Expression of a free gamma heavy chain in serum following autologous stem cell transplantation for IgG kappa multiple myeloma

A 41-year-old male with IgG kappa multiple myeloma is described. He developed a free gamma heavy chain without an accompanying light chain following high-dose chemotherapy and autologous peripheral blood stem cell transplantation. The free gamma heavy chain was detected in serum and urine specimens 2 months after transplant, and eventually evolved into an IgG kappa monoclonal protein with electrophoretic properties similar to the original myeloma protein. Although the origin of the free gamma heavy chain remains uncertain, it was most likely related to the underlying plasma cell malignancy and, therefore, was an early sign of disease relapse.