From carcinoma through lymphoma to myeloma: a gastric mass diagnostic rollercoaster ride.

We describe a dramatic clinical presentation of extramedullary multiple myeloma (MM) in an elderly patient with known monoclonal gammopathy of unknown significance (MGUS). Gastrointestinal symptoms and a gastric mass on imaging studies suggested an advanced solid gastric malignancy. Pathological workup of gastric biopsies first suspected a lymphoma, a second opinion finally confirmed an extramedullary MM. Treatment with bortezomib, cyclophosphamide and dexamethasone induced rapid relief of symptoms and normalisation of renal function as well as serum MM markers. Our case highlights the diagnostic difficulties when MM presents with signs and symptoms of respective end-organ involvement rather than typical 'CRAB' criteria. It underlines the importance of actively considering MM in a patient with MGUS, regardless of the clinical presentation of a specific medical problem. Our report also impressively illustrates the rapid response of MM and its gastric extramedullary manifestation to guideline-adherent chemotherapy.