FIRST STEP: 80 yrs woman underwent BM biopsy for NHL staging procedure ("NODAL DLBCL"). After routine screen (CD20, CD3, CD138) I've mentioned CD20+/- (dim) small population, different from CD20+++ small reactive lymphos. Pax-5 and CD79a reveal an interstitial infiltrate of lymphocytes (small- medium caliber) with oval and slightly irregular nuclei.  
IH1: CD23-;Bcl6-;CD20-/+;Pax-5/CD79a+: low grade NHL involvement?  
 
2ND STEP: DLBCL was treated with single chemotherapy course (most probably due to patient age and condition).Primary diagnosis of nodal DLBCL was reviewed. The architecture of node was unusual for ordinary DLBCL creating an impression of "histyocytoma". Vague nodules consist of large-medium sized cc like cells and centroblasts with irregular nuclei with slight spindling.  
IH2: LCA+ 100%, CD79a+ 100%, Bcl2+ 100%, PAX5+ 50%, MUM1+ 50%, CD20+(weak) 20%, Ki67+ ~40%, CD10/CyclinD1/CD30/BCL6/CD34/Tdt/CD138-. Some osteoclasts/giants CD79a+, some CD79a-. CD21/CD23 FDC network is absent. Ig kappa++> Ig lambda+.  
 
PROPOSAL: DLBCL in the node, transformed from low grade lymphoma (MzL), spreading in BM???  
QUESTION: THE DEFINITE NOSOLOGY OF NHL?  
NOTE: NUclear details are briliant in reticulin (GSPS) stain.