Premalignant Clonal Hematopoietic Proliferations

In situ follicular neoplasia: a clinicopathologic spectrum

AIMS

In situ follicular neoplasia (ISFN) occurs in ≈2-3% of reactive lymph nodes and is currently set apart from "partial involvement by follicular lymphoma" (PFL). ISFN can progress to overt lymphoma, but precise parameters to assess this risk and its association with related diseases remain incompletely understood. This study proposes to explore these parameters.

METHODS AND RESULTS

We reviewed 11 cases of ISFN and 1 of PFL between 2003 and 2018. Ten patients had ISFN in lymph nodes, one in the spleen. H&E and immunohistochemical stains were reviewed. Involvement of follicles by ISFN was scored using a 3-tier scheme. Of 5 cases with low ISFN scores, one had chronic myelomonocytic leukemia, one mycosis fungoides and three were free of hematopoietic diseases. Among them, 4 are alive and one was lost to follow-up. Of the 6 ISFN cases with high scores, 2 had concurrent marginal zone lymphomas, 1 concurrent diffuse large B-cell lymphoma (DLBCL), 1 Castleman-like disease, another progressive transformation of germinal centers with IgG4-related disease, and 1 no hematopoietic disease; all are alive except one who died of concurrent DLBCL. The patient with PFL developed DLBCL 7 years after diagnosis.

CONCLUSIONS

Based on this limited series, we conclude that only cases with high scores are associated with an overt lymphoma or an abnormal lymphoid process, and that scoring may be a useful parameter to assess risk for associated lymphoma, deserving further study. We also carried out a comprehensive review of the literature.

A Tissue Counterpart to Monoclonal B-Cell Lymphocytosis

CONTEXT.—

B-cell clones discovered in tissue biopsies, without overt lymphoma, may represent a tissue counterpart to peripheral blood monoclonal B-cell lymphocytosis (MBL), herein termed tMBL.

OBJECTIVE.—

To characterize the clinicopathologic features of tMBL.

DESIGN.—

During a 10-year period, we retrospectively identified non-bone marrow/peripheral blood cases with monotypic B cells detected by tissue-based flow cytometry, but without an identifiable lymphomatous infiltrate on routine histopathology. We excluded cases with prior diagnosis of chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma or MBL.

RESULTS.—

Fifty-four cases were identified (35 lymph node, 3 splenic, and 16 soft tissue/viscera). Forty-six cases were CLL-type, 2 were atypical CLL, and 6 were non-CLL. tMBL was detectable by immunohistochemistry in 14 cases (26%, all CLL-type). Concurrent blood flow cytometry, available in 10 cases, showed 4 with low-count MBL (3 CLL-type, 1 with non-CLL-type), 5 with high-count MBL (all CLL-type), and 1 case negative for clonal population. With median follow-up of 51 months, 2 patients had progression of disease (CLL, 68.7 months; and diffuse large B-cell lymphoma, 5.9 months). Patients with IHC-detectable tMBL had increased monoclonal B cells per total lymphocyte events (P = .01), morphologic evidence of bone marrow involvement (P = .04), higher white blood cell count (P = .02), and increased absolute lymphocyte count (P = .02).

CONCLUSIONS.—

tMBL spans an immunophenotypic spectrum similar to MBL, is detectable by immunohistochemistry in a minority of cases (often CLL immunophenotype), and is likely systemic in most cases. Development of overt lymphoma is uncommon but may occur, warranting clinical follow-up.