A plasmacytoma is a myelomatous mass that can develop into a widespread illness, be seen alone, or be combined with multiple myeloma (MM). Bone marrow does not always indicate MM, but over the course of 4-5 years, about 50% of cases advance to this disease. In this study, we aimed to present a patient who was diagnosed with multiple myeloma and developed giant plasmacytoma despite bone marrow response during follow-up.

During the 4th cycle, a giant plasmacytoma developed at the patient's right arm proximal humerus level.Ultrasound imaging performed on the right upper extremity was reported as 'Diffuse skin-subcutaneous thickness, increased echogenicity and linear fluid areas were observed. A large 5 × 3 cm hypoechoic nodular lesion with markedly increased blood flow was observed in the proximal medial neighborhood of the patient's incision line. Plasmacytoma continued to shrink with radiotherapy and chemotherapy

At the time of diagnosis, EPs are seen in around 7% of individuals with MM and are best identified by PET/CT scans; the presence of EP is linked to a worse prognosis. Later in the course of the disease, 6% more patients will get EP. Large, crimson-colored, subcutaneous masses can be a symptom of EP. The creases on the palms and/or soles may be affected by plane xanthomas, which may be a paraneoplastic condition. Rarely, cutaneous spicules made partially of the monoclonal (M) protein may form.

Results

We presented a case that developed a giant plasmacytoma based on multiple myeloma. This case is important because, after the diagnosis, a giant plasmacytoma developed during the 4th cycle of chemotherapy, although the patient's laboratory examinations and clinic responded to chemotherapy after 3 cycles of chemotherapy.