[Blastoïd mantle cell lymphoma, TdT-positive: Toward a more juvenile profile?].

Mantle cell lymphoma is a B-cell lymphoma that occurs predominantly in individuals over 65 years of age and accounts for approximately 2-10% of all B-cell lymphomas. Two forms of the disease are recognized: the classical nodal mantle cell lymphoma and the non-nodal form, the later being often leukemic and SOX11-, with differences at the clinical, immunohistochemical, and molecular levels. The main validated prognostic factors in mantle cell lymphoma include morphology, the Ki-67 proliferation index, and presence of TP53 mutations and/or immunohistochemical expression of the p53 protein. Clinically, the prognosis of patients with mantle cell lymphoma has markedly improved with the introduction of Bruton's tyrosine kinase inhibitors (BTKi), anti-CD20 monoclonal antibodies, and immunotherapies. We report a 63 year-old man with bone marrow involvement by mantle cell lymphoma displaying an immunohistochemical profile CD20+, CD5+, cyclin D1+, SOX11-, with distinctive features including blastoid morphology, diffuse TdT expression, and MYC gene rearrangement. This exceptional association of blastoid morphology, TdT expression, and MYC rearrangement in mantle cell lymphoma suggests a process of tumor dedifferentiation and broadens the clinico-biological spectrum of mantle cell lymphoma, raising significant diagnostic and prognostic challenges.