Originally published as JHC exPRESS on June 23, 2008. doi:10.1369/jhc.2008.951087
Volume 56 (10): 893-900, 2008 Copyright ©The Histochemical Society, Inc. Role of Immunohistochemistry in Staging Diffuse Large B-cell Lymphoma (DLBCL)
Department of Haematology (DT), Australian National University Medical School (DT,JED,BS), Department of Anatomical Pathology (JED,AB), and Department of Epidemiology (BS), The Canberra Hospital, Canberra, Australia, and National Capital Private Hospital, Canberra, Australia (AM) Correspondence to: D. Talaulikar, MBBS, FRACP, FRCPA, GradCertHE, Department of Haematology, The Canberra Hospital, PO Box 11, Woden, ACT 2606, Australia. E-mail: dipti.talaulikar{at}act.gov.au
The use of immunohistochemistry (IHC) in staging bone marrow in non-Hodgkin's lymphoma (NHL) is largely limited to ambiguous cases, particularly those with lymphoid aggregates. Its role in routine clinical practice remains unestablished. This study aimed to determine whether the routine use of IHC in diffuse large B-cell lymphoma (DLBCL) would improve the detection of lymphomatous involvement in the bone marrow. It also sought to determine the impact of IHC on predicting survival compared with routine histological diagnosis using hematoxylin and eosin (H&E), Giemsa, and reticulin staining. The bone marrow trephines of 156 histologically proven DLBCL cases were assessed on routine histology, and IHC using two T-cell markers (CD45RO and CD3), two B-cell markers (CD20 and CD79a), and and light chains. IHC detected lymphomatous involvement on an additional 11% cases compared with histology alone. Although both routine histology and IHC were good predictors of survival, IHC was better at predicting survival on stepwise multivariate Cox regression analysis. IHC performed routinely on bone marrow trephines has the ability to improve detection of occult lymphoma in experienced hands. Furthermore, it is a better predictor of survival compared with routine histological examination alone. (J Histochem Cytochem 56:893–900, 2008)
Key Words: immunohistochemistry histology staging bone marrow trephine biopsy diffuse large B-cell lymphoma International Prognostic Index
IMMUNOHISTOCHEMISTRY (IHC) is a very valuable tool that, in the last three decades, has revolutionalized the practice of diagnostic histopathology. It is widely used to improve characterization of a number of tumors and to detect occult metastases, especially in lymph nodes. Applications in lymphoma mainly relate to providing information on the classification and subclassification of lymphomas in diagnostic primary tissue. Other applications include determining biological factors of prognostic significance (Lossos and Morgensztern 2006
Reported rates of BM involvement in NHL differ based on the subtype of NHL, with low-grade lymphomas having much higher rates of involvement (Harris et al. 1999
The implications of BM involvement also vary depending on the grade of lymphoma. Marrow involvement in DLBCL has implications for prognosis; lymphomatous infiltration in the marrow has been reported to correlate with poor survival (Yan et al. 1995
The role of IHC in staging BM has been upstaged, to some extent, by immunophenotyping by flow cytometry of BM aspirates. This is perhaps because the results obtained with flow cytometry are quantitative and perceived to be less prone to the errors that may be associated with a more subjective diagnostic tool such as IHC, particularly in inexperienced hands. The ready availability of flow cytometric analysis in most laboratories has also led to its widespread use. Indeed, there is recent evidence that flow cytometry plays an important role in staging of DLBCL and has an impact on outcome factors (Talaulikar et al. 2008
It is well known that BM involvement in NHL is more often apparent on trephine biopsy specimens rather than BM aspirates (Juneja et al. 1990
Most studies have focused on the use of IHC on BM trephines in ambiguous cases to differentiate between benign lymphoid aggregates and malignant infiltration. We are aware that many centers within and outside Australia do not use IHC routinely in staging bone marrows, partly because of the cost involved and partly because of the lack of evidence regarding its use. Other studies have looked at the use of IHC alone but have not reported results for routine morphology and immunostaining separately (Palacio et al. 2001 The role of IHC in routine clinical practice to detect occult lymphoma in the BM and its effect on patient survival is largely unknown. This study aimed to assess the clinical use of routine IHC analysis in staging bone marrows in DLBCL, including its effect on outcome factors such as survival.
