Multiparameter flow cytometry in the differential diagnosis of aberrant T-cell clones of unclear significance

ABSTRACT Immunophenotypic distinction between neoplastic and reactive T-cell clones can be challenging as peripheral T-cell lymphomas (PTCL) lack an immunophenotypic marker of clonality. Systematic screening of 10,510 cases analyzed by immunophenotyping at our institution between 2006 and 2012 resulted in 49 cases with aberrant T-cell populations of unclear significance. Review of patient charts allowed to assign these cases to three categories: In 21 cases, PTCL could later be confirmed by complementary diagnostics ("PTCL group"). In 20 cases, follow-up confirmed the reactive nature of the aberrant T-cells ("non-PTCL group"). Eight cases remained of unclear significance. Neither the population size nor the number of aberrant markers differed significantly between the PTCL and non-PTCL group. Only loss of CD7 was found significantly more often in PTCL than in non-PTCL patients (p=0.037). Our data shows that aberrant T-cell populations need to be interpreted in the clinicopathological context, as reactive and neoplastic phenotypes largely overlap.