The role of T-cell phenotype and T-cell receptor rearrangement in the diagnosis of T-cell malignancies

We read with interest the article by Flammiger et al. [1] on the study of a series of patients with aberrant T-cell phenotype of unclear significance by flow cytometry (FC). They divided their cases into mature T-cell malignancies (TCM) and reactive (non-TCM) cases, focusing on the phenotypes that pose a diagnostic challenge, having excluded those cases whose clinical evolution and further testing did not allow for a clear diagnosis, as well as those cases with obviously aberrant phenotypes. After analyzing their FC reports they argue that an aberrant T-cell phenotype of unclear significance is of little help in the diagnosis of TCM. They only found a correlation with a loss of expression of CD7, more frequent and marked in TCM, but also present in up to 30% of the non-TCM cases (which, notably, included B-cell malignancies in 50% of cases). The authors conclude that, in those cases without an obviously aberrant phenotype, FC can only be a part of a much larger set of diagnostic tools, which include cytogenetics, the study of T-cell receptor (TCR) rearrangements, clinical course and histological examination whenever possible. However, it is well established that TCR clonality is often detected in reactive cases or simply with aging [2–8]. It has been our experience that, indeed, T-cell FC analysis often shows abnormal markers that ultimately do not reflect an underlying TCM [3]. Thus, we set out to analyze the role of T-cell phenotype and TCR rearrangements in the diagnosis of TCM. From October 2007 to December 2014, there were 452 TCR rearrangement studies performed at our institution. After exclusion of all patients who had previously been tested for TCR clonality and those not simultaneously studied by FC, 120 cases were left and were the object of this study. Samples tested were primarily peripheral blood but also bone marrow, lymph node biopsies, lymph node fine needle aspiration and pleural or ascitic exudates. Demographic, clinical and diagnostic data were collected and, based on the FC results, four groups were established: (1) those with an obviously aberrant phenotype, including T-cell expression of CD30, CD10 or CD1a, loss of CD26, expression of gammadelta chains and CD4  CD8 co-expression ( 5% of the lymphocytic population); (2) those with an aberrant T-cell phenotype of unclear significance, as described by Flammiger et al. [1]. In our series, those abnormalities included diminished expression of CD7, CD5 or alpha-beta chains and expression of CD56 or CD57 by T-cells (Table I); (3) those with an abnormal CD4/CD8 ratio, defined as CD4/CD8  3 or CD4/CD8  1; and (4) those with a normal T-cell phenotype in whom TCR rearrangement testing was ordered to study absolute lymphocytosis or lymphopenia. Concerning diagnosis, we divided TCM into aggressive T-cell lymphomas (TCL), i.e. those high-grade lymphomas that required chemotherapy, including Sézary syndrome (SS), all diagnosed by histological tissue examination, and indolent TCM, which in our series were limited to T-cell large granular lymphocyte leukemias (TLGL), diagnosed by peripheral blood smear and according to WHO criteria. We diagnosed as reactive those cases that were clearly related to a non-hematological disorder as well as those that eventually resolved, even without a specific diagnosis. Cases with unclear clinical course and diagnosis were excluded and labeled as unclassified There were 20 patients in group 1, 17 (85%) of them with a clonal TCR, 23 patients in group 2, 15 (65%) of them with a clonal TCR, 47 patients in group 3, 18 (38%) of them with a clonal TCR and 30 patients in group 4, 6 (20%) of them with a clonal TCR (p  0.001). Table I shows for each of the phenotype groups the number of TCM, non-T-cell hematological malignancies (mostly B-cell lymphomas), non-malignant hematological disorders (mostly bone marrow aplasia) and reactive cases. Of note, not only do clearly aberrant phenotypes almost always reflect a hematological disorder (mostly TCL, but also TLGL or B-cell malignancies), but TCL and SS were mostly found in the group with clearly aberrant phenotypes (9/11 and 3/6, respectively). However, TLGL were found in all four groups. Furthermore, aberrant phenotypes