Multifocal in situ mantle cell neoplasia of the ileocecal region: a case report with simultaneous nodal and extranodal involvement.

In situ mantle cell neoplasia (ISMCN) is a rare entity of disputed clinical significance. We report an additional case, unusual by its presentation in the large intestine and its multifocal involvement of several nodal and extranodal sites. The diagnosis was made in a 46-year-old male patient from a surgical specimen resected for cecal adenocarcinoma. Gross examination showed multiple small polypoid lesions surrounding the ileocecal valve, corresponding to lymphoid aggregates with hyperplastic follicles. Numerous cyclin D1/SOX11+ lymphoid cells, harboring the t(11;14)(q13;q32) translocation, were present in the inner layers of mantle zones. The same lesions were found in the ileum, the appendix, and the regional lymph nodes. The final diagnosis was multifocal ISMCN of the ileocecal region, with both nodal and extra-nodal involvement. A simple surveillance was decided. Our observation expands the clinical spectrum of the disease and underlines the necessity to closely examine even normal-appearing reactive lymphoid tissues.

An overlapping case of in situ mantle cell neoplasia and leukemic non-nodal mantle cell lymphoma.

In situ mantle cell neoplasia (isMCN) and leukemic non-nodal mantle cell lymphoma (nnMCL) are classified as an indolent subtype of mantle cell lymphoma (MCL). The tumor cells of isMCN are restricted to the inner layer of the lymphoid tissue mantle zone, exhibiting an in situ pattern histologically. On the other hand, nnMCL is distributed in the peripheral blood, bone marrow and sometimes the spleen, but lymphadenopathy or systemic organ involvement is rare. We report a case of isMCN in a submandibular lymph node resected from a 65-year-old Japanese male. The tumor cells were positive for cyclin D1 (CCND1) and SOX11 expression, and were restricted to the mantle zone area of the lymph node. However, tumor cells were also detected in the stomach mucosa, bone marrow tissue and peripheral blood, suggesting nnMCL. isMCN and nnMCL may have a partly overlapping disease spectrum, although the correlation between these two subtypes has not been well described. This present case demonstrated characteristics overlapping between isMCN and nnMCL.

Early Events in Lymphoid Neoplasms and Indolent Follicular Lymphomas.

Technical advances in diagnostic modalities have led to the characterization of indolent lymphoid disorders similar to the in situ lesions described in epithelial malignancies. These early and indolent lymphoid lesions share clinicopathologic characteristics with well-characterized lymphoid malignancies such as chronic lymphocytic leukemia and follicular lymphoma. The in situ lesions have an indolent clinical course with only a minor subset shown to progress to frank malignancies. In addition to the in situ lesions, new indolent lymphoproliferative disorders have been recently characterized. Diagnosis and characterization of these indolent lesions is necessary to prevent overtreatment with aggressive therapeutic regimens.

In situ neoplasia in lymph node pathology.

In situ neoplasia represents the earliest form of malignant progression and is characterized by localization limited to the compartment corresponding to the cell of origin. Like other cancers, lymphoid neoplasms are considered to develop by multistep pathogenetic mechanisms. However, because of the circulating nature of lymphocytes, in situ lymphoid neoplasia may be difficult to identify histopathologically, and the compartment to which it is restricted may be physiological rather than strictly anatomical. The 2016 WHO classification of lymphoid neoplasms recognizes two in situ entities: in situ follicular neoplasia (ISFN) and in situ mantle cell neoplasia (ISMCN). This review summarizes the clinical features, histopathology, genetics, and differential diagnoses of these two entities, including distinction from both their overly malignant counterparts and a variety of reactive processes.