Cytogenetics and the biological basis of sarcomas

Molecular approaches to sarcoma therapy

Soft tissue sarcomas comprise a heterogeneous group of aggressive tumors that have a relatively poor prognosis. Although conventional therapeutic regimens can effectively cytoreduce the overall tumor mass, they fail to consistently achieve a curative outcome. Alternative gene-based approaches that counteract the underlying neoplastic process by eliminating the clonal aberrations that potentiate malignant behavior have been proposed. As compared to the accumulation of gene alterations associated with epithelial carcinomas, sarcomas are frequently characterized by the unique presence of a single chromosomal translocation in each histological subtype. Similar to the Philadelphia chromosome associated with CML, these clonal abnormalities result in the fusion of two independent unrelated genes to generate a unique chimeric protein that displays aberrant activity believed to initiate cellular transformation. Secondary gene mutations may provide an additional growth advantage that further contributes to malignant progression. The recent clinical success of the tyrosine kinase inhibitor, STI571, suggests that therapeutic approaches specifically directed against essential survival factors in sarcoma cells may be effective. This review summarizes published approaches targeting a specific molecular mechanism associated with sarcomagenesis. The strategy and significance of published translational studies in six distinct areas are presented. These include: (1) the disruption of chimeric transcription factor activity; (2) inhibition of growth stimulatory post-translational modifications; (3) restoration of tumor suppressor function; (4) interference with angiogenesis; (5) induction of apoptotic pathways; and (6) introduction of toxic gene products. The potential for improving outcomes in sarcoma patients and the conceptual obstacles to be overcome are discussed.

Chemotherapy in soft tissue sarcomaThe Scandinavian Sarcoma Group experience

The Scandinavian Sarcoma Group (SSG) started its first chemotherapy study in soft tissue sarcoma (STS) in 1981 (SSG I). This study evaluated single agent doxorubicin given adjuvant in a prospective randomized trial in patients with high-grade STS. Neither overall survival nor disease-free survival was improved. Combination chemotherapy was hereafter studied in a phase II study (1991-1994) combining ifosfamide and continuous infusion etoposide with growth factor support (SSG X). The response rate in previously untreated patients was high (42%), but complete remissions were few. Analysis made on patients operated after chemotherapy indicated improved survival in this subgroup. Meta-analyses of adjuvant chemotherapy for localised resectable STS in adults, including the SSG I trial, has indicated improved disease-free survival and a trend towards improved overall survival. Presently, SSG is testing whether such a benefit can be found for adjuvant ifosfamide and doxorubicin treatment given after primary surgery in selected patients with high-grade STS and other well defined unfavourable prognostic factors (SSG XIII).

Cytogenetics and the biologic basis of sarcomas

In this past year, a large number of reports have described cytogenetic and biologic studies of sarcomas. The cytogenetic studies provide further evidence that a growing number of sarcomas seem to be defined by consistent chromosomal abnormalities that can be detected using a variety of molecular genetic tests. However, in addition to these specific abnormalities, many sarcomas have other extremely complex genetic changes. This complexity has made it quite difficult to understand the importance of any single abnormality. Laboratory studies complementing these genetic studies have provided further understanding of sarcoma cellular and molecular biology. Importantly, both types of studies have had significant impact in the clinic in the form of more objective diagnostic tests, potential novel prognostic markers, and even new therapeutic strategies. Together, these papers highlight how genetic studies may offer tremendous insight into sarcoma biology. However, they also highlight some limitations of these approaches as well. Novel experimental approaches may be required to facilitate the continued progress in this field toward the development of better therapeutic strategies.

Immunotherapeutic approaches to sarcoma

In the last decade, the most important factor in the rekindled interest in immune therapy for cancer is the development of new methods to identify tumor antigens that can be recognized by T-cells and other immune effectors. In addition, greater knowledge about tolerance and mechanisms of tumor cell evasion from immune effectors has made the prospect of developing clinically effective immune therapies for cancer seem promising. Research in immune therapies for sarcoma has been limited, mainly because of the previous lack of defined tumor antigens in this disease and the low prevalence of sarcoma in the general population. We will review the fundamental concepts of tumor immunobiology, both cellular and humoral, and highlight the new, powerful methods for identifying novel tumor antigens. Further, we will focus on the unique situation presented by sarcoma as the only solid tumor in which many cytogenetic abnormalities have been characterized which encode for unique, tumor-specific fusion proteins that are ideal targets for immune-based therapy. We will review the specifics of vaccine therapy approach to this disease, with emphasis on strategies to improve the immunogenicity of newly defined tumor antigens in sarcoma.

Chemotherapy in soft tissue sarcoma. The Scandinavian Sarcoma Group experience

The first chemotherapy study of soft tissue sarcoma (STS) by the Scandinavian Sarcoma Group was started in 1981 (SSG I). It evaluated the single agent adjuvant doxorubicin in a randomized setting in patients with high-grade STS. No improvement was noted in the overall survival or disease-free survival rate. More intense chemotherapy was thereafter (1991-1994) evaluated in a phase 2 study, introducing ifosfamide and a continuous infusion of etoposide with growth factor (SSG X). The response rate of previously untreated patients was high (42%), but complete remissions were few. Analysis of patients undergoing surgery after preoperative chemotherapy suggested an increased survival. A recent meta-analysis of adjuvant chemotherapy for localized resectable STS in adults, including the SSG I trial, indicated a better disease-free survival and possibly improved overall survival (Thierny et al. 1997). At present, we are studying whether such a benefit can be shown in patients with high-risk prognostic criteria by giving adjuvant ifosfamide and doxorubicin treatment after primary surgery (SSG XIII). In the latter SSG study, started on July 1, 1998, the adjuvant therapy is evaluated in a phase 2 study in selected patients with high-grade STS and other unfavorable prognostic factors.