Microsatellite instability in sarcomas

Special features of sarcomas developed in patients with Lynch syndrome: a systematic review

Lynch syndrome (LS) is a genetic predisposition leading to colorectal and non-colorectal tumors such as endometrial, upper urinary tract, small intestine, ovarian, gastric, biliary duct cancers and glioblastoma. Though not classically associated with LS, growing literature suggests that sarcomas might develop in patients with LS. This systematic review of literature identified 44 studies (N=95) of LS patients who developed sarcomas. It seems that most sarcomas developed in patients with a germline mutation of MSH2 (57%) exhibit a dMMR (81%) or MSI (77%) phenotype, as in other LS-tumors. Although undifferentiated pleomorphic sarcoma (UPS), leiomyosarcoma, and liposarcoma remain the most represented histologic subtype, a higher proportion of rhabdomyosarcoma (10%, especially pleomorphic rhabdomyosarcoma) is reported. Further studies are required to better characterize this sub-population.

Exploring the landscape of immunotherapy approaches in sarcomas

Sarcomas comprise a heterogenous group of malignancies, of more than 100 different entities, arising from mesenchymal tissue, and accounting for 1% of adult malignancies. Surgery, radiotherapy and systemic therapy constitute the therapeutic armamentarium against sarcomas, with surgical excision and conventional chemotherapy, remaining the mainstay of treatment for local and advanced disease, respectively. The prognosis for patients with metastatic disease is dismal and novel therapeutic approaches are urgently required to improve survival outcomes. Immunotherapy, is a rapidly evolving field in oncology, which has been successfully applied in multiple cancers to date. Immunomodulating antibodies, adoptive cellular therapy, cancer vaccines, and cytokines have been tested in patients with different types of sarcomas through clinical trials, pilot studies, retrospective and prospective studies. The results of these studies regarding the efficacy of different types of immunotherapies in sarcomas are conflicting, and the application of immunotherapy in daily clinical practice remains limited. Additional clinical studies are ongoing in an effort to delineate the role of immunotherapy in patients with specific sarcoma subtypes.

Case Report: Dual Checkpoint Inhibition in Advanced Metastatic Osteosarcoma Results in Remission of All Tumor Manifestations-A Report of a Stunning Success in a 37-Year-Old Patient

Background

Patients with unresectable metastasized osteosarcoma have a poor prognosis. Current treatment options do not offer a chance to cure the disease in this situation. Despite the fact that immunotherapy has expanded its indications continuously over previous years, its use is not yet established in osteosarcoma. There is a lack of randomized controlled studies that could show a significant benefit in this rare tumor entity. So far, efficacy of immunotherapy is only reported in individual cases as well as in mouse models. To predict a response to immunotherapy, testing for programmed death-ligand 1 (PD-L1) expression, microsatellite instability (MSI), and tumor mutational burden (TMB) can be useful, but status is not yet clear for most cancer entities.

Methods

Single case study and review of the literature.

Case Presentation

This report presents the case of a 37-year-old patient with metastatic advanced osteosarcoma, who had no more established options for tumor treatment left. PD-L1 expression in the most recent tumor sample was high (tumor proportion score (TPS) 90%, combined positive score (CPS) 92%) but no MSI could be detected. In an individual therapy attempt, an ongoing and profound remission of all tumor manifestations due to four cycles of immunotherapy with ipilimumab and nivolumab was reached. Despite discontinuation of immunotherapy for 3 months due to therapy-related pneumonitis, remission of all tumor manifestations was ongoing, and no detectable relapse in restaging before onset of Nivolumab-maintenance could be observed.

Conclusion

The present case constitutes the first report of an adult patient with metastasized advanced osteosarcoma who reached a deep remission of disease by immunotherapy with ipilimumab and nivolumab, which continued even though immunotherapy had to be interrupted. To verify whether the high expression of PD-L1, as seen in this patient, is a predictive marker for response to immunotherapy in osteosarcoma, requires further investigation.

