リンパ腫におけるwhole slide imaging診断の妥当性の検証

概要

Introduction
Whole slide imaging, also known as virtual microscopy, is the transformation of glass slides of the tissue section to digital images by WSI scanners which are run with a computer workstations and specific software. WSI has various pragmatic uses such as for diagnosis, education, research, and telepathology consultation.

Recently several reports have indicated that WSI can be used for routine pathological diagnosis. The College of American Pathologists (CAP) proposed in May 2013 13 graft guidelines for conducting validation studies of WSI for clinical use as well as use with digital pathology devices for primary diagnosis. However, many of them used only a small number of specimens alone and cases requiring immunohistochemistry or special staining, such as lymphoma cases were excluded from the studies. WSI validation studies for lymphoma have not been yet published and more studies are required prove the clinical values of WSI for pathological diagnosis. In this study, we assessed the usefulness of WSI in comparison with that of light microscopy (LM) for the diagnosis of lymphoma.

Materials and methods
For this study, 240 biopsies and resections of serial cases were retrieved from a study set of lymphoid lesions. All original diagnoses had been established by one of the authors who is a well-experienced pathologist based on the routine microscopic examinations, at least a half year before this study. More than half of the cases were nodal lesions (54.59%), while extra- nodal lesions consisted of those of the gastrointestinal tract (19.59%), skin (3.75%), and others.

All slides of H&E, immunohistochemical, and special staining were scanned using Nanozoomer 2.0 RS at 20x magnification properly according to CAP guidelines. The scanned images were stored in a mass storage environment.

The original- and the WSI-based diagnoses were compared for each case and the degree of agreement was determined by discussions with all evaluators. The results thus obtained were categorized into three classes: 1) concordance, defined as complete agreement between the two diagnoses; 2) minor discrepancy, slightly different without any clinical or prognostics significances; 3) major discrepancy, different interpretations with significant clinical implications.

Results and Discussion
Diagnostic agreement between WSI and microscopic diagnoses
The overall extent of agreement between WSI and microscopic diagnoses is calculated. Of 240 cases examined, the diagnosis was concordant for 223 cases (92.92%; 95% confidence interval, 88.90-95.82). Minor discrepancy was detected in fifteen cases, while major discrepancy was identified in the remaining two cases.

Similarly, the concordant rate was calculated for individual diagnostic categories and the most common diagnosis was diffuse large B cell lymphoma (96/240 cases, 40.0%), followed by follicular lymphoma (41 cases, 17.08%), non-specific reactive lymphadenopathy (13 cases, 5.41%) and others.

Review of the discrepant cases
One case with major discrepancy was an inguinal lymph node biopsy. The original light microscopic diagnosis was nodular lymphocyte predominant Hodgkin lymphoma, while evaluation with WSI, resulted in a diagnosis of peripheral T-cell lymphoma, NOS. On WSI, it was difficult to determine whether these T-cells were neoplastic, resulting in a final determination as neoplastic but without confidence. In addition, lymphocyte predominant (LP) cells were little less striking on WSI than on LM, so that the evaluator could not detect the cells. Histology review of this case confirmed that the original diagnosis was more appropriate than WSI diagnosis.

Another case with major discrepancy was a cervical lymph node biopsy from a right cervical lymphadenopathy. The original light microscopic diagnosis was tuberculosis with atypical B- cells infiltrate. In this case, large foci of caseous necrosis were found surrounded by epithelioid cells with Langerhans’s giant cells. Background lymphocytes were small and uniform with bland-looking morphology, but showed diffuse positivity for CD20. The reason for the original microscopic diagnosis was the presence of a few acid-fast bacilli on Ziehl-Neelsen staining, but these were not detected by WSI at x20 scanning magnification. In contrast, WSI diagnosis was low grade B-cell lymphoma, NOS with granulomatous reaction with undetermined significance. After the histology review, a final diagnosis of tuberculosis with coexisting low- grade B-cell lymphoma, NOS was made.

Of the fifteen cases with minor discrepancies, eleven were related to grading of follicular lymphoma. Eight of these cases were diagnosed as grade 2 on WSI, while the original diagnosis was grade 1. Another two cases, originally rated as grade 3a, was diagnosed as grade 2 on WSI and the last one was diagnosed as diffuse large B-cell lymphoma on WSI, while the original LM diagnosis was follicular lymphoma grade 3b. However, grading of follicular lymphoma and differentiating between diffuse large B-cell lymphoma and follicular lymphoma, grade 3b are considered to be fairly subjective, and inter- and intra-observer variations are common even for microscopic examinations, not from image quality of WSI, and do not affect the selection of therapies and are therefore not a significant problem. These differences of the remaining four case with minor discrepancies were considered to be the result of human factors, and not of image quality. One of these cases with an original diagnosis of high-grade B-cell lymphoma, NOS was diagnosed as diffuse large B-cell lymphoma on WSI. The lymphoma was composed of medium to large B-cells with an unusual immunophenotype, partial cyclin D1-positive, CD23 strongly positive, CD5-positive (weak), and a very high MIB1 index. Although pleomorphic variant of mantle cell lymphoma or high-grade transformation of chronic lymphocytic leukemia/small lymphocytic lymphoma were suspected, no specific diagnostic name could not be assigned also due to the small size of the specimen and absence of previous history of lymphoma. Another of these four cases, originally diagnosed as “atypical lymphoid cell infiltration (indeterminate for malignancy)” was diagnosed on WSI as “probable T-cell rich B-cell lymphoma”. The discrepancies in both diagnoses were in conclusive, rated as in the area of “borderline”, and categorized as minor. In one case of classical Hodgkin lymphoma, NOS was diagnosed as nodular sclerosis Hodgkin lymphoma on WSI; in the last case, nodular lymphocyte predominant Hodgkin lymphoma with a T-cell rich B-cell lymphoma-like area was diagnosed as simply T-cell rich B-cell lymphoma on WSI. Generally, the distinction between nodular lymphocyte predominant Hodgkin lymphoma and T-cell rich B-cell lymphoma is sometimes not very clear, so that this case was also classified as a minor discrepancy.

Conclusion
The findings of our study show high concordance and lower discordance rates for WSI and LM evaluations, and suggest that WSI can be used as an effective diagnostic tool for primary diagnosis of lymphoma cases. However, we found WSI image quality was still insufficient for evaluating detailed cellular morphology, especially in making a distinction on whether T-cell were neoplastic or not. We recommend to changing over to LM if there is a lack of confidence in reaching a diagnosis or if diagnosing a lymphoma proves to be difficult, and if necessary, that molecular testing should be used in conjunction with conventional LM lymphoma diagnosis.