(A) Serum protein electrophoresis showing an M band. (B) Lymph node biopsy showing large atypical lymphoid cells with irregular contours, brisk mitoses, and prominent nucleoli (hematoxylin and eosin, ×400), which were positive for CD20, MUM-1, and Ki-67 (70%) and negative for CD138. (C) Bone marrow biopsy showed lymphoid cells in a diffuse and nodular pattern (hematoxylin and eosin, ×200), which were CD20 and kappa positive and lambda negative.