Supplementary Material for: Isolated non-secretory extramedullary relapse of multiple myeloma responded completely to localized radiotherapy

INTRODUCTION: Non-secretory multiple myeloma (NSMM) is a rare form of multiple myeloma (MM) that is often difficult to detect and has not yet been well characterised. This is due to the lack of production or the presence of monoclonal proteins levels below levels detectable by testing such as serum/urine electrophoresis (SPEP/UPEP) and immunofixation.
CASE PRESENTATION: Two patients of ours were being treated for MM with typical courses of systemic therapy. By the 3rd line therapy, both developed an extramedullary mass, one in the pelvis and the other in the neck. In both cases blood work showed no measurable monoclonal protein (MP), normal free light chain levels and unremarkable skeletal surveys. Secondary malignancies were suspected due to the clinical presentation in each case, and biopsies confirmed the presence of non-secretory plasmacytomas. Both patients were only treated with localized radiotherapy with a total dose of 2000 cGy in 5 fractions over 1 week. Ultimately, this resolved the original masses with no residual tumours. No changes had to be made to their systemic therapies, and both patients remain stable in remission.
CONCLUSION: Non-secretory multiple myeloma relapse is not unusual and should be suspected in patients with relapsed refractory disease. Relapse should be confirmed by a tissue biopsy, and secondary malignancies should be ruled out. Radiotherapy is an excellent option to treat localized relapse and preserve the current line of systemic anti-myeloma therapy.