Patients One hundred fifty-six retrospective cases diagnosed with histologically proven DLBCL at The Canberra Hospital from 1986 to 2005, on whom staging BM biopsies had been performed, were identified for the purpose of the study. After approval was obtained from the Australian Capital Territory (ACT) Human Research Ethics Committee, clinical information on patients was collected from the Medical Records department at The Canberra Hospital. The average age of the patient cohort (known in 154 cases) was 61 years (range, 20–87 years), and the male to female ratio was 1.5:1. Staging data were available in 148 patients. Using routine staging procedures, 37/148 (25%) had Stage I disease; 35/148 (23.6%) had Stage II disease; 45/148 (30.4%) had Stage III disease; and 31/148 (20.9%) had Stage IV disease. Baseline assessment of IPI was possible in 148 patients. Fourteen patients had an IPI of 0 (9.5%), 23 patients had an IPI of 1 (15.5%), and 36 had an IPI of 2 (24.3%). IPIs of 3, 4, and 5 were noted in 46 (31.1%), 22 (14.9%), and 7 patients (4.7%), respectively. The mean baseline IPI of the patient cohort was 2.41 with an SD of 1.3. Treatment data were available on 142 patients, with almost all patients having been treated with anthracycline-based regimens. Nine patients were treated with palliative intent with steroids alone or in combination with non–anthracycline-based drugs. Only 36 patients (22.2%) received rituximab. The median overall survival of the entire patient group was 58 months [95% confidence interval (CI), 33; 82 months].
BM Histology
All slides were reviewed blindly by two hematologists, with discrepant cases (n=20) being reviewed by a third. Cheson criteria were used to classify trephine biopsy samples as positive, negative, or indeterminate (Cheson et al. 1999
IHC The features described to define abnormality on IHC reflected the Cheson criteria for routine histology, although a fairly conservative approach was adopted by the pathologists to avoid false positives. Overall, location of infiltrates, size of cells, number of cells compared with controls, and nuclear morphology were used.
The presence of clusters of B cells was classified as abnormal or malignant when there were large number of clusters, the clusters were large sized, or they contained disproportionate numbers of larger cells. Scattered malignant cells may be missed quite easily on routine histology (Fraga et al. 1995
Statistical Analysis
Histology Of the 156 cases on which BMs could be evaluated, 24 were noted to be positive on routine histology; 6 cases were reported as indeterminate using Cheson criteria. Rather than using immunostaining to aid diagnosis, an attempt was made to resolve these on consensual review of routine H&E slides; all cases were agreed on as being positive for involvement on consensual review. H&E stains showed no evidence of involvement in 126 cases.
IHC The IHC findings for individual antibodies are listed in Table 1 . Eleven (25.6%) of the 43 involved cases had small cells, whereas the remaining 32 (74.4%) had large cells. Fourteen (32.6%), 10 (23.3%), and 19 cases (44.2%) had <1%, 1–5%, and >5% of B cells infiltrating the marrow, whereas T-cell infiltration was as follows: 32 (74.4%) cases with <1%, 4 (9.3%) cases with 1–5%, and 7 (16.3%) cases with >5% infiltration. Of all cases reported as positive on B-cell markers, only 15 showed clear evidence of light chain restriction. Twenty-three cases showed no light chain restriction.
Effect on Outcome IPI The results of IHC were added to those of routine histology to redefine BM involvement. A new revised IPI (rIPI) was computed for all cases based on the IHC results. Changes to the IPI essentially occurred when stage of disease was upgraded from Stage 1 or 2 to Stage 4 disease. Marrow involvement was also calculated as an additional extranodal site of involvement, further changing the IPI in some cases. Of 144 cases where rIPI was assessable, 9 cases had an rIPI of 0, 18 had an rIPI of 1, and 33 had an rIPI of 2. Forty, 31, and 13 cases had an rIPI of 3, 4, and 5, respectively.
Survival
Kaplan-Meier curves were created to assess the impact of small cell vs large cell infiltration, and the degree of B-cell infiltration. The median survival times for cases with discordant (small cell) involvement were better than those for concordant or large cell involvement (33 and 22 months), although the difference was not significantly significant (p=0.7). The median survival of cases with <1%, 1–5%, and >5% B-cell infiltration was 40, 33, and 15 months. In other words, prognosis seemed to worsen with increased B-cell infiltration, although this again was not statistically significant (p=0.7).