NGS-analysis to the rescue: dual checkpoint inhibition in metastatic osteosarcoma - a case report and review of the literature

Background: The prognosis and treatment of metastatic osteosarcoma have not changed in the last decades and the responses to chemotherapy in this setting are disappointing. In the past years, immunotherapy has found its place in the treatment of different tumor types. Its role in the treatment of sarcomas, and in particular osteosarcoma, is less clear. Next-generation sequencing (NGS) can help identify patients who could benefit from immunotherapy.Methods: Single case study and review of the literatureCase summary and intervention: We discuss a case of a 26-year-old man with a metastatic osteosarcoma not responsive to several lines of standard chemotherapy. NGS-analysis of resected tumor tissue revealed amplification of PD-L1 and PD-L2, which is associated in literature with response to anti-PD-1/PD-L1 blockade in other tumor types and in osteosarcoma mouse models. Treatment of our patient with the combination of an anti-PD-1 antibody (Nivolumab) and an anti-CTLA4 antibody (Ipilimumab) showed a stabilization of life-threatening retrocardiac tumoral masses that had previous significantly progressed despite radiotherapy, while one bone lesion in the right os ilium was growing and needed treatment with concomitant radiotherapy.Conclusion: To our knowledge, this is the first case report of a metastasized osteosarcoma patient with no further standard treatment options being treated with dual checkpoint inhibition. A complete stabilization of life-threatening retrocardiac lesions could be achieved and with the addition of radiotherapy to a growing bone lesion, the patient is still doing well. NGS-analysis can help identify druggable targets in patients with rare tumors with limited treatment options.Abbreviations: PD-L1: Programmed death-ligand 1; anti-PD-L1: anti-programmed death-ligand 1; PD-1: programmed cell death protein 1; anti-PD-1: anti-programmed cell death protein 1; anti-CTLA4: anti-cytotoxic T-lymphocyte-associated protein 4; AUC: area under the curve; NGS: next-generation sequencing; Gy: Gray; CT scan: computed tomography scan; RCC: renal cell carcinoma; IHC: immunohistochemistry; TMB: tumor mutational burden; NSCLC: Non-small cell lung cancer.

The potentiality of immunotherapy for sarcomas: a summary of potential predictive biomarkers

Sarcomas are rare and heterogeneous malignant tumors of mesenchymal origin. A total of 25-50% of patients treated with initial curative intent will develop as recurrent and metastatic disease. In the recurrent and metastatic setting, effect of chemotherapy is limited; therefore, more effective therapies are urgently desired. As a brake for activation of T cell, PD-1/PD-L1 plays a crucial role in the progression of tumor by altering status of immune surveillance. Some success has been acquired recently in the use of PD-1/PD-L1 inhibitors for the treatment of several solid tumors, for examples, non-small-cell lung cancer and melanoma. Immunotherapeutic strategies based on PD-1/PD-L1 for sarcomas have also been explored these years. As in other cancers, major challenges are identification of biomarkers to predict response for immunotherapy, optimization of patient's benefit and minimization of side effects. Therefore, we focused on potential biomarkers of immunotherapy for treatment of sarcomas in this review.

Integrated molecular characterization of adult soft tissue sarcoma for therapeutic targets

Background

Several studies have investigated the molecular drivers and therapeutic targets in adult soft tissue sarcomas. However, such studies are limited by the genomic heterogeneity and rarity of sarcomas, particularly in those with complex and unbalanced karyotypes. Additional biomarkers are needed across sarcoma types to improve therapeutic strategies. To investigate the molecular characteristics of complex karyotype sarcomas (CKSs) for therapeutic targets, we performed genomic profiling.

Results

The mutational landscape showed that TP53, ATRX, and PTEN genes were highly mutated. CKS samples were categorized into three groups based on copy number variations that were associated with CDK4 and RB1 signatures. Integrated analysis of genomic and transcriptomic data revealed several pathways related to PDGFR, which could be a strategic target for anti-sarcoma therapy.

Conclusions

This study provides a detailed molecular classification of CKSs and proposes several therapeutic targets. Targeted or combinational therapies for treating CKS should be considered before chemotherapy.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0722-6) contains supplementary material, which is available to authorized users.

