Composite Lymphoma Comprising Follicular Lymphoma with In-situ Mantle Cell Neoplasia: A Case Report and Review of the Literature

A 55-year-old gentleman presented to our hospital with a single inguinal adenopathy, and no other clinical symptoms or signs. An excisional lymph node biopsy was performed. Pathologic evaluation demonstrated follicular center site which stained positive for CD20, CD10, Bcl-2, Bcl-6, and mantle zone cells which demonstrated Cyclin D1 (CCND1) positivity, partial SOX11 positivity and no expression of CD5, suggesting the diagnosis of composite lymphoma comprising follicular lymphoma (FL) with in situ mantle cell neoplasia (ISMCN), the latter previously referred as in situ mantle cell lymphoma (MCLIS). FL is known as indolent non-Hodgkin lymphoma; however, the clinical significance of a coexisting ISMCN continues to be elusive, and optimal management of these patients remains largely unknown. This paper reports a new case of this extremely uncommon condition and also discusses reviews of the literature including advances in molecular pathogenesis and lymphoma genomics with the aim to offer novel insights into this rare hematological malignancy.