Figure 3

Histological presentation of a primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder (SMLPD, case no 7). (A) Clinical presentation as an infiltrated erythematous-squamous plaque of the left breast; (B) (Hematoxylin–Eosin-Saffron (HES), ×1.5), (C,D) (HES, ×20): lichenoid pattern constituted of atypical cells, small-medium sized; (E) (CD4, ×10) and (F) (CD20, ×10): slight predominance of T-cells (60%), with a CD2+ CD5+ CD7+ phenotype, and a significant predominance of CD4+ T-cells (75%) instead of CD8+ T-cells (25%). (G) (CD138, ×10): very few associated plasma cells (black arrow), which were polytypic for kappa and lambda, and located outside of the proliferation in this particular case, but scattered among T-cells in most SMLPD cases; (H) (PD1, ×20), (I) (CXCL13, ×20), (J) (BCL6, ×20) and (K) (CD10, ×20): huge expression of TFH markers except for CD10 which was negative (PD1 90%, CXCL13 40%, BCL6 25%). As illustrated, PD1 expression shows a higher intensity in medium/large cells, and some PD1+ cells also tended to form “rosettes” around large lymphocytes (insert). Proliferative index using Ki67/Mib1 was evaluated a 15%, and no follicular dendritic cells network (pictures not shown). The diagnosis of SMLPD was confirmed thanks to molecular data; the presence of a monoclonal T-cell population. This case displayed an isolated TET2 pathogenic variant using TNGS.