Indolent mantle cell leukemia: a clinicopathological variant characterized by isolated lymphocytosis, interstitial bone marrow involvement, kappa light chain restriction, and good prognosis

Abstract

Background: Cases of mantle cell lymphoma with indolent behavior have been reported, but are poorly identified by current clinical risk models. Early studies found peripheral blood involvement to be an adverse prognostic factor; however, cases of a seemingly indolent variant of mantle cell lymphoma, characterized by peripheral blood involvement and minimal nodal disease, have been incompletely described, particularly with regard to bone marrow findings. We report a series of leukemic phase mantle cell lymphomas with a non-progressive or slowly progressive course.

Design and methods: Cases presenting with mantle cell lymphoma limited to the peripheral blood/bone marrow from 2000-2010 were identified. Diagnoses were established by morphology, flow cytometric analysis and requisite evidence of IGH-CCND1@ by fluorescence in-situ hybridization or t(11;14)(q13;q32) by cytogenetics. Patients with lymphadenopathy, splenomegaly and gastrointestinal symptomatology were excluded.

Results: Patients (n=8, median age 60.5 years) were asymptomatic with mild lymphocytosis (8.7×10(9)/L; range, 4.5-14.2×10(9)/L) and cytology typical of mantle cell lymphoma. Flow cytometric analysis showed that all expressed CD5, CD19, CD20, variable CD23, and a striking kappa immunoglobulin light chain restriction (7/8 cases). Bone marrow biopsy at diagnosis showed interstitial single or small lymphoid aggregates with similar patterns of CD20 and cyclin D1 immunostaining which were not readily discernable by hematoxylin and eosin stain. SOX11 was negative (4/5) or only weakly expressed (1/5). The median follow-up was 27 months (range, 5-109 months) and all patients, but one, are alive with no clinical evidence of disease. The prevalence of indolent mantle cell lymphoma presenting only with lymphocytosis, among all mantle cell lymphomas diagnosed during the same period, was 3%.

Conclusions: Leukemic mantle cell lymphoma limited to blood and bone marrow is an indolent variant characterized by mild-moderate lymphocytosis, interstitial low-level bone marrow involvement, simple karyotype, kappa light chain expression, cyclin D1 expression with lack of SOX11, and slow or absent clinical progression. Some cases may represent a mantle cell lymphoma counterpart to chronic lymphocytic leukemia - phenotype monoclonal B-cell lymphocytosis. Recognition of this variant could inform treatment decisions and possibly avoid unnecessary treatment.

Figure 1.

Spectrum of peripheral blood morphologies. (A-B) Classic type with high nuclear:cytoplasmic ratios, slight nuclear clefts or irregularities and hyperchromatic condensed chromatin. (C) Small cell or chronic lymphocytic leukemia-like morphology. (D) One case had prolymphocytic morphology. Wright’s stain, Olympus BX50F4, oil immersion, magnification x 1000 A-C, magnification x 500, D; colors corrected after acquisition with Adobe photoshop.

Figure 2.

The predominant bone marrow pattern of involvement for indolent mantle cell leukemia patients. No infiltrates are readily discernable on hematoxylineosin stain (A, D) (Olympus BX50F4, magnification x 200, colors corrected after acquisition with Adobe photoshop), but immunostaining showed interstitial involvement by scattered single lymphocytes with a similar patterns of CD20 (B, E) and cyclinD1 (C, F) immunostaining, estimated at 1% of bone marrow cellularity (magnification x 200–1000, Discovery, Ventana Medical Systems). Patient n. 4 (G) had small interstitial lymphoid aggregates with numerous cyclinD1–positive lymphocytes (Olympus BX50F4, magnification x 200, Discovery, Ventana Medical Systems). Double immunolabeling for CD20/SOX11 (H) shows positive co-expression of SOX11 (red nuclear stain) at a low level in approximately 10% of B cells indicated by CD20⁺ brown cytoplasmic staining (Olympus BX50F4, magnification x 400).