Unusual Clinical Presentation of B-Cell Prolymphocytic Leukemia Cases as Splenic Marginal Zone Lymphoma Effectively Treated With Rituximab Monotherapy.

Background/aim: B-cell prolymphocytic leukemia (B-PLL) is a rare B-cell neoplasm, historically classified as a distinct entity, but recently removed from the World Health Organization (WHO) classification due to its overlap with other B-cell chronic leukemic lymphoproliferative disorders (B-CLD). We describe five cases that met the classical peripheral blood criteria for B-PLL but exhibited clinicopathological features identical to splenic marginal zone lymphoma (SMZL). This study highlights the diagnostic challenges and treatment outcomes of these cases, emphasizing the need for reconsidering their classification.

Patients and methods: We retrospectively analyzed five patients diagnosed with B-PLL between 2008 and 2014. Clinical, hematological, biochemical, morphological, immunophenotypic, immunohistochemical, and molecular characteristics were assessed. Bone marrow aspirates, biopsies, and immunohistochemical staining were performed, and cytogenetic analysis was conducted to identify key molecular markers. All patients received Rituximab monotherapy, following the standard treatment protocol for SMZL.

Results: All patients presented with marked prolymphocytosis (>55% circulating lymphoid cells) and massive splenomegaly. Immunophenotypic and bone marrow histologic findings were consistent with SMZL, with a characteristic intrasinusoidal infiltration pattern. Cytogenetic studies revealed the absence of MYC rearrangements and TP53 deletions, with one case exhibiting a 7q31 deletion, a hallmark of SMZL. Rituximab monotherapy was highly effective, leading to complete remission in two patients and prolonged responses in all but one case.

Conclusion: These findings suggest that a subset of cases diagnosed as B-PLL based on blood morphology may represent a variant of SMZL with prolymphocytic morphology. The excellent response to Rituximab further supports this hypothesis. Our study reinforces the need for reclassification of such cases within the spectrum of SMZL rather than a separate entity.