Microsatellite instability in childhood rhabdomyosarcoma is locus specific and correlates with fractional allelic loss

Microsatellite instability and p53 mutation associated with tumor progression in dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP) is a dermal and subcutaneous tumor categorized as a tumor of intermediate malignancy, and its progression in some cases to fibrosarcoma is well known. However, molecular analysis of tumor progression has been limited. The present study investigated microsatellite instability (MSI) of 7 microsatellite markers through high-resolution microsatellite analysis in addition to a mutational analysis of the p53 gene in 44 tumors in 36 patients. The patients were divided into 2 groups: 9 patients with a fibrosarcomatous component in the primary or recurrent/metastasized tumor, designated as the DFSP+FS group, and the remaining 27 patients, designated as the DFSP group. Cases in which the percentage of markers with an additional peak among the markers successfully analyzed was more than 30% was considered MSI high (MSI-H); cases in which microsatellites were stable at all of the successfully examined markers were considered microsatellite stable (MSS); and the remaining cases were considered MSI low (MSI-L). MSI-H cases were observed more frequently in the DFSP+FS group (4 of 9 cases) than in the DFSP group (1 of 27 cases) (P = 0.028, Fischer's exact test). The MSI status of recurrent or metastatic tumors in both the DFSP+FS and the DFSP groups was the same as that in the corresponding primary neoplasms. Furthermore, there was no difference in MSI status between an ordinary DFSP area and a fibrosarcomatous area in 7 tumors that exhibited both areas. p53 mutational analysis revealed 10 point mutations, composed of 4 missense mutations and 6 silent mutations, in 6 of 36 cases (16.7%). A missense mutation was more frequently observed in the DFSP+FS group (3 of 4) than in the DFSP group (1 of 4). Among 3 cases of a missense mutation in the DFSP+FS group, 2 had a mutation only in a fibrosarcomatous area and 1 had a mutation only in a metastatic tumor progressing to fibrosarcoma. These results suggest that MSI and p53 mutations are involved in tumor progression of DFSP to fibrosarcoma as early and late events, respectively.

Microsatellite instability in a pleomorphic rhabdomyosarcoma in a patient with hereditary non-polyposis colorectal cancer

AIMS

To describe the rare occurrence of a pleomorphic sarcoma with microsatellite instability in a patient with hereditary non-polyposis colorectal cancer (HNPCC).

METHODS AND RESULTS

A soft tissue tumour was removed from the upper leg of a patient who had previously been shown to harbour a germ-line MSH-2 mutation. The tumour was analysed with immunohistochemistry and molecular methods. The morphology and immunohistochemical findings were in keeping with a pleomorphic rhabdomyosarcoma. Microsatellite instability was documented in the tumour with molecular methods and in addition loss of MSH-2 expression in the tumour cells was confirmed by immunohistochemistry.

CONCLUSIONS

Although sarcomas do not form part of the HNPCC diagnostic criteria, they may occur in this mismatch repair syndrome and, moreover, may well be caused by the underlying genetic defect.

The clinical importance and prognostic implications of microsatellite instability in sporadic cancer

AIMS

The genetic abnormality known as microsatellite instability (MSI), first identified in colorectal cancer in 1993, has subsequently been recognised in other malignancies. These cancers are caused by a defect in the nuclear mismatch repair system, allowing mutations to accumulate with every cellular division. Hereditary Non Polyposis Colon Cancers (HNPCC) and associated malignancies demonstrating MSI have a unique histological appearance, improved prognosis and altered response to chemotherapy and radiotherapy. This review examines the incidence of MSI and its clinical significance in commonly occurring solid malignancies.

METHOD

A medline based literature search was performed using the key words 'Microsatellite Instability' and the name of the specific malignancy being investigated. Additional original papers were obtained from citations in those articles identified in the original medline search.

RESULTS

MSI has been detected in many solid malignancies although the definition of instability applied has been variable. It is most commonly found in sporadic malignancies that also occur in the HNPCC syndrome such as colorectal, stomach, endometrial and ovarian cancer. MSI may impart a favorable prognosis in colorectal, gastric, pancreatic and probably oesophageal cancers but a poor prognosis in non small cell lung cancer. In clinical studies colorectal cancers demonstrating MSI respond better to chemotherapy while in vitro studies using MSI positive cell lines show resistance to radiotherapy and chemotherapy.

CONCLUSION

MSI may be a useful genetic marker in prognosis and could be an influential factor in deciding treatment options. However, in many cancers its significance remains unclear and more evaluation is required.

