Multiple myeloma (MM) patients live longer due to more effective treatment, and we now see previously uncommon manifestations of MM, like extramedullary disease. We present a case of a 74-year-old man known with MM that relapsed with extramedullary manifestations at different locations. One of them as a gastric plasmacytoma (GP). He was successfully treated with chemoradiotherapy (Daratumumab, Bortezomib and Dexamethasone), which resulted in clinical response for 8 months, confirmed by biopsy and histopathology. Perforation of the GP occurred, and he underwent partial gastrectomy (Billroth II gastrojejunostomy). The patient's disease progressed again 5 months after surgery, and he did not want any additional treatment. He accepted palliative care and died 10 months after the operation. A lack of knowledge about the characteristics and treatment of extramedullary MM exists, and prospective studies to investigate incidence, prognosis and treatment for extramedullary MM are needed for improving the poor prognosis of this manifestation.