[1359] 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.

Clinical Outcome in FLIS and PFL
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)
* Excluding follow-up on patients with prior/synchronous FL/DLBCL, and/or treated with chemotherapy/radiation. **1 = < 5 follicles involved, 2 = 5-10 fol, 3 = > 10 fol; A = < 50% of follicles involved, B = > 50% fol.

Conclusions: While FLIS may represent an early step in follicular lymphomagenesis, PFL is more likely to reflect involvement by FL/DLBCL elsewhere and more likely to progress. FLIS has a more frequent association with composite lymphoma than would be expected by random chance (4 of 31 total, 13%).
Category: Hematopathology

Monday, March 22, 2010 1:00 PM

Poster Session II # 159, Monday Afternoon


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