Scoring of MYC protein expression in diffuse large B-cell lymphomas: concordance rate among hematopathologists

Abstract

Recent studies have shown that immunohistochemical evaluation of MYC protein expression in diffuse large B-cell lymphoma is a useful prognostic tool with high concordance rate among pathologists. Concordance in these studies was assessed among few pathologists from one institution by scoring tissue microarrays. In daily practice, MYC evaluation is performed on entire tumor sections by a diverse group of pathologists. In our study, nine hematopathologists from two institutions scored whole-tissue sections of two sets of cases. The training set included 13 cases of diffuse large B-cell lymphoma and 4 cases of Burkitt lymphoma. The validation set included 18 cases of diffuse large B-cell lymphoma and 1 case of Burkitt lymphoma. MYC positivity was defined as Z40% of tumor cells demonstrating nuclear staining similar to prior studies. The mean score for each case was used to determine MYC status with discrepant cases defined as having any score causing a different MYC status designation. Discrepant cases from the training set were characterized by staining heterogeneity, extensive necrosis or crush artifact and had mean scores within 15 percentage points of 40%. Cases from the validation set that demonstrated any of these features were scored twice on two different days. Overall concordance was moderate (Kappa score: 0.68, P-valueo0.001) with no significant change between the two sets (Kappa scores: 0.69 vs 0.67). Thirty-nine percent of cases were discrepant. The findings indicate that a significant number of diffuse large B-cell lymphomas are inherently difficult to score due to staining heterogeneity. The effect of heterogeneity can be under-represented when concordance is measured among few pathologists scoring tissue microarrays. Careful scoring strategy in our study failed to improve concordance. In the absence of specific instructions on how to deal with heterogeneity, caution is advised when evaluating MYC expression in diffuse large B-cell lymphoma.

Diagnosis of ‘double hit’ diffuse large B-cell lymphoma and B-cell lymphoma, unclassifiable, with features intermediate between DLBCL and Burkitt lymphoma: when and how, FISH versus IHC

“…18,19 However, the variably reported results in the literature suggest that staining varies between different laboratories and, in my experience, staining within even BL can vary based on cell viability and probably fixation-related issues. Problems with reproducibility in the use of the 40% cutoff have also been reported 53 and Horn et al did write in 2013 that: "paying tribute to the fact that only recent and as yet incomplete experience has been gained for immunohistochemical stainings with the anti-MYC antibody … at the moment we strongly advise the use of a combined MYC-FISH and IHC model." 5 Furthermore, even if perfect, MYC IHC could only be used as a screen for DHL because they also require BCL2 and/or BCL6-R and neither can be predicted based on BCL2 or BCL6 expression.…”

Approach to the diagnosis and treatment of high-grade B-cell lymphomas with MYC and BCL2 and/or BCL6 rearrangements

“…10 Factors affecting poor concordance between hematopathologists include crush artifact and variation in staining intensity and tumor content. 80 Furthermore, thresholds that categorize patients as being positive vary among studies and still require prospective validation. Although BCL2 expression is routinely assessed in pathology, MYC expression is not assessed in all laboratories.…”

Definition of MYC genetic heteroclonality in diffuse large B-cell lymphoma with 8q24 rearrangement and its impact on protein expression

“…A novel commercial monoclonal antibody has improved the detection of MYC protein expression, [6][7] however, immunohistochemistry assessment and quantification still remains difficult because of highly variable MYC expression. [11][12] In this regard, image digital analysis and computerized assisted interpretation may prove to be a valid aid. Applying this strategy (Aperio) to our series of 43 MYC rearranged diffuse large B-cell lymphoma, we observed high (440%, immunohistochemistry positive) and low (o 40%, immunohistochemistry negative) MYC protein expression in 88% and 12% cases, respectively, confirming previous observations.…”

“…Although the mechanisms responsible for the loss of MYC expression are still unclear, the presence of heteroclonality may explain the low MYC expression in 10-30% of diffuse large B-cell lymphoma with MYC rearrangement. 5,[8][9][10][11][12]26 Further studies using combined method of FISH and immunofluorescence (such as FICTION technique) may help to characterize more precisely the relationship between MYC gene and protein status in all these different clones.…”

“…[6][7] In contrast, in MYC rearranged diffuse large B-cell lymphoma, the association between rearrangement and protein expression is less clear, as approximately one-third of cases with this rearrangement show protein staining in o 40% of the tumor cells. 5,[8][9][10][11][12] Conventional and molecular cytogenetic studies of diffuse large B-cell lymphoma have described cases with MYC rearrangement that are characterized by complex karyotypes, revealing the presence of different populations of cells with loss/extra copies of derivatives of the MYC rearrangement and/or extra copies of chromosome 8. [13][14][15][16][17][18] The occurrence of these alterations and their contribution to protein expression remains unknown.…”