[1398] Discordance of Ki-67 Expression between Primary Site and Bone Marrow in Patients with B-Cell Non-Hodgkin Lymphomas

Juanita Evans, Michael Bayerl, Malcolm Acon-Laws, Jozef Malysz. Penn State Milton S Hershey Medical Center, Hershey, PA

Background: Previous studies have shown that an increased Ki-67 proliferation index (PI) in B-cell non-Hodgkin lymphomas (BNHL) is associated with aggressive disease. Bone marrow (BM) biopsies are performed for diagnosis/staging in patients with BNHL. We hypothesize that the PI of a lymphoma present in the BM does not always correlate with the PI in its extramedullary location.
Design: Tissue specimens from patients with primary site and BM involvement by BNHL were identified. Dual IHC staining for Ki-67 (AEC chromogen) and CD20 (DAB chromogen) was performed. PI for each site was determined by using Ki-67 expression in 100 lymphoma cells in a representative section. Clinical data including demographics, sites of involvement, IPI, and survival were collected. T-test with significance set at a p<0.05 was used for comparisons.
Results: Ample tissue at both sites of involvement was present in 27 patients. 3 morphologic groups were observed: Large cell lymphoma (LCL) at the primary site with large cells in the BM (LCL-L), LCL at the primary site with discordant small cells in the BM (LCL-S), and small cell lymphoma at the primary site with small cells in the BM (SCL-S). Please refer to the table for results.

Mean PI at primary versus BM sites of BNHL
Group# of CasesPrimary site mean PIBM site mean PIp-value
All Cases2715.43.40.003
ALL LCL1226.660.006
ALL SCL-S154.31.30.019

As expected, all LCLs had a higher mean PI at the primary site as compared to all SCLs (26.6% vs 4.3%, p = 0.001). The overall mean PI of the primary site was greater than the BM site. For all morphologic subdivisions, the primary site had a higher mean PI than the BM. This was only statistically significant for LCL-S (p = 0.011) and SCL-S (p = 0.019). The mean PI at the primary site of all cases was higher in patients with a survival ≤12 months than those with survival >12 months (25.3% vs 10.5%, p = 0.034). No difference was noted in the mean PI at the BM in patients stratified by survival (7.2% vs 1.4%, p = 0.084).
Conclusions: In patients with primary site and BM BNHL, the PI was higher in the primary site than the BM. When grouped by morphology, the SCL-S and LCL-S showed a statistically significant difference in mean PI of primary compared to BM sites, whereas the LCL-L did not. Higher PI in the primary site was associated with survival; whereas PI in the bone marrow was not. This suggests that Ki-67 expression of a BNHL in the BM should not be used as a surrogate prognostic indicator of PI of the lymphoma in its extramedullary site.
Category: Hematopathology

Tuesday, March 20, 2012 1:00 PM

Poster Session IV # 214, Tuesday Afternoon


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