New patterns of relapse in multiple myeloma: a case of "light chain escape" in which FLC predicted relapse earlier than urine and serum immunofixation.

Multiple myeloma (MM) is characterized, in about 80% of cases, by the production of monoclonal intact immunoglobulin and more than 95% of them have elevated concentrations of involved (i.e. of the same class of intact immunoglobulin) free light chain (FLC). The introduction of novel therapeutic strategies has changed the natural history of the disease, leading to new manifestations of relapse. Light chain escape (LCE) is a pattern of relapse in which the FLC increase is not accompanied by a concomitant raise of the original monoclonal component (MC). Here we present a case of a 55-year-old man with an IgG kappa MM stage III diagnosed in September 2007. At presentation an IgG kappa MC and urine Bence Jones protein (BJP) kappa were present. Bone marrow biopsy (BMB) showed the presence of 80% monotypic kappa plasma cells (PCs). The patient received bortezomib, thalidomide, dexamethasone before undergoing a double autologous stem cell transplantation (ASCT) in October 2008 and April 2009. In May 2011 he relapsed showing the same pattern of presentation and treatment with lenalidomide and dexamethasone was started. ln May 2013 serum and urine immunofixation and FLC became negative. In September 2014, an increase of kappa FLC was observed, while serum and urine immunofixations remained negative until January 2015, when urine immunofixation became positive. Eventually, in February 2015, serum immunofixation revealed the presence of a free kappa MC. After a new BMB showing 80% of monotypic kappa PCs, a LCE relapse was diagnosed and the patient started the treatment with bendamustine, bortezomib and dexamethasone. In the present case, the increase of kappa FLC has indicated relapse 4 and 5 months earlier than urine and serum IFE, respectively. Our observation confirms that it is advisable to routinely perform FLC or BJP during follow up of MM patients undergoing ASCT and/or treatment with biological drugs to ensure that LCE is not missed.