Allogeneic transplantation for multiple myeloma: late relapse may occur as localised lytic lesion/plasmacytoma despite ongoing molecular remission.

Allogeneic SCT for myeloma may be curative for young patients, but its role remains controversial because of a reported high TRM in some series. Since 1991, we have performed 25 allografts for myeloma using fully matched sibling donors. Of the 18 evaluable patients, 13 achieved CR at a median time of 2.5 months post-transplant. The five patients who were not in CR when assessed at 3 months received a short course of alpha-interferon and four subsequently achieved CR with this approach at a median of 82 days. One patient who failed to respond to IFN went on to achieve CR after four doses of DLI therapy, thus giving an overall CR rate of 72%. Seven patients have relapsed at a median of 4.7 years post-transplant (range 1.38-7.7 years) including two patients who had received IFN therapy. In five of these cases, relapse has been as a localised area of bone disease or isolated plasmacytoma with no evidence of marrow involvement by trephine biopsy or molecular analysis. All patients with localised relapse were treated with local radiotherapy +/-DLI and four are currently disease free despite two patients having had further treatment for a second localised lesion. Six patients died of TRM (24%) and the OS at 8 years is currently 69% with an EFS of 26%. These results suggest that allogeneic SCT for myeloma can be carried out with an acceptable TRM and a high CR rate. However, late relapses as localised disease may be a frequent finding and may represent foci of myeloma not eradicated by the conditioning. The use of pretransplant MRI scanning and top-up radiotherapy to involved areas may be useful in preventing this type of relapse.