Lymph node, In situ follicular neoplasm, CD10 stain

In situ follicular neoplasm, formerly known as follicular lymphoma in situ (FLIS), is defined as the presence of BCL2+/CD10+ neoplastic follicles in a background of reactive germinal centers. The neoplastic follicles are predominately composed of monoclonal centrocytes, which carry the t(14;18) IGH/BCL2 translocation. Given their indolent nature, the name "intrafollicular neoplasia" has been proposed as an alternative terminology. The differential diagnosis of FLIS includes partial involvement of the lymph node by FL (PFL). Studies have shown that only 5% of the patients with FLIS will develop or have concurrent FL; on the other hand 53% of the PFL will progress to FL if left untreated.

Refer to the paper by Jegalian et al for the criteria used to distinguish FLIS from PFL (link in Related Content section).

This slide shows CD10 stain. See Related Content for H&E, BCL2, and BCL6 stains.