Clonal heterogeneity in human esophageal squamous cell carcinomas on DNA analysis

High frequency of TGF-beta-receptor-II mutations in microdissected tissue samples from laryngeal squamous cell carcinomas

In this study we analyze 105 paraformaldehyde-fixed and paraffin-embedded tumor samples from 12 patients with invasive squamous cell carcinoma of the larynx for the presence of gene mutations of the complete TGF-beta-receptor-II (TBR-II) gene. This study was conducted on tissue samples following separation of tumor cell groups from adjacent stroma cell compartments by laser microdissection, resulting in pure tumor cell complexes of approximately 50 to 500 cells. We detected 35 different mutations in 5 of the 12 patients analyzed but none in numerous samples of the normal peritumoral stroma or in normal epithelium. Twelve of the mutations were silent and nonfunctional, whereas the 23 relevant mutations were either bp replacements leading to amino acid exchanges or deletions leading to frame shifts and premature stop codons. Except for the so-called "big polyadenine tract" in exon 3 with several similar mutations, no further mutational hot spot was found. In addition we found a correlation between mutations and a loss of typical TGF-beta effects in tumor cells (high cell proliferation rate) but not in the stroma cells (low proliferative capacity, significant de novo deposition of matrix material). This study is the first to identify a high mutational rate of the TBR-II gene in laryngeal squamous cell carcinoma. We show that that only small tumor-cell groups are affected. The molecular abnormalities are variable, and only one hot spot of mutations can be identified (exon 3, big polyadenine tract). These defects and possibly comparable mutations in other proteins of the TGF-beta-signaling cascade seem to be associated with enhanced cell proliferation rates and alterations of the peritumoral matrix.

Genetic heterogeneity in lung and colorectal carcinoma as revealed by microsatellite analysis in plasma or tumor tissue DNA

BACKGROUND

Determination of tumor clonality has implications for molecular characterization and the optimal treatment of cancer. Allelotyping allows detection of the two alleles, maternal and paternal, and provides additional information regarding clonal genetic defects. The presence of allelic imbalances (AI) in tumors is a general event, but is not necessary at the same allele (alternative AI). The authors' goal was to determine whether the presence of alternative AI (AA) was a marker of heterogeneity and prognosis.

METHODS

To further analyze the heterogeneity of lung tumors, tumor DNA released in the plasma was compared with primary tumor DNA from 24 lung carcinoma patients. The comparison was performed by allelotyping using 12 microsatellites targeting 9 chromosomal regions, taking in each case leukocyte DNA as reference. To extend and confirm these observations, 26 primary colorectal carcinomas with paired synchronous liver metastasis were analyzed using an enlarged panel of 33 microsatellites.

RESULTS

AA were observed in 40% (20 of 50) of all patients, in 25% (6 of 24) of lung carcinoma patients but at a higher level, and in 54% (14 of 26) of colorectal carcinoma patients. They affected different chromosome localizations and each tumor stage. In both types of cancer, patients with AA had a higher AI mean frequency in their primary tumor.

CONCLUSIONS

Detection of AA is an original marker of heterogeneous tumors, demonstrating that independent events occurred on specific genetic sites required for cancer progression.

Intratumor genetic heterogeneity in advanced human colorectal adenocarcinoma

Colorectal carcinogenesis is widely accepted as one of the best-characterized examples of stepwise progression. The existing colorectal carcinogenesis model assumes genetic homogeneity of individual tumors for the main known genetic alterations: K-ras and p53 genes point mutations and loss of heterozygosity (LOH) of chromosome 5q and 18q. The object of the present study was to demonstrate the existence of an intratumor genetic heterogeneity in advanced sporadic colorectal carcinoma for these genetic alterations. Using improved tissue microdissection and DNA extraction, for each tumor, amplifiable DNA was obtained from 15 to 20 areas, of which 1 to 2 concerned lymph node metastases (LNM). This study revealed that 10 of 15 (67%) analyzed tumors were heterogeneous for at least 1 genetic alteration, with between 2 and 6 genotypically different clones detected per tumor. No correlation was observed between the genotype of these subclones and histological differentiation or invasive propensity. Intratumor heterogeneity was more frequently observed for LOH than for point mutations, 67% and 58% for LOH at APC and DCC locus, and 20% for mutation of either the K-ras or p53 gene. In 5 of the 9 (56%) heterogeneous cases with available LNM, the genotype observed in the LNM was different from that of the main clone in the primary tumor, and moreover, 2 of the LNM displayed a genotype undetected in the primary tumor. In conclusion, intratumor genetic heterogeneity was demonstrated in advanced sporadic colorectal carcinoma and was represented as topographically distinct genotypic subclones. Taking into account such a significant genetic heterogeneity of colorectal tumors, the use of genetic markers for prognosis management should be reconsidered.

Histological response of cisplatin predicts patients' survival in oesophageal cancer and p53 protein accumulation in pretreatment biopsy is associated with cisplatin sensitivity

The aim of this study was to evaluate whether cisplatin sensitivity relates to patient's prognosis in oesophageal squamous cell carcinoma and to find a useful chemosensitivity molecular marker. 59 oesophageal squamous cell carcinoma (SCC) patients received cisplatin 30 mg/m2/week treatment of two to five cycles, followed by oesophagectomy. We analysed retrospectively whether the histological effect was related to patient's prognosis. Furthermore, to evaluate the relationship between the effect of preoperative cisplatin treatment and p53 and cyclin D1 expression, we investigated p53 and cyclin D1 expression in pretreatment biopsy samples using an immunohistochemical analysis and compared the results with the histological effect to cisplatin in the resected oesophagus. The cases that showed immunohistochemical p53 staining in the pretreatment biopsy samples were resistant to cisplatin (P = 0.032). However, there was no relationship between cyclin D1 expression and histological effect (P = 0.230). Nevertheless, combined analysis of p53 and cyclin D1 can predict histological effect (P = 0.032). The prognosis of cisplatin-sensitive cases was significantly better than that of cisplatin-resistant cases (P = 0.041). Cox's multivariate analysis revealed that the histological effect was an independent prognostic factor. In contrast, p53 protein accumulation and cyclin D1 were not. Histological response after neoadjuvant cisplatin treatment is a prognostic factor for oesophageal SCC and cisplatin chemotherapy may be selected according to the findings of p53 and cyclin D1 expression.