Microsatellite instability and its relevance to cutaneous tumorigenesis

Increasing evidence suggests that human tumors sequentially accumulate multiple mutations that cannot be explained by the low rates of spontaneous mutations in normal cells (2-3 mutations/cell). The mathematical models estimate that for the solid tumors to develop, as many as 6-12 mutations are required in each tumor cell. Therefore, to account for such high mutation rates, it is proposed that tumor cells are genetically unstable, i.e. they have genome-wide mutations at short repetitive DNA sequences called microsatellites. Microsatellite repeats are scattered throughout the human genome, primarily in the non-coding regions, and can give rise to variants with increased or reduced lengths, i.e. microsatellite instability (MSI). This instability has been reported in an increasing number of cutaneous tumors including: melanocytic tumors, basal cell carcinomas and primary cutaneous T-cell lymphomas. Moreover, MSI has been observed in skin tumors arising in the context of some hereditary disorders such as Muir-Torre syndrome, Von Recklinghausen's disease and disseminated superficial porokeratosis. While MSI in some of these disorders reflects underlying DNA replication errors, the mechanism of instability in others is still unknown. Thus far, MSI is considered to be a distinct tumorigenic pathway that reveals surprising versatility. The ramifications for cutaneous neoplasms warrant further investigation.

Microsatellite alterations in various sarcomas in Japanese patients

To determine the usefulness of microsatellite analysis in the differential diagnosis of various sarcomas, we investigated microsatellite alterations at 12 microsatellite loci by polymerase chain reaction and electrophoresis in 39 Japanese patients with sarcomas. The sarcomas were: osteosarcoma, Ewing's sarcoma, chondrosarcoma, liposarcoma, leiomyosarcoma, epithelioid leiomyosarcoma, rhabdomyosarcoma, synovial sarcoma, and malignant fibrous histiocytoma. We also examined ten leiomyomas to contrast with leiomyosarcoma. No microsatellite instability (MSI) or loss of heterozygosity (LOH) were found in Ewing's sarcoma, chondrosarcoma, epithelioid leiomyosarcoma, malignant fibrous histiocytoma, and leiomyoma. Only three patients, one each with liposarcoma, leiomyosarcoma, and synovial sarcoma, manifested MSI, whereas, osteosarcoma, liposarcoma, leiomyosarcoma, rhabdomyosarcoma, and synovial sarcoma manifested LOH, with an incidence of 43%, 14%, 86%, 20%, and 75%, respectively. Interestingly, three patients showed unusual patterns of LOH, probably due to intratumoral heterogeneity. Kaplan-Meier analysis revealed that LOH on 11p was predictive of poor prognosis in osteosarcoma. The low incidence of MSI indicates that MSI is not necessary for neoplastic transformation in sarcomas. However, the very high incidence of LOH in leiomyosarcoma indicates that microsatellite analysis may serve for the differential diagnosis of leiomyosarcoma versus leiomyoma. Microsatellite analysis may also predict prognosis in osteosarcoma.

Optimized PCR labeling in mutational and microsatellite analysis

To optimize the labeling and visualization of PCR products we tested different variables, including deoxynucleotide concentration and ratio, dilution of labeled product, number of PCR cycles, and use of one-step or nested labeling protocols. Labeling was achieved using a fixed amount of labeled dATP, whose relative specific activity was varied by adding increasing amounts of cold dATP. Optimal PCR-labeling intensity was reached at dATP concentrations between 0.9 and 7.0 micromol/L, with a peak at 1.8 micromol/L. This concentration corresponded to an optimal ratio between the increase in specific activity and the decrease in DNA yield. Nucleotide imbalances >1:2 were not advantageous. Mutational analysis by single-strand conformational polymorphism (SSCP) was used to validate PCR-labeling protocols. The limiting nucleotide concentrations did not affect SSCP. Clear SSCP patterns were obtained using DNA templates of different sizes derived from several genes. SSCP patterns obtained using one-step or nested PCR-labeling protocols were equivalent and were visualized after overnight exposure, using [alpha35S]dATP as the label. Dilutions of labeled products ranging between 1:10 and 1:2.5 influenced SSCP patterns, and the lowest dilution tested produced better-defined and more-intense signals. Optimized SSCP conditions allowed the detection of novel and previously characterized nucleotide variants. Clear microsatellite typing was also obtained using optimized protocols and [alpha35S]dATP as the label.