Minimum diagnostic criteria for plasmablastic lymphoma of oral/sinonasal region encountered in a tertiary cancer hospital of a developing country

Background:  Haematolymphoid tumours other than plasmablastic lymphoma (PBL) may reveal plasmablastic differentiation with overlapping immunoreactivity causing diagnostic dilemma. Elaborate ancillary diagnostic techniques can make the process expensive, tedious and out of reach for pathology laboratory in a developing country.
Methods:  Out of 98 total cases of primary non-Hodgkin's lymphoma and plasmacytoma of oral-sinonasal region recorded in our institute over 4 years, 39 cases showing varied plasmablastic differentiation were selected. Morphological and immunohistochemical criteria were applied to identify minimum diagnostic criteria for PBL. Human Immunodeficiency Virus (HIV) correlation and Epstein–Barr virus expressed RNA (EBER) in-situ hybridisation studies were also performed.
Results:  Minimum morphological criteria required to diagnose PBL were: (1) predominant population of plasmablasts which are large monomorphic cells with high nuclear-cytoplasmic ratio, moderate amount of amphophilic cytoplasm and round nucleus with prominent central nucleolus, (2) high mitotic and/or apoptotic index and (3) absence of neoplastic plasma cells in the background. Essential diagnostic immunophenotype consisted of CD20 negativity, LCA +/−, CD138/VS38c diffuse positivity, light chain restriction and high MIB-1 index (>60 %). Twenty-five of the total 32 PBL cases thus identified, involved oral cavity. Of these, 84% affected gingivo-buccal complex. Twenty-eight cases were HIV positive. EBER positivity confirmed the diagnosis in all the HIV-negative cases.
Conclusions:  A triad of 'rapidly growing lesion with predilection for oral mucosa, classical plasmablastic morphology and limited immunohistochemical panel' can render a reliable diagnosis of PBL, irrespective of HIV and EBV status, especially in developing countries with limited resources.