Clinical and biochemical function of polymorphic NR0B1 GGAA-microsatellites in Ewing sarcoma: a report from the Children's Oncology Group

BACKGROUND

The genetics involved in Ewing sarcoma susceptibility and prognosis are poorly understood. EWS/FLI and related EWS/ETS chimeras upregulate numerous gene targets via promoter-based GGAA-microsatellite response elements. These microsatellites are highly polymorphic in humans, and preliminary evidence suggests EWS/FLI-mediated gene expression is highly dependent on the number of GGAA motifs within the microsatellite.

OBJECTIVES

Here we sought to examine the polymorphic spectrum of a GGAA-microsatellite within the NR0B1 promoter (a critical EWS/FLI target) in primary Ewing sarcoma tumors, and characterize how this polymorphism influences gene expression and clinical outcomes.

RESULTS

A complex, bimodal pattern of EWS/FLI-mediated gene expression was observed across a wide range of GGAA motifs, with maximal expression observed in constructs containing 20-26 GGAA motifs. Relative to white European and African controls, the NR0B1 GGAA-microsatellite in tumor cells demonstrated a strong bias for haplotypes containing 21-25 GGAA motifs suggesting a relationship between microsatellite function and disease susceptibility. This selection bias was not a product of microsatellite instability in tumor samples, nor was there a correlation between NR0B1 GGAA-microsatellite polymorphisms and survival outcomes.

CONCLUSIONS

These data suggest that GGAA-microsatellite polymorphisms observed in human populations modulate EWS/FLI-mediated gene expression and may influence disease susceptibility in Ewing sarcoma.

Microsatellite instability in sarcoma: fact or fiction?

Microsatellite instability (MSI) is a unique molecular abnormality, indicative of a deficient DNA mismatch repair (MMR) system. Described and characterized in the colorectal cancer literature, the MSI-positive phenotype is predictive of disease susceptibility, pathogenesis, and prognosis. The clinical relevance of MSI in colorectal cancer has inspired similar inquisition within the sarcoma literature, although unfortunately, with very heterogeneous results. Evolving detection techniques, ill-defined sarcoma-specific microsatellite loci and small study numbers have hampered succinct conclusions. The literature does suggest that MSI in sarcoma is observed at a frequency similar to that of sporadic colorectal cancers, although there is little evidence to suggest that MSI-positive tumors share distinct biological attributes. Emerging evidence in Ewing sarcoma has demonstrated an intriguing mechanistic role of microsatellite DNA in the activation of key EWS/FLI-target genes. These findings provide an alternative perspective to the biological implications of microsatellite instability in sarcoma and warrant further investigation using sophisticated detection techniques, sensitive microsatellite loci, and appropriately powered study designs.

Biomaterial-induced sarcomagenesis is not associated with microsatellite instability

Sarcomagenesis, in contrast to carcinogenesis, is poorly understood. Microsatellite instability has been implicated in the development of many cancers, in particular those associated with chronic inflammatory conditions. In an experimental animal model, rats developed not only a peri-implantational chronic inflammatory reaction, but also malignant mesenchymal tumors in response to different biomaterials. Therefore, it was the aim of our study to test if the development of biomaterial-induced sarcomas is characterized by a mutator phenotype. A multiplex-PCR approach was designed to screen biomaterial-induced sarcomas for the presence of microsatellite instability. Seven different microsatellite loci were tested in ten tumors for microsatellite instability using a fluorochrome-labelled multiplex-PCR and subsequent fragment analysis. All tumors provided a microsatellite-stable phenotype at all loci tested. Our data suggest that microsatellite instability is rarely or not at all a feature of malignant transformation of biomaterial-induced soft tissue tumors. Thus, there is no evidence that a mutator phenotype is a hallmark of biomaterial-induced sarcomagenesis.

