In Situ Follicular Lymphoma and Partial Lymph Node Involvement by Follicular Lymphoma: Comparisons, Composites, and Clinical Correlations
AG Jegalian, FC Eberle, S Pittaluga, M Raffeld, ES Jaffe. National Cancer Institute, Bethesda, MD
Background: In situ follicular lymphoma (FLIS) and partial involvement by follicular lymphoma (PFL) may have similar features, with reactive germinal centers present in the lesional lymph node (Blood 99:3376-82, 2002). Their clinical significance has not been well-documented.
Design: FLIS (n = 27) and PFL (n = 52) cases were identified and histopathologic criteria described for distinguishing them. In addition, 4 instances of composite lymphoma comprising FLIS and either Hodgkin lymphoma or B-cell non-Hodgkin lymphomas were identified. Immunohistochemistry included stains for BCL-2, CD20, CD3, and CD10. Clinical follow-up was obtained for the majority of cases.
Results: In FLIS, the lymph node architecture is intact, with well-defined mantle zones; the atypical centrocyte-like cells confined to the follicle centers are typically strongly and uniformly positive for both BCL-2 and CD10. 2 cases (7%) with such features had synchronous follicular lymphoma (FL) at another site, and another 2 (7%) had prior FL. In PFL, the follicles are typically larger, the mantles more disrupted, and the lymph node architecture may be focally altered. All cases except for 2 were low-grade FL (WHO 2008). Among the PFL cases, 13 (25%) were associated with synchronous FL (n = 10) or diffuse large B-cell lymphoma (DLBCL; n = 3) at another site, and 6 (12%) had prior FL (5) or DLBCL (1). Composite lymphomas associated with FLIS included 2 chronic lymphocytic leukemia/small lymphocytic lymphomas, 1 nodal marginal zone B-cell lymphoma, and 1 interfollicular classical Hodgkin lymphoma.
|Total #||# with progression to FL/DLBCL vs. total with follow-up (time)*||Histologic score, time to progression**|
|FLIS (27)||1/20 (5%; 3-118 mo, ave. 50.3 mo)||1A; 29 mo (FL)|
|FLIS composite (4)||1/4 (25%; 18-108, ave. 48.8 mo)||1A; 48 mo (DLBCL)|
|PFL (52)||5/16 (31%; 6-72 mo, ave. 31.9 mo)||3B; 72 mo (FL)|
|3A; 13 mo (FL)|
|1A; 45 mo (FL)|
|3B; 6 mo (FL)|
|1A; 32 mo (DLBCL)|