Late Relapse of Multiple Myeloma with Testicular Plasmacytoma after Autologous Hematopoietic Stem Cell Transplantation: A Case Report and Review of the Literature.

High-dose chemotherapy combined with autologous hematopoietic stem-cell transplantation (ASCT) is the first-line treatment for multiple myeloma. Yet, some patients will relapse. Testicular plasmacytoma which rarely happens can be isolated or associated with progressive multiple myeloma. Here, we report a case of multiple myeloma (MM) undergoing ASCT when the patient obtained complete remission. He developed painless right testicular swelling after nearly 3 years since the ASCT. After radical orchiectomy, histopathology showed diffuse abnormal plasma cells infiltration of the testicular tissue. At the same time, he experienced a bone marrow relapse, and relapse of multiple myeloma with plasmacytoma of testis was confirmed. It is also important to note that at the time of initial diagnosis with MM, he had no mutation of TP53 and MYC in FISH, but at a relapse with testicular plasmacytoma, some high-risk karyotypes were detected, including amplification with 1q21 and absence of p53, RB1/D13S319 and rearrangement with IGH. Similarly, the rearrangement with IGH was found in the histological sections of testicular neoplasm by FISH. The clinical characteristics and altered chromosomes of the case are discussed in the context of previous reports. In common with reports, testicular plasmacytoma with relapsed multiple myeloma had a worse outcome and our findings suggest that chromosome monitoring can be added in multiple myeloma after ASCT.