Overlapping morphologic and immunophenotypic profiles in small B-cell lymphoma. A report of two cases

Early lymph node involvement by mantle cell lymphoma limited to the germinal center: report of a case with a novel "follicular in situ" growth pattern

Recently, several reports have described cases of "in situ" mantle cell lymphoma (MCL) in which scattered cyclin D1+ cells were present within the mantle zones of reactive-appearing lymphoid follicles. In this report, we describe an unusual histologic pattern of in situ MCL that was identified in a staging lymph node for colonic adenocarcinoma resected 4 years before a diagnosis of symptomatic MCL. Retrospective immunohistochemical studies showed scattered cyclin D1-expressing cells within otherwise reactive germinal centers but not in the surrounding mantle zones. The presence of early MCL cells limited to reactive germinal centers represents a novel "follicular in situ" growth pattern for MCL, which overlaps morphologically with reactive follicular hyperplasia and follicular lymphoma and which could have implications for MCL pathogenesis.

How I treat: diagnosing and managing "in situ" lymphoma

The "in situ" lymphomas are often incidental findings in an otherwise reactive-appearing lymph node. Notably, the risk of progression to clinically appreciable lymphoma is not yet fully known. The diagnosis of "in situ" lymphoma is feasible when immunohistochemical characterization is carried out and genetic abnormalities are assessed. "In situ" follicular lymphoma is characterized by the presence within the affected germinal centers of B cells that strongly express BCL2 protein, a finding that supports their neoplastic nature, in the absence of interfollicular infiltration. In "in situ" mantle cell lymphoma, the lymphoma involvement is typically limited to the inner mantle zone, where lymphoma cells are cyclin D1(+) and weakly BCL2(+), CD5(+). A staging workup to exclude other site of involvement is highly recommended for the possible coexistence of an overt lymphoma. Biopsy of all sites of suspicious involvement should be mandatory. No evidence for starting therapy also in the presence of multifocal "in situ" lymphoma exists, and a "wait-and-see policy" is strongly suggested. A follow-up strategy reserving imaging evaluation only in the presence of disease-related symptoms or organ involvement appears to be a reasonable option. For patients with concomitant overt lymphoma, staging and treatment procedures must be done according to malignant counterpart.