631 Background: In single arm studies, HDC (usually single-cycle) with autograft support appeared to produce an unusually high percentage of LTCR in MBC, an observation which was not confirmed in prospective randomised trials (PRT). We have previously reported the results of the protocol-mandated interim three-year analysis of IBDIS I-a, prematurely terminated (post-Bezwoda)PRT of HDC versus CDC in MBC (ASCO 2003). Despite relatively small numbers (110pts), the primary protocol endpoint-event-free survival (EFS i.e. alive without relapse)-was statistically significantly superior for HDC pts. We now present updated results. Methods: PRT in pts without prior CDC for MBC. CDC (mg/m2): doxorubicin 50/ docetaxel 75 (AT) x 4 followed by cyclophosphamide / methotrexate/5FU; versus HD: 3xAT followed by tandem autograft-supported HDC (#1-Ifosphamide12,000/carboplatin AUC18/etoposide 1200; #2:-cyclophosphamide 6000/thiotepa 800). The median five year F/U will coincide with ASCO 2004, however, as median EFS will still be statistically significantly superior in 5/2004 even if all remaining HDC CR relapse immediately, it was decided to analyze the data now, at 55 months of F/U. Results: All are intention to treat. The study remains statistically significantly positive at a median follow-up of 55 months (range 76–30) The median EFS were: HDC 416 and CDC 312 days (EFS: p=0.017 log-rank, RR 0.62). Progression–free survivals were: HDC 439, CDC 322 days (RR=0.57; p=.006). There were 5 treatment-related deaths on HDC, and 2 on CDC. Six of 56 HDC pts are still alive and relapse free (74, 62, 56, 56, 55, 54 months), versus 1 CDC patient (49 months). Nineteen HDC pts are alive, versus 10 CDC (median survival: 961v 804 days, RR=0.68; p=0.08) Conclusion: These results do not justify routine HDC, but, given the failure of other treatments to produce a meaningful rate of LTCR in this “incurable cancer”, do mandate further study of this approach. IBDIS II will soon be open for accrual. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Aventis