary tumors. Survival end points were analyzed by Kaplan-Meier survival estimates and log-rank tests.

RESULTS

A total of 817 SLNs were identified in 206 (97 %) of the 213 included patients. Routine histological examination of SLNs and other regional lymph nodes identified 63 patients with positive nodes (pN+), of which 42 (67 %) were positive in one or more SLNs (sensitivity 67 %, false-negative rate 33 %). On the basis of the CK20 and MUC2 mRNA levels in SLNs, occult metastases were suggested in 86 (60 %) and 52 (36 %) of the 143 otherwise LN-negative (pN0) patients, respectively. Survival analysis with a median 3.6-year follow-up revealed that MUC2 mRNA quantification had significant prognostic value in SLNs from all patients; however, occult SLN metastasis detection did not.

CONCLUSIONS

Occult SLN metastases detected by CK20 and MUC2 mRNA quantification had limited prognostic value.

Metachronous metastasis- and survival-analysis show prognostic importance of lymphadenectomy for colon carcinomas

Background

Lymphadenectomy is performed to assess patient prognosis and to prevent metastasizing. Recently, it was questioned whether lymph node metastases were capable of metastasizing and therefore, if lymphadenectomy was still adequate. We evaluated whether the nodal status impacts on the occurrence of distant metastases by analyzing a highly selected cohort of colon cancer patients.

Methods

1,395 patients underwent surgery exclusively for colon cancer at the University of Lübeck between 01/1993 and 12/2008. The following exclusion criteria were applied: synchronous metastasis, R1-resection, prior/synchronous second carcinoma, age < 50 years, positive family history, inflammatory bowel disease, FAP, HNPCC, and follow-up < 5 years. The remaining 421 patients were divided into groups with (TM+, n = 75) or without (TM-, n = 346) the occurrence of metastasis throughout a 5-year follow-up.

Results

Five-year survival rates for TM + and TM- were 21% and 73%, respectively (p < 0.0001). Survival rates differed significantly for N0 vs. N2, grading 2 vs. 3, UICC-I vs. -II and UICC-I vs. -III (p < 0.05). Regression analysis revealed higher age upon diagnosis, increasing N- and increasing T-category to significantly impact on recurrence free survival while increasing N-and T-category were significant parameters for the risk to develop metastases within 5-years after surgery (HR 1.97 and 1.78; p < 0.0001).

Conclusions

Besides a higher T-category, a positive N-stage independently implies a higher probability to develop distant metastases and correlates with poor survival. Our data thus show a prognostic relevance of lymphadenectomy which should therefore be retained until conclusive studies suggest the unimportance of lmyphadenectomy.

Heterogeneous distribution of K-ras mutations in primary colon carcinomas: implications for EGFR-directed therapy

PURPOSE

K-ras mutations predict resistance against epidermal growth factor receptor (EGFR)-directed therapy of metastatic colorectal cancer (CRC). The purpose of this study was to analyze the distribution of K-ras mutations in primary tumors and corresponding sentinel lymph nodes (SLNs) from colon cancer patients.

METHODS

Tumor biopsies and SLNs from 158 patients with non-metastatic colon cancer were analyzed for K-ras mutations in codons 12 and 13 by a sensitive and quantitative peptide nucleic acid clamp PCR assay.

RESULTS

Analyses of single fresh-frozen tumor biopsies revealed K-ras mutations in 67 (42%) of the patients. Apparently low levels of K-ras mutations in 13 of the mutated primary tumors and the presence of K-ras mutations in SLNs from seven patients with a wild-type primary tumor biopsy suggested possible intratumoral heterogeneity for 20 of the patients. To confirm this hypothesis, we analyzed tissue sections from all available formalin-fixed, paraffin-embedded (FFPE) tumor blocks from these 20 patients. Ten of the patients had a mixture of tissue sections positive and tissue sections negative for K-ras mutations, two patients had K-ras mutations in all sections, and eight patients had no detectable K-ras mutations in tumor FFPE tissue blocks. Among these eight patients, five had K-ras mutations detected in SLNs. Thus, evidence supporting a heterogeneous distribution of K-ras mutations was obtained for 15 patients.

CONCLUSIONS

Heterogeneous distribution of K-ras codon 12 and 13 mutations within primary tumor, or between primary tumor and lymph node metastases, was demonstrated for 15 (20%) of 74 colon cancer patients having K-ras mutations. This may have implications for tissue sampling routines with regard to EGFR-directed therapy of CRC, both in adjuvant and metastatic settings.

Heterogeneity of KRAS status may explain the subset of discordant KRAS status between primary and metastatic colorectal cancer

BACKGROUND

KRAS status is a useful predictive marker for anti-epidermal growth factor receptor antibody therapy.

OBJECTIVE

This study aimed to examine the concordance rate of KRAS mutation status between corresponding primary and metastatic colorectal cancer lesions, and also among multiple metastatic tumors. Furthermore, we examined the heterogeneity of KRAS mutations with respect to discordant KRAS status between primary and metastatic tumors.

DESIGN AND SETTINGS

This study was retrospective in design.

PATIENTS

Forty-three patients with primary tumors and 113 metastatic tumors were studied.

MAIN OUTCOME MEASURES

The KRAS mutational status was determined by the peptide nucleic acid clamp real-time polymerase chain reaction TaqMan assay. We also performed sequencing analysis to validate the KRAS mutational status. When KRAS status differed between primary and metastatic tumors, we examined the heterogeneity of KRAS status within individual primary tumors by microdissecting multiple samples in each patient.

RESULTS

The frequency of KRAS mutations in primary tumors was 34.9%. A high concordance rate of KRAS (88.4-91.7%) mutations was observed between primary and metastatic tumors. All 5 cases (11.6%) with discordant KRAS status had heterogeneous KRAS status in primary tumors. However, in 10 concordant cases all microdissected areas showed an identical KRAS mutational status within each patient. The KRAS mutational statuses in all multiple liver and/or lung metastatic tumors were the same as those of the primary tumor.

LIMITATIONS

We could not validate KRAS status in microdissected samples by the direct sequence method that was used in the present study, because the quantity of DNA was not sufficient to perform direct sequencing.

CONCLUSION

KRAS status in a primary site may be used for selecting patients who would benefit from anti-epidermal growth factor receptor therapy. However, KRAS status can be heterogeneous within a primary tumor, and thus different parts of such tumors should be examined for KRAS status to correctly predict the KRAS status in metastatic lesions.