Multivariate Analysis
To study the effect of treatment with rituximab on survival, this too was considered, but not found to contribute significantly to the Cox regression model (p=0.8). However, when a similar Cox regression analysis was performed to compare revised and baseline IPI, rIPI did not contribute significantly to survival over and above baseline IPI (p=0.4). Although the mean rIPI among patients who did not survive was higher than the mean baseline IPI [3.22 (95% CI, 2.87, 3.57) vs 2.92 (95% CI, 2.59, 3.25)], this was also the case in patients who were alive at the time of analysis [2.38 (95% CI, 2.01, 2.63) vs 2.03 (95% CI, 1.73, 2.32)].
This study looked at the role of routine IHC in staging DLBCL at initial diagnosis. Our results indicate that, in experienced hands, use of immunostaining surpasses routine histology by detecting occult disease in 10% of cases. Moreover, immunostaining alone is a stronger predictor of survival than routine histology.
Detection of occult BM involvement by lymphoma hinges on the adequacy of both routine histological diagnosis and IHC analysis. There are several variables that affect adequacy of routine histological diagnosis on BMs. It was previously believed that bilateral trephine biopsies increased the yield from staging BMs in NHL (Juneja et al. 1990
The mean number of levels examined on H&E sections was 3.7 (range, 1–8). Fifty cases had less than four levels examined; of these, 12 had three levels examined, 37 had two levels examined, and only one had a single level examined. Including a single level each on Giemsa stain and silver reticulin stain, only one case had less than four levels. It is possible that some of the positive results on immunostaining seen in our study were related to examination of more tissue. Two examples where discrete populations of large B cells were noted on immunostaining that were not apparent on careful review of routine histology slides are shown in Figure 3
. A previous study by Campbell et al. (2003)
It is acknowledged that the detection of lymphoma in the marrow is subjective and depends on the experience and skill of the observers, particularly in interpretation of lymphoid aggregates as being benign or malignant. The use of standardized criteria is now therefore recommended for classifying cases as positive, negative, or indeterminate for involvement with lymphoma (Cheson et al. 1999
There are other differences between our study and that of Hanson et al. (1999)
Adequacy of IHC analysis is a contentious issue prone to the same subjective errors as routine histology. We used two B-cell and two T-cell markers to corroborate our findings. CD20 and CD3 have been shown to be most sensitive at assigning lineage in diffuse aggressive NHL (Chadburn and Knowles 1994
We found in our series of patients that, of the 43 cases detected to have involvement on IHC, 11 (25.6%) had small cells, whereas the majority (32, 74.4%) had large cells. This is a higher degree of concordant involvement than has been reported by Chung et al. (2007)
A few studies have addressed the issue of detection of histologically inapparent disease using immunostaining. Fraga et al. (1995)
Some technical issues were also highlighted by the study and deserve comment. Variable expression was noted on the two B-cell markers CD20 and CD79a. Previous studies have reported that decalcification, particularly with 5% nitric acid, has negative effects of certain clones of CD20, CD79a, CD5, and CD43 (Miller et al. 2000
We were able to establish clonality in only one third of cases (15/42, 35.7%). There is some literature to suggest that flow cytometry may show variable expression of antigens from different anatomic sites in cases of NHL (Gervasi et al. 2004 There are a number of advantages to use of routine immunostaining of trephine biopsies for staging DLBCL. IHC techniques are generally well established, available in most centers, and relatively cost effective. They enable the examination of a greater number of levels of the biopsy in a more comprehensive and sensitive manner and are useful in the detection of additional clusters of malignant cells and that of scattered malignant cells among normal hemopoietic cells.
Despite the use of more realistic measures of routine histological diagnosis such as unilateral biopsies and assessment of less than optimal trephine lengths, we have been able to show that immunostaining in experienced hands is more effective at predicting survival than routine histology. There are several other limitations of this study besides those inherent to retrospective data. We acknowledge that results of IHC analysis are subjective and can be very variable in less experienced hands. Also, there may be a degree of variability caused by the use of different antigen retrieval methods and processing of specimens (Miller et al. 2000
In summary, we showed that IHC analysis using B- and T-cell markers detects morphologically inapparent marrow involvement in
The authors acknowledge the financial support provided for the study by the Private Practice Trust Fund, The Canberra Hospital, and the equipment grant provided by The Leukaemia Foundation, Australia. The principal investigator/author received a supplementary scholarship from the Arrow Bone Marrow Transplant Foundation, New South Wales, for the project.
Received for publication February 11, 2008; accepted June 11, 2008
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