Mismatch repair protein expression and microsatellite instability: a comparison of clear cell sarcoma of soft parts and metastatic melanoma

Clear cell sarcoma of soft parts is a rare soft tissue malignancy that shows phenotypic overlap with cutaneous melanoma but can be distinguished by the presence of a t(12;22) translocation. Microsatellite instability (MSI), a variation in the lengths of short repeat DNA segments in the genome, has been implicated in melanoma tumorigenesis, but is rare or absent in clear cell sarcoma. Defects in the mismatch repair (MMR) enzyme complex correlate with MSI in some tumor types, allowing the use of immunohistochemistry for the MMR proteins hMLH1 and hMSH2 to predict the presence of MSI. To determine if the association between MMR defects and MSI extends to clear cell sarcoma, we compared a group of nine clear cell sarcomas to 11 metastatic melanomas on the basis of MSI and the expression of MMR proteins. MSI was studied using fluorescence-based multiplexed PCR of five loci. Immunohistochemistry was evaluated on formalin-fixed paraffin-embedded tissue for hMLH1, hMHS2 and hMSH6. MSI was present in only 1/9 (11%) clear cell sarcoma case and in 8/11 (73%) melanoma cases. Immunostaining for hMLH1 and hMSH2 was preserved in all the clear cell sarcomas but loss of immunostaining for one or both proteins was seen in 6/11 melanomas (55%). hMSH6 was detected in 7/9 (78%) clear cell sarcomas and 10/11 (91%) of melanomas. Clear cell sarcoma and metastatic melanoma differed significantly with respect to the presence of MSI (P=0.010) and staining for hMLH1 and/or hMSH2 (P=0.014) but not hMSH6 (P=0.57). Mismatch repair, and consequently genomic instability may contribute to tumorigenesis in melanoma but not clear cell sarcoma. Immunostaining for hMLH1 and hMSH2 and MSI analysis may be helpful in the differential diagnosis of large soft tissue or visceral malignancies with melanocytic differentiation.

Chromosomal aberrations and microsatellite instability of malignant peripheral nerve sheath tumors: a study of 10 tumors from nine patients

Malignant peripheral nerve sheath tumor (MPNST) is an uncommon soft tissue neoplasm with a poor prognosis, occurring sporadically or associated with neurofibromatosis type 1 (NF1); however, the histogenesis of MPNST remains unclear, especially in sporadic tumors. There are two major forms of genomic instability in human cancer: chromosomal instability (CIN) and microsatellite instability (MSI). An inverse relationship has recently been demonstrated between CIN and MSI in colorectal cancers. CIN and MSI are suggested to be individual pathways, which are involved in the pathogenesis and which may lead to specific clinical and pathological characteristics. To elucidate the chromosomal aberration as a consequence of CIN and MSI status of MPNST, we karyotyped 10 MPNSTs from nine patients, and examined the MSI of seven microsatellite markers using high-resolution fluorescence microsatellite analysis; 2 out of 10 cases (20%) had normal karyotypes, and 8 out of 10 cases (80%) revealed structural and numerical chromosomal aberrations. Three of the 10 cases (30%) showed near triploidy. The most frequent aberration was -22 (40%), followed by +2, +14, -13, -17, and -18 (30% each). An MSI-low status was observed in 30% of cases; the remaining cases showed microsatellite stability. These findings suggest that chromosomal aberration as a consequence of CIN has a greater role in the pathogenesis of MPNST than does that due to MSI.

Molecular analysis of primary and recurrent giant cell tumors of bone

The status of microsatellite markers located on chromosomes 1p36, 3p25, 5q23, 9p22, 10q23, 10q24, 17p13, and 19q12 was used to determine loss of heterozygosity (LOH) in primary giant cell tumors (GCT) of bone in 12 patients. The cases included primary, locally recurrent, and metastatic GCT; three tumors were classified as malignant GCT, based on their morphological features. Microdissection was performed on 24 paraffin-embedded tissue samples. An average of three separate topographic sites were microdissected from each tumor. Case selection in each instance was based on the availability of paired samples of tumor in primary GCTs and their corresponding recurrences, and the presence of normal tissue. The number of cases studied is too small for statistical studies, and thus the analysis is descriptive. All cases were informative for >80% of the markers used. Both primary GCTs and local recurrences and lung metastases displayed LOH of three or more markers, and intratumoral heterogeneity was frequent. Fractional allelic losses (FAL) were not different in recurrent and nonrecurrent GCT. FAL was greatest (>30%) in the metastatic group of GCT. Allelic losses of 1p, 9q, and 19q regions were frequent in all groups. LOH of 17p (in proximity to the p53 locus) and 9p occurred exclusively in the pulmonary metastases from GCT. LOH of 9q and 19q was present in primary as well as recurrent GCTs and in one malignant GCT. Involvement of 1p (including MYCL) and 9q regions has not been previously reported in GCT of bone. The pattern of LOH evident in the 17 markers used in the present study suggests that GCT with malignant features may follow an evolutionary pathway similar to the usual primary GCT of bone.

