Background: The purpose of this study was to characterize long-term progression-free survivors (LTPFS) of metastatic breast cancer (MBC) following high-dose chemotherapy (HDCT) with autologous stem cell transplantation (ASCT) and to assess the influence of chemotherapy dose in order to identify patients who derive major benefit from this approach.
Patients and methods: We compared patient and tumor characteristics of 16 LTPFS with the characteristics of 118 MBC patients who received HDCT with ASCT at our institution between 1992 and 2000. To estimate the cumulative dose of chemotherapy received, the summation dose intensity product (SDIP) of the different chemotherapy regimens was calculated as recently described by Hryniuk et al. The SDIP of the induction regimens was added to that of the HDCT regimens to yield the total SDIP of the chemotherapy received. Multivariate analysis was performed to describe the influence of the total SDIP and other prognostic factors on progression-free survival (PFS).
Results: LTPFS were mostly < or = 50 years of age and had limited, chemotherapy-sensitive, hormone-responsive MBC. Due to an apparent dose-survival relationship, an increase by 10 units (U) in the SDIP increased the PFS time by 3 months. Independent predictors of an improved PFS were positive estrogen receptors (P = 0.001), positive combined hormone receptors (P = 0.020), and a complete remission/no evidence of disease status after HDCT (P < 0.001). In patients who had a disease-free interval (DFI) >24 months after primary surgery, an SDIP of >55 U was independently associated with a longer PFS [hazard ratio (HR) = 2.73; 95% confidence interval 1.29-5.81; P = 0.009].
Conclusion: HDCT can achieve long-term PFS in young MBC patients with limited, hormone-responsive and chemotherapy-sensitive disease. After a DFI >24 months, a longer PFS is associated with a higher chemotherapy dose as measured by SDIP. These retrospective analyses suggest SDIP might be a tool for studying cumulative dose as a determinant of outcome of MBC chemotherapy. Thus far, however, we cannot clearly identify any subgroup of MBC patients in whom HDCT with ASCT is of particular benefit.