How effective is dose-intensive/myeloablative therapy against Ewing's sarcoma/primitive neuroectodermal tumor metastatic to bone or bone marrow? The Memorial Sloan-Kettering experience and a literature review.

Attempts to improve outcomes of patients with Ewing's sarcoma/primitive neuroectodermal tumor (ES/PNET) metastatic to bone/bone marrow (BM) have focused on chemotherapy dose intensification strategies. We now present results achieved with that approach, as carried out at Memorial Sloan-Kettering Cancer Center (MSKCC) and as reported in the literature. Twenty-one unselected MSKCC patients with newly diagnosed ES/PNET metastatic to bone/BM received the "P6" protocol which includes cycles of cyclophosphamide (4.2 g/m(2))/doxorubicin (75 mg/m(2))/vincristine and cycles of ifosfamide (9 g/m(2))/etoposide (500 mg/m(2)). Patients in complete/very good partial remission (CR/VGPR) after P6 received myeloablative therapy with either total-body irradiation (TBI) (hyperfractionated 15 Gy)/melphalan (180 mg/m(2)) or thiotepa (900 mg/m(2))/carboplatin (1,500 mg/m(2)). We reviewed the literature. Only one MSKCC patient became a long-term event-free survivor; all but one relapse was in a distant site. Initial responses to P6 were CR/VGPR in 19 patients, but eight of them plus two others developed PD while receiving or shortly after completing P6. Eight patients were treated with TBI/melphalan: four relapsed 2 to 7 months after transplantation; two died early of toxicity; one died of pulmonary failure 17 months after transplantation (no evidence of ES/PNET); and one remains in CR at more than 7 years. The three patients treated with thiotepa/carboplatin relapsed 3 to 4 months after transplantation. All reports on large series of unselected patients with ES/PNET metastatic to bone/BM showed similarly unsatisfactory results. Poor outcome was seen with use of active agents for ES/PNET-cyclophosphamide, ifosfamide, doxorubicin, dactinomycin, vincristine, etoposide - at standard dosages for prolonged periods of time and at higher dosages in intensive regimens for short or prolonged periods of time. No improvements in event-free survival rates occurred with successive cooperative group or large single-institutional studies that used increasingly aggressive chemotherapeutic approaches. Inclusion of ifosfamide with or without etoposide made no difference nor did consolidation of remission with myeloablative chemoradiotherapy. Secondary leukemia emerged as a major risk with dose-intensive regimens. The MSKCC experience and findings reported in the literature suggest that dose-intensive use of the chemotherapy agents with established activity against ES/PNET is reaching its efficacy and toxicity limits. A major impact on prognosis awaits the development of entirely novel therapies.