Genetic instability in primary leiomyosarcoma of bone

Primary leiomyosarcoma (LMS) of bone is an exceedingly rare entity on which to date no molecular data have been reported. In a series of 6 tumors (5 grade IIB, 1 grade IIA), we assessed the prevailing genetic stability by microsatellite analysis at 7 loci. The IIB tumors demonstrated a rate of genomic loss as high as 90%, accompanied by an intratumoral heterogeneity in 30% of conspicuous markers. High microsatellite instability in the severe type was not observed, although hMLH1 immunostaining was consistently negative. We assume that intraosseous LMS pertains to "deletor phenotype" tumors. We did observe a locus-specific MSI in our marker linked with hMSH2. Immunostaining and allelotyping indicated a knock-out of pRb in all cases, confirming its major role in sarcomas. Only the stage IIB tumors (4 of 5) pointed to p53 inactivation. In addition, the human telomerase subunit-linked markers exhibited high rates of chromosomal loss. The stage IIA tumor still confined to the bone displayed no genetic instability. Moreover, the proliferation index made a clear distinction between the IIA and IIB tumors (5% vs 30%). We propose to further investigate the usefulness of loss of heterozygosity as a progression marker in this entity.

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.

Possible association between tumor-suppressor gene mutations and hMSH2/hMLH1 inactivation in alveolar soft part sarcoma

Alveolar soft part sarcoma (ASPS) is a rare soft tissue tumor of unknown origin and pathogenesis. We clinicopathologically analyzed 16 cases of ASPS and screened for the genetic alterations of various tumor-suppressor genes and oncogenes, including p53, adenomatous polyposis coli (APC), E-cadherin, and beta-catenin, in 11 cases of ASPS. We also examined the expression of hMSH2/hMLH1 of DNA mismatch repair genes by immunohistochemistry, and promoter hypermethylation of these DNA mismatch repair genes by methylation-specific polymerase chain reaction (MS-PCR) to elucidate any possible association between mutation status of these genes and inactivation of the hMSH2/hMLH1 genes. Furthermore, microsatellite instability (MSI) analysis and loss of heterozygosity (LOH) on chromosome 5q analysis were used for some cases of ASPS where DNA derived from normal tissue was available. The 5-year overall survival rate for all of the patients in this study was 68.6%. The 5-year overall survival rates for patients presenting with localized ASPS and for patients with distant metastases were 83.3% and 47.6%, respectively. The high nuclear grade of tumor cells was a significantly adverse prognostic factor (P = 0.0085). Single-strand conformation polymorphism analysis followed by DNA direct sequencing revealed 4 point mutations of the p53 gene in 3 of 11 cases (27.3%), composed of 3 missense mutations and 1 silent mutation. In addition, 1 case with the E-cadherin missense mutation and 1 case with the APC missense mutations were observed, respectively. None of the cases harbored mutation of exon 3 of the beta-catenin gene. Loss of expression of the hMSH2 and hMLH1 genes was observed in 2 (18.2%) and 3 (27.3%) of 11 cases, respectively. All 3 cases with loss of hMLH1 gene expression harbored mutations of the p53 gene. There was a statistically significant correlation between the genetic alteration positive in these tumor-suppressor genes and loss of hMLH1 gene expression (P = 0.024). Methylation-specific PCR did not reveal hypermethylation of the hMSH2/hMLH1 promoter region in any of the cases examined. Three of 8 (37.5%) ASPS cases showed low MSI, and 2 of these 3 cases showed immunohistochemical lack of expression for either hMSH2 or hMLH1. LOH on 5q was present in 2 of 6 (33.3%) informative cases, and both cases showed LOH on the D5S346 marker, a microsatellite marker near the APC locus. Thus, inactivation of hMSH2/hMLH1 of DNA mismatch repair genes seems to have an important role to play in the mutagenesis of the tumor-suppressor genes in ASPS.

