The past, present, and future of cytotoxic chemotherapy and pathway-directed targeted agents for soft tissue sarcoma

The individual rarity of the many subtypes of soft tissue sarcomas has historically mandated an empiric approach to systemic therapy. Doxorubicin, first reported to have activity in sarcomas 40 years ago, remains the generalizable first-line treatment of choice for many subtypes, with no other drug or combination having shown an overall-survival advantage. Other cytotoxic agents, such as paclitaxel for angiosarcoma or gemcitabine with docetaxel for leiomyosarcoma, are commonly used for certain histologic subtypes based on relatively small studies. Trabectedin, particularly active against leiomyosarcoma and myxoid liposarcoma, is approved in many countries worldwide but not yet in the United States or Australia. Newer cytotoxic agents, including ifosfamide derivatives, are in current phase III testing. Although advances is systemic therapy of soft-tissue sarcomas have been hampered by their biologic heterogeneity, this diversity also serves as fertile ground for discovery and validation of targetable molecular drivers. The most notable success in this regard has been the development of small molecule therapies for gastrointestinal stromal tumors. Other targets of recent interest include mouse double minute 2 homolog (MDM2) in dedifferentiated liposarcoma and anaplastic lymphoma kinase (ALK) in inflammatory myofibroblastic tumor. Molecular therapies that have shown activity in diverse sarcoma populations include mammalian target of rapamycin (mTOR) inhibitors and vascular endothelial growth factor (VEGF-R) inhibitors. Among the latter, pazopanib demonstrated a progression-free survival over placebo in prior-treated patients with advanced sarcoma, and is now approved for use in the sarcomas in many countries. Efforts to understand the key molecular aberrations in any particular tumor continue towards a goal of individualized sarcoma therapy.