Extramedullary (EMP) relapse in unusual locations in multiple myeloma: Is there an association with precedent thalidomide administration and a correlation of special biological features with treatment and outcome?

Extramedullary relapse constitutes an uncommon manifestation of multiple myeloma (MM), characterized by highly malignant histology, special biological features, resistance to treatment and poor outcome. Its incidence has been increased during the last years, probably due to the introduction of novel strategies in the management of MM, including intensified treatment and immunomodulatory drugs. Here we report nine cases of extramedullary relapse of MM, presented in unusual locations, seven of which had previously been treated with thalidomide-containing regimens (TCR). Our aim was to explore the morphological, immunophenotypical, molecular and laboratory characteristics accompanying EMP-relapse and seek possible correlations with treatment and clinical outcome.