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.

Inclusion of malignant fibrous histiocytoma in the tumour spectrum associated with hereditary non-polyposis colorectal cancer

Sarcomas, including the malignant fibrous histiocytomas (MFHs), are not known to be part of the tumour spectrum of hereditary non-polyposis colorectal cancer (HNPCC) as epidemiologically established. Therefore, occurrence of MFH in an HNPCC family may very well be coincidental. HNPCC is associated with germline mutations in DNA mismatch repair genes, including the MSH2 gene. We analysed an MFH diagnosed in a 45-year-old male HNPCC patient carrying a germline MSH2 mutation for HNPCC-associated molecular characteristics, to investigate a possible relationship between the tumour and that mutation. DNA analysis revealed microsatellite instability and loss of one MSH2 copy, and immunohistochemistry showed absence of nuclear MSH2 protein staining. To investigate whether this is a common finding in MFH, microsatellite instability and nuclear MSH2 protein staining was tested for in 5 and 6 sporadic MFHs, respectively. None showed microsatellite instability and all stained positively for MSH2. Together, these findings show that in rare cases, MFH may be part of the HNPCC tumour spectrum.

Microsatellite instability in sacral chordoma

BACKGROUND AND OBJECTIVES

Microsatellite instability (MIN) is an indirect marker of globally defective DNA mismatch repair in the neoplastic cells of cancer patients. Chordomas are rare, primary skeletal malignancies for which few characteristic molecular genetic markers have been identified. Is MIN demonstratable in chordoma?

METHODS

We evaluated sacral chordomas from 12 patients with sacral chordomas for the presence of MIN at 9 different genetic loci from chromosomes 1p, 5q, 7q, 9p, 11p, 12p, 13q, 17p, and 18q. Cells were scraped from glass slides so that tumor and control DNA could be isolated and then amplified by polymerase chain reaction (PCR). Heterozygosity indices were >/= 0.70.

RESULTS

Six patients (50%) demonstrated MIN for at least 1 locus, and 2 patients demonstrated loss of heterozygosity (LOH) for at least 1 locus. Only 1 individual's chordoma manifested microsatellite instability (MIN) and loss of heterozygosity (LOH). Another patient manifested no MIN but LOH at 9p and 18q. Interestingly, this individual had the most aggressive clinical cancer course, presenting with lymph node metastasis and succumbing to widespread metastatic disease.

CONCLUSIONS

Chordomas can be added to the list of malignancies demonstrating MIN. LOH may prove to portend a worse prognosis than MIN when more tumors are examined.

Clear cell sarcoma or malignant melanoma of soft parts: molecular analysis of microsatellite instability with clinical correlation

Malignant melanoma of soft parts, also termed clear cell sarcoma (CCS), is a rare malignancy of neural crest origin which is different from cutaneous malignant melanoma. Although a translocation involving chromosomes 12 and 22 is characteristic of clear cell sarcoma and not malignant melanoma, there are a paucity of methods to differentiate the two. Therefore, a study of microsatellite instability (MIN) was undertaken to determine if mechanisms of DNA mismatch repair can differentiate these malignancies. MIN has been described in a variety of malignancies including 25% of malignant melanomas. Paraffin-embedded neoplastic and non-neoplastic cells were obtained from 11 individuals (five males; six females; age range from seven to 60 years) with CCS. Isolated DNA was PCR amplified at 17 separate microsatellite loci using radioactive-labeled primers. Tumor tissue was compared to normal tissue for each analysis. No MIN was detected. Loss of heterozygosity was detected in only one patient at a single locus (IFNA). The lack of MIN in clear cell sarcoma further defines the distinction between this tumor and malignant melanoma. Clinically, local recurrence and metastasis were indicators of poor outcome. The size of the tumor was not a significant prognostic indicator. Local recurrence, satellitosis, or nodal metastasis was not proven to be uniformly fatal. Utilization of chemotherapy and/or radiation demonstrated no obvious survival advantage. The histologic parameters of mitotic rate and the presence of necrosis were not prognostic. Limb-preserving surgical procedures were as effective as amputation for local disease control. The actuarial survival rate was calculated to be 48% at five years.