CD5 and mantle cell lymphoma: Cervical lymph node biopsy demonstrated diffuse proliferation of medium-sized, abnormal B lymphocytes with an immunophenotype of CD5<sup>+</sup>, CD19<sup>+</sup>, CD20<sup>+</sup>, cyclin D1<sup>+</sup>, SOX11<sup>+</sup>, and κ<sup>+</sup>, with a Ki-67 index of 20%, confirming MCL, stage IV.