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WHO Classification of Tumours
Intrafollicular neoplasia/"in situ" follicular lymphoma
Tumours of haematopoietic and lymphoid tissues


This is a variant of follicular lymphoma (FL) . Cases occur in which architecturally normal-appearing lymph nodes and other lymphoid tissues have one or more follicles that demonstrate BCL2-overexpressing centrocytes and centroblasts, with or without a monomorphic cytologic appearance suggestive of follicular lymphoma
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Cong P, Raffeld M, Teruya-Feldstein J, Sorbara L, Pittaluga S, Jaffe ES (2002)
In situ localization of follicular lymphoma: description and analysis by laser capture microdissection.
Blood 99: 3376-82

. Some of these patients are found to have follicular lymphoma elsewhere, either before or simultaneously, some develop overt FL later, and others have remained without evidence of FL. In patients with overt FL elsewhere, this phenomenon likely represents colonization of pre-existing follicles by neoplastic follicle centre cells. In patients without known FL, the significance of this phenomenon is difficult to ascertain. It may represent the tissue counterpart of circulating clonal B cells with BCL2 rearrangement —that is, a clone of cells that have the translocation but not the other genetic abnormalities to result in overt progressive malignancy, or in some cases it may represent the earliest evidence of a true follicular lymphoma that will progress to overt lymphoma. This phenomenon cannot be recognized without BCL2 staining. The pathology report should indicate that the significance of the finding is unknown, and that clinical evaluation for evidence of overt FL elsewhere is suggested.

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Introduction: Classification of lymphoid neoplasms