Analyses of microsatellite instability and the transforming growth factor-beta receptor type II gene mutation in sporadic human gastrointestinal cancer

Microsatellite instability (MSI) and transforming growth factor-beta receptor type II (RII) gene mutation have been reported in many types of tumors and their instance seem to vary among the tumors investigated. To determine the relation between MSI and RII gene mutation in sporadic gastrointestinal cancer development, 21 esophageal, 19 gastric, and 27 colorectal cancers were investigated. The presence of MSI was screened by single strand conformation polymorphism (SSCP) method using six microsatellite markers. RII gene mutations were detected by SSCP method and direct sequencing. MSI was detected in seven of 21 (33.3%) esophageal cancers, three of 19 (15.8%) gastric cancers and seven of 27 (25.9%) colorectal cancers. However, RII gene mutations were observed in only two of seven (28.6%) MSI-positive colorectal cancers. Our data suggest that among sporadic gastrointestinal cancers, colorectal cancers seem to be the most frequent target organ involved in carcinogenesis through RII gene mutation, which thus appears to be related to organ specificity.

p53 tumor suppressor gene as a clonal marker in head and neck squamous cell carcinoma: p53 mutations in primary tumor and matched lymph node metastases

In order to define the diagnostic value of p53 tumor suppressor gene as a clonal marker in head and neck squamous cell carcinoma (HNSCC), we investigated p53 mutations in primary tumors (PT) and matched lymph node metastases (LNM); the underlying question being whether differentiation between metastatic disease of a known PT or (a metastasis of) a synchronous or metachronous second tumor is possible by means of p53 sequencing-based mutation analysis. In 15 PT, the p53 status was analyzed, following RNA isolation, cDNA synthesis and polymerase chain reaction amplification, by direct sequencing full-length mRNA. Mutations thus found were confirmed by DNA sequencing analysis of the corresponding exon in the PT. When RNA isolation was defective, DNA sequencing analysis of exons 1 through 11 was performed. In the matched LNM, DNA analysis of the corresponding exon was performed to prove the presence of the same p53 mutation. In the event of small clones not detectable by direct sequencing, an oligo ligation assay was developed to detect a specific mutation. The presence of germline mutations was excluded by DNA sequencing analysis of the corresponding exon of peripheral blood leucocytes. In 14 PT (94%), a mutation was identified. In one PT, no p53 mutation could be identified either after full-length mRNA sequencing or after sequencing exons 1 through 11. In all cases of PT and matched LNM, the mutations proved to be identical. We conclude that p53 mutations develop in carcinogenesis before metastases occur and are maintained during metastasis. Consequently, p53 may serve as a clonal marker not susceptible to change during tumor metastasis. This merits further exploration of the application of p53 mutation analysis in differentiating between metastatic disease from a known PT versus a metastasis of another second PT.

Analyses of microsatellite instability and the transforming growth factor-beta receptor type II gene mutation in sporadic breast cancer and their correlation with clinicopathological features

To determine the incidence of microsatellite instability (MSI) and its relationship with both clinicopathologic parameters and patient survival, 101 cases of breast cancer were investigated. In addition, transforming growth factor-beta (TGF-beta) receptor type II (RII) gene mutation was also examined to clarify the relation to MSI in breast cancer development. MSI and RII gene mutation were screened by single strand conformation polymorphism (SSCP). The mutations of the RII gene were confirmed by a direct sequence. An association between the MSI status and the clinicopathological features was examined to assess the potential of the MSI status as a prognostic indicator in sporadic breast cancer cases. MSI was detected in 12 of 101 (11.9%) breast cancer cases. The positive MSI breast cancer cases showed relatively more advanced disease than negative MSI cases, and also exhibited relatively poorer prognoses. No RII gene mutations were observed in any of the breast cancer cases. Our data suggest that the MSI status may thus be a useful indicator for the prognosis of sporadic breast cancer cases. However, the breast seems to be an infrequent target organ for cancer development through RII gene mutations. As a result, tumor progression through this pathway appears to be related to organ specificity. For positive MSI breast cancers, other target genes therefore still need to be identified.

Heterogeneity of p53 mutational status in esophageal squamous cell carcinoma

In esophageal squamous cell carcinoma, p53 gene mutations have been analyzed for inter- or intra-patient heterogeneity but only a few studies have investigated intratumoral heterogeneity. We investigated this question within individual esophageal cancers, and also in their lymph-node metastases in 8 cases. Analyzing the p53 gene sequence by direct sequencing of polymerase chain reaction products, we found heterogeneity for p53 mutations in the pre-invasive area in 3 esophageal cancers. In all areas sampled in the invasive portion of each cancer, the p53 mutational status was identical in a given tumor. In heterogeneous tumors, the invasive area showed one of the p53 mutations found in the pre-invasive area. In nodal metastases, the p53 mutation was identical to that in the invasive area of each primary tumor. These data suggest that the timing of p53 alteration is not as early as might have been expected, indicating that, in regard to p53 gene alteration, some esophageal cancers are composed of various subclones in the pre-invasive stage with invasiveness developing in one of them, which becomes predominant through clonal selection.