Clinical and Biological Significance of CDK4 Amplification in Well-Differentiated and Dedifferentiated Liposarcomas

Therapeutic pipeline for soft-tissue sarcoma

INTRODUCTION

Soft-tissue sarcomas (STS) represent a heterogeneous group of malignant tumors originating from connective tissues. Over recent years, this heterogeneity has led to a molecular breakdown of STS and subsequent use of targeted agents in several molecularly defined subgroups. After the initial success of imatinib in gastrointestinal stromal tumors, several other compounds have shown promising activity in some but not all subgroups of sarcoma.

AREAS COVERED

This review discusses the rational and clinical results, when available, that support this subtype-directed approach. In the vast majority of cases, these agents have been tested only in patients with advanced disease; as chemotherapeutic agents are developed as non-histotype-specific therapies, they are not discussed here. The PubMed literature was searched using the terms 'sarcoma', 'angiogenesis', 'mTOR' and 'targeted agents'. Proceedings of the annual meeting of the American Society of Clinical Oncology as well as those of the Connective Tissue Oncology Society were also searched for relevant information.

EXPERT OPINION

Many agents are currently developed in a subtype-specific manner in STS and this represents a significant leap forward. However, much remains to be done to improve our understanding of the molecular biology of this heterogeneous group of diseases.

The CDKN2A/CDKN2B/CDK4/CCND1 pathway is pivotal in well-differentiated and dedifferentiated liposarcoma oncogenesis: an analysis of 104 tumors

The MDM2 and CDK4 genes are the main targets of chromosome 12 amplification in well-differentiated and dedifferentiated liposarcomas. Nevertheless, around 10% of these tumors do not amplify CDK4. To find substitutive alterations of CDK4 amplification, we analyzed a large series of liposarcomas by array-CGH, real-time genomic PCR, gene expression array, and real-time RT-PCR. We demonstrate that an alteration in the CDKN2A/CDKN2B/CDK4/CCND1 pathway is present in almost all cases without CDK4 amplification, thereby confirming the pivotal role of this pathway in liposarcoma oncogenesis. Moreover, we show that cell cycle and differentiation are driven by a subtle and complex balance between members of this pathway. Finally, we demonstrate that in tumors without amplification/overexpression of CDK4, the chromosome 1q21-1q23 region is a preferential partner of chromosome 12 amplicon, suggesting that the mechanism of amplification is slightly different in this group of tumors.

Optimising the management of soft tissue tumours

The Royal College of Pathologists of Australasia is developing a series of protocols as an educational tool to assist pathologists in the reporting of relevant information for specific cancer specimens. The protocol for the management of soft tissue tumour resections has recently been released, and this document elaborates the relevant literature on which that protocol drew. Sarcoma is uncommon but is associated with significant morbidity and mortality, and its management is complex. Diagnostic errors are not uncommon and these can have disastrous effects on patient outcome. Sophisticated ancillary testing is often an important adjunct to diagnosis and prognostication. Referral to a specialist sarcoma unit is indicated for both adult and paediatric sarcoma.

An experimental model for the study of well-differentiated and dedifferentiated liposarcoma; deregulation of targetable tyrosine kinase receptors

Therapeutic progress in well-differentiated/dedifferentiated liposarcoma (WDLPS/DDLPS) is hampered by lack of relevant experimental models, thereby limiting comprehensive molecularly based investigations. Our goal is to bridge this experimental gap by establishing and characterizing an in vitro/in vivo model useful for examining WDLPS/DDLPS molecular pathogenesis and also therapeutic screening and testing. WDLPS/DDLPS cells were isolated from freshly resected human surgical specimens and were phenotypically and molecularly characterized. MDM2 amplification was determined via FISH analysis. Adipogenic differentiation was evaluated using Oil Red O staining and western blotting (WB). Tyrosine kinase receptors' (TKRs) expression in pre-adipocytes, adipocytes, WDLPS, and DDLPS cells was determined via western blot analysis. SCID mouse xenograft growth was assessed after subcutaneous and/or intraperitoneal tumor cell injection. There was enhanced proliferation, migration, invasion, survival, and pro-angiogenic capacity in DDLPS cells vs WDLPS cells. DDLPS cells formed tumors in SCID mice whereas WDLPS did not. WDLPS/DDLPS cells, especially those that exhibited baseline PPARγ expression, partially retained terminal adipogenic differentiation capacity. MDM2 amplification was found in all WDLPS/DDLPS cell strains, CDK4 overexpression was observed in LPS cells as compared with normal adipocytes, and enhanced JUN expression and phosphorylation was seen in DDLPS cells as compared with WDLPS cells. The TKRs: MET, AXL, KIT, and IGF-1R were overexpressed in LPS cells vs normal adipocytes and pre-adipocytes. In conclusion, these newly established cellular and xenograft models can facilitate investigation of liposarcomagenesis, dedifferentiation, and tumor progression. Further studies of the molecular deregulations so identified may lead to improved therapeutic strategies for patients afflicted by these unfavorable malignancies.

Array-based comparative genomic hybridization identifies CDK4 and FOXM1 alterations as independent predictors of survival in malignant peripheral nerve sheath tumor

PURPOSE

Malignant peripheral nerve sheath tumors (MPNST) are highly aggressive sarcomas with variable patient survival and few known prognostically relevant genomic biomarkers. To identify survival-associated genomic biomarkers, we performed high-resolution array-based comparative genomic hybridization (aCGH) on a large set of MPNSTs.

