Syngeneic hematopoietic stem cell transplantation for women with metastatic breast cancer.

Metastatic breast cancer has been a common indication for autologous hematopoietic stem cell transplantation (HSCT). Previous reports indicate 3-year survival and progression-free survival (PFS) rates after autotransplant to be about 30 and 15%, respectively. Most deaths are from recurrent disease. One potential cause for high relapse rates is graft contamination with tumor. We describe 14 women with metastatic breast cancer transplanted between 1991 and 1998 with hematopoietic cells from identical twins. Median age was 41 y (range 34-50). Most women (12 of 14) were treated with mastectomy, and all received anthracycline-based regimens in their pretransplant course; nine women also received a taxane, seven radiotherapy and three hormonal therapy. Four women were in complete remission (one CR, three CRU) at transplant, five were in partial remission, two had stable disease and two had progressive disease. Eight women have died, one of treatment-related causes and seven of progressive breast cancer. Three-year survival was 48% (21-71%) and 3-year PFS was 21% (5-45%). Although the number of patients is small, outcomes for women transplanted with syngeneic grafts are similar to those of women receiving autologous grafts. This suggests that residual cancer in the patient is the major contributor to relapse after transplantation for breast cancer.