A 23-year-old female patient presented with abdominal lymphadenopathy, severe hypercalcemia, leukocytosis (54.9x10⁹/L), mild anemia, and normal platelet count. Peripheral blood smear showed 40% atypical lymphoid cells with convoluted nuclei (Figure 1). Flow cytometry analysis performed in the peripheral blood revealed an abnormal population of memory CD4+ T cells (CD5+/-, CD3+/-, CD7-, CD45RO-, CD25-), compatible with Sézary cells. However, serology for human T-cell lymphotropic virus type 1 (HTLV-1) was positive, the diagnosis of CD25-negative ATLL being established.
 

ATLL is a rare peripheral T-cell lymphoma that occurs in about 5% of HTLV-1 carriers from endemic regions, after a long latency period⁽¹⁾. Four clinical subtypes of ATLL with different clinical courses are described: smoldering, chronic, acute leukemic, and lymphomatous⁽¹⁾. Morphologically, typical ATL cells display polylobulated nuclei, being recognized on smears as “flower cells”⁽²⁾. ATLL neoplastic lymphocytes originate in CD4+ helper T cells that share the CD25+ phenotype with regulatory T cells⁽³⁾. Nevertheless, a lack of CD25 expression was reported in a subset of ATLL cases⁽⁴⁾.