Case with translating to multiple myeloma at 8 years after radiation therapy for extramedullary plasmacytoma of the larynx.

We report a case of extramedullary plasmacytoma of the larynx that was eradicated by radiotherapy; however, 8 years later, the disease had progressed to multiple myeloma. A mid -60s Japanese woman presented with a right-sided arytenoid mass in the larynx who underwent biopsy at another hospital. Based on the biopsy results, the patient was diagnosed with extramedullary plasma cell tumour and was referred to the Department of Otorhinolaryngology at our hospital. She received radiotherapy (50.4 Gy) and the laryngeal tumour was eradicated. Positron emission tomography/CT (PET-CT) revealed no abnormal accumulation in the larynx or whole body. After radiotherapy, the department of otorhinolaryngology, in consultation with Ddepartment of haematology performed follow-ups using laryngoscope, blood examination and PET-CT. Five years after the end of radiotherapy, the patient had no local recurrence or transition to multiple myeloma. However, 8 years later, blood examination and PET-CT revealed multiple myeloma. Laryngoscopy did not reveal any recurrent laryngeal tumour. Therefore, chemotherapy for multiple myeloma was administered at the department of haematology. Three months after the initiation of chemotherapy, the accumulation had disappeared in PET-CT. Three years have passed since chemotherapy initiation. At present, no recurrence or metastasis was observed in the larynx or whole body.