EXPERIMENTAL DESIGN

Candidate gene alterations identified by aCGH in 38 MPNSTs were validated at the DNA, RNA, and protein levels on these same tumors and an independent set of 87 MPNST specimens.

RESULTS

aCGH revealed highly complex copy number alterations, including both previously reported and completely novel loci. Four regions of copy number gain were associated with poor patient survival. Candidate genes in these regions include SOX5 (12p12.1), NOL1 and MLF2 (12p13.31), FOXM1 and FKBP1 (12p13.33), and CDK4 and TSPAN31 (12q14.1). Alterations of these candidate genes and several others of interest (ERBB2, MYC and TP53) were confirmed by at least 1 complementary methodology, including DNA and mRNA quantitative real-time PCR, mRNA expression profiling, and tissue microarray-based fluorescence in situ hybridization and immunohistochemistry. Multivariate analysis showed that CDK4 gain/amplification and increased FOXM1 protein expression were the most significant independent predictors for poor survival in MPNST patients (P < 0.05).

CONCLUSIONS

Our study provides new and independently confirmed candidate genes that could serve as genomic biomarkers for overall survival in MPNST patients.

Liposarcoma: molecular genetics and therapeutics

Sarcomas are a group of heterogeneous tumours with varying genetic basis. Cytogenetic abnormalities range from distinct genomic rearrangements such as pathognomonic translocation events and common chromosomal amplification or loss, to more complex rearrangements involving multiple chromosomes. The different subtypes of liposarcoma are spread across this spectrum and constitute an interesting tumour type for molecular review. This paper will outline molecular pathogenesis of the three main subtypes of liposarcoma: well-differentiated/dedifferentiated, myxoid/round cell, and pleomorphic liposarcoma. Both the molecular basis and future avenues for therapeutic intervention will be discussed.

[Lipoma and atypical lipomatous tumor within the same neoplasia: Evidence for a continuous transition]

The case of a lipomatous tumor with a predominant lipoma component and transition to an atypical lipomatous tumor is presented. A deep-seated soft tissue tumor of the right thigh with a maximum size of 14 cm was resected in a 70-year-old female patient. Corresponding to a comparable macroscopic aspect, the lesion revealed the histological features of an ordinary lipoma without atypia in about 80% of the specimen. In the remaining portion (approximately 20%) histopathology showed an atypical lipomatous tumor (ALT, lipoma-like subtype). Immunohistochemistry for MDM 2 and CDK4 revealed no immunoreactivity in the lipoma component, but within the ALT component. Interphase dual-color fluorescence in situ hybridization showed no amplification of the MDM 2 gene and rarely CDK4 gene amplification within the lipoma component, but high level amplification of MDM 2/CDK4 gene in the ALT area, further supporting the morphologically based diagnosis of a lipomatous tumor including areas of a true lipoma and ALT. This case underlines the concept of a continuous stepwise development of lipomatous soft tissue tumors from benign to malignant counterparts as a biological continuum.

The clinical relevance of molecular genetics in soft tissue sarcomas

Bone and soft tissue sarcomas are an infrequent and heterogeneous group of mesenchymal tumors including more than a hundred different entities attending to histologic patterns. Research into the molecular aspects of sarcomas has increased greatly in the last few years. This enormous amount of knowledge has allowed, for instance, to refine the classification of sarcomas, improve the diagnosis, and increase the number of therapeutical targets available, most of them under preclinical evaluation. However, other important key issues, such as sarcomagenesis and the cell of origin of sarcomas, remain unresolved. From a molecular point of view, these neoplasias are grouped into 2 main types: (a) sarcomas showing relatively simple karyotypes and translocations, which originate gene fusions (eg, EWS-FLI1 in Ewing sarcoma) or point mutations (eg, c-kit in the gastrointestinal tumors) and (b) sarcomas showing unspecific gene alterations, very complex karyotypes, and no translocations. The discovery of the early mechanisms involved in the genesis of sarcomas, the more relevant signaling pathways, and the development of genetically engineered mouse models could also provide a new individualized therapeutic strategy against these tumors. This review describes the clinical application of some of the molecular alterations found in sarcomas, some advances in the field of sarcomagenesis, and the development of animal models.

[Atypical lipomatous tumors of the stomach. Clinical, morphological and molecular findings]

Two cases of primary gastric atypical lipomatous tumors (ALT) are presented. In case No.1, a 7x4x3 cm submucosal ALT (lipoma-like subtype) of the antrum/pyloric region in a 60-year-old woman was completely resected. Using interphase dual-color-FISH, MDM2- and CDK4 amplifications could be detected in distinguished amplicons. The patient was continuously free of disease after 56 months. In case No. 2, a 3.5 cm (in diameter) submucosal ALT (lipoma-like subtype) of the gastric body in a 56-year-old woman was completely resected. FISH revealed MDM2 amplification while the CDK4 gene remained in diploid copies. This patient was continuously free of disease after 36 months. The morphologic and molecular biological findings of this rare primary gastric mesenchymal tumor are discussed in comparison with the corresponding soft tissue lesions.