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Assessment Run 6 2002
 

CD20

The slides to be stained for CD20 contained four small lymphocytic lymphomas/chronic lymphatic leukaemias (specimens 1-4), an atypical lymphoid proliferation (specimen 5), a colon carcinoma (specimen 6), three Hodgkin lymphomas LP (specimens 7-9),  three follicular lymphomas (specimens 10-12), and pieces of myometrial smooth muscle (SM).

62 laboratories submitted stainings. All used mAb L26 (DakoCytomation, Zymed og Ventana). All but one used HIER as pre-treatment.

At the assessment, 29 laboratories (47%) achieved optimal staining, 21 (34%) acceptable, 8 (13%) borderline, and 4 (6%) poor. The basis for an optimal result was an intense and distinct staining of cell membranes in cells expected to stain.

Mandatory for an optimal CD20 staining reaction was the use of an appropriately diluted Ab in combination with an efficient HIER protocol.

The most frequent reasons for an insufficient staining were:
- too dilute Ab (particularly when a less sensitive protocol was used, e.g., the use of AEC as the chromogen)
- insufficient HIER (too short heating time, particularly when citrate pH 6 was used)
- no pretreatment
A normal lymph node is appropriate for control. A continuous membranous staining should be seen in most B-cells.
Examples of good protocols

Fig. 1a. Optimal staining using mAb L26. Small lymphocytic lymphoma.

Fig. 1b. Optimal staining using mAb L26. Another small lymphocytic lymphoma.
Fig. 2a. Another optimal staining using mAb L26. Same field as in Fig.1a. Fig. 2b. Another optimal staining using mAb L26. Same field as in Fig. 1b.
Fig 3a. Acceptable staining using mAb L26. Same field as in Fig. 1a and 2a. Fig. 3b. Acceptable staining (close to borderline) using mAb L26. Same field as in Fig. 1b and 2b.
Fig 4a. Insufficient staining using mAb L26. Same field as in Fig. 1a, 2a and 3a. Apparently strong staining of the tumour, however, compare with Fig. 4b. Fig. 4b. Insufficient staining using mAb L26. Same field as in Fig. 1b, 2b and 3b.
Fig 5a. Insufficient staining using mAb L26. Same field as in Fig. 1a, 2a, 3a and 4a. Apparently strong staining of the tumour, however, compare with Fig. 5b. Fig. 5b. Insufficient staining using mAb L26. Smooth muscle cells are strongly false positive.
MV/SN/AS

Last update 16-06-2004