Peripheral T cell lymphomas with follicular T helper phenotype: a new basket or a distinct entity? Revising Karl Lennert's personal archive.

AIMS: To revise 25 cases selected from Karl Lennert's personal archive (21) and Bologna and Frankfurt Registries (four) because of cytological similarities. METHODS AND RESULTS: All cases were provided with paraffin blocks and studied by immunohistochemistry and molecular techniques. While phenotyping was very informative, among molecular studies only EBER in situ-hybridization (ISH) was successful. Twenty-two cases were concluded as peripheral T cell lymphomas (PTCL). Of these, six were reclassified as angioimmunoblastic T cell lymphoma (AITL), 13 as PTCL, not otherwise specified (NOS), including four follicular variants and one tumour with T-zone pattern, and three as borderline tumours between AITL and PTCL/NOS. All these cases consisted homogeneously of small/medium-sized elements with mild nuclear atypia and an evident rim of clear/pale cytoplasm. On immunohistochemistry, they regularly expressed three to six follicular helper T cell (FTH)-associated markers. EBER-ISH revealed scattered EBV-infected B cells in all tumours except those with 'follicular' growth pattern. The content of follicular dendritic cells and high-endothelial venules varied significantly depending on the histotype. CONCLUSIONS: This study shows that: (i) historical material can be still employed usefully, and (ii) the FTH-phenotype corresponds to a broad spectrum of PTCLs that might form a new category to be validated in future molecular and clinicopathological analyses.

Follicular lymphoma: still Six characters in search of an author?

Follicular lymphoma (FL) is regarded as a distinct entity in the literature as well as in the 2008 edition of the WHO classification of tumours of haematopoietic and lymphoid tissues. Nevertheless, there are still several issues that are matters of controversy such as the grading system or the exact biological location of grade 3B FL. This makes FL somewhat like the Six characters in search of an author of Pirandello's comedy. Here, we revise the morphology and pathobiology of FL by highlighting both the areas remaining critical and future perspectives. This review was inspired by the reappraisal of Professor Lennert's personal archive that represents a unique legacy for the entire scientific community.

Morphological variability of lymphohistiocytic variant of anaplastic large cell lymphoma (former lymphohistiocytic lymphoma according to the Kiel classification).

According to the WHO classification, anaplastic large cell lymphoma (ALCL) is a distinct T-cell lymphoma entity with a number of morphological variants. The characteristic feature of lymphohistiocytic variant of ALCL according to the WHO classification is the abundance of histiocytes that exceed and mask the tumour cell population. In the current, study we reanalysed a historical series of 17 lymphomas, diagnosed as lymphohistiocytic lymphoma according to the criteria of the Kiel classification, with the presence of large purple macrophages (LPM) as the decisive finding for diagnosing this lymphoma subtype. We assessed the cellular composition of the tumour and correlated the results with the definition of lymphohistiocytic variant of ALCL given in the WHO classification. Although all cases in our cohort matched the criteria of ALCL according to the WHO, in 30% of the cases, the total amount of macrophages did not exceed the number of CD30-positive tumour cells. Our results indicate that the presence of LPM might be helpful to identify this subgroup of ALCL. Because the distinction of morphological subtypes of ALCL is of clinical relevance, improved criteria for subtyping ALCL are urgently needed that might include the presence LPM as one criteria.