The slide to be stained for Ep-CAM comprised:

1. Appendix, 2. Kidney, 3. Adrenal gland, 4. Lung carcinoid, 5 & 6. Renal clear cell carcinoma.

All tissues were fixed in 10% neutral buffered formalin.

Criteria for assessing an Ep-CAM staining as optimal included:

• A strong, distinct, predominantly membranous staining of virtually all the columnar epithelial cells of the appendix.
• A moderate to strong predominantly membranous staining of the epithelial cells of the renal collecting tubules, and an at least weak basolateral staining of the epithelial cells of the proximal tubules of the kidney.
• A moderate to strong, distinct, predominantly membranous staining of virtually all the neoplastic cells of the lung carcinoid.
• An at least weak predominantly membranous staining of scattered neoplastic cells in the two renal cell carcinomas.

145 laboratories participated in this assessment. 4 laboratories used an inappropriate Ab. Out of the remaining 141 labs 45 % achieved a sufficient mark. In table 1 the antibodies (Abs) used and marks are summarized.

Table 1. Abs and assessment marks for EpCAM, run 32

1) Proportion of sufficient stains (optimal or good), 2) Proportion of sufficient stains with optimal protocol settings only, see below.

Following central protocol parameters were used to obtain an optimal staining:

Concentrated Abs
mAb clone Ber-EP4: The protocols giving an optimal result were all based on heat induced epitope retrieval (HIER) using either Target Retrieval Solution (TRS) low pH 6.1 (Dako) (8/21)* or Diva Decloaker pH 6.2 (Biocare) (2/2) as the retrieval buffer. The mAb was typically diluted in the range of 1:50-1:400 depending on the total sensitivity of the protocol employed. Using these protocol settings 18 out of 22 (82 %) laboratories produced a sufficient staining (optimal or good).
*(number of optimal results/number of laboratories using this buffer)

mAb clone MOC-31: The protocols giving an optimal result were all based on HIER using either TRS high pH 9 (3-in-1) (Dako) (1/1), TRS high pH 9 (Dako) (1/1), TRS low pH 6.1 (Dako) (1/2) or EDTA/EGTA pH 8 (1/1) as the retrieval buffer. The mAb was typically diluted in the range of 1:20-1:50 depending on the total sensitivity of the protocol employed. Using these protocol settings 8 out of 8 (100 %) laboratories produced a sufficient staining.

mAb clone VU-1D9: The protocols giving an optimal result were all based on HIER using Cell Conditioning 1  (BenchMark, Ventana (1/3)) or Citrate pH 6 (1/1) as the retrieval buffer. The mAb was typically diluted in the range of 1:20-1:100 depending on the total sensitivity of the protocol employed. Using these protocol settings 3 out of 4 (75 %) laboratories produced a sufficient staining.

Ready-To-Use Abs
mAb clone Ber-EP4 (prod. no. IS/IR637, Dako): The protocol giving an optimal result was based on HIER in PT-Link using TRS low pH 6.1 and an incubation time of 20 min. in the primary Ab and EnVision Flex (K8000) as the detection system. Using these protocol settings 12 out of 13 (92 %) laboratories produced a sufficient staining (optimal or good).

mAb clone MOC-31 (prod. no. PM403, Biocare): The protocol giving an optimal result was based on proteolytic pre-treatment using Pepsin 20 for min. at room temperature, an incubation time of 45 min. in the primary Ab and MACH4 (4U534) as the detection system

The most frequent causes of insufficient stains were:

- Inappropriate HIER buffer (an alkaline buffer for the mAb clone Ber-EP4)
- Less successful performance of the mAb clone Ber-EP4 on the BenchMark, Ventana  platform.
- Proteolytic pre-treatment
- Too low concentration of the primary Ab
- Use of low sensitive detection systems

In this assessment and in concordance to the previous NordiQC assessments, virtually all laboratories were able to demonstrate Ep-CAM in the columnar epithelial cells of the appendix, whereas the prevalent feature of the insufficient staining results was a too weak or false negative staining of the neoplastic cells of the lung carcinoid and in particular of the two renal cell carcinomas. For the most widely used mAb clone Ber-EP4 the proportion of sufficient results was highly influenced by the pre-treatment applied and the IHC platform used. First of all the pass rate was significantly lower if proteolytic pre-treatment was used compared to HIER. If proteolytic pre-treatment was used 10 out of 36 protocols (28 %) were assessed as sufficient and none of these were optimal. If HIER was applied, 42 out of 75 protocols (56 %) were assessed as sufficient, out of which 11 (15 %) were optimal. A significant difference in the overall performance for the mAb clone Ber-EP4 was also related to the HIER buffer and thus the IHC platform applied. If HIER was based on TRS low pH 6.1 (Dako) and subsequently IHC was performed by an open IHC platform such as the Autostainer (Dako or LabVision) 28 out of 33 laboratories (85 %) produced a sufficient staining, out of which 11 (33 %) were optimal. Using the fully automated platform BenchMark XT or BenchMark Ultra, Ventana, and HIER based on Cell Conditioning 1, pH 8.5, 19 out of 19 protocols were assessed as insufficient.

As an alternative to TRS low pH 6.1, Dako, it was observed that HIER based on DIVA decloaker solution pH 6.2 , Biocare gave an optimal staining result in 2 out of 2 protocols for the mAb clone Ber-EP4.

The most successful and robust assay for Ep-CAM based on the mAb clone Ber-EP4 in this assessment was obtained by the Ready-To-Use (RTU) system from Dako giving a pass rate of 93 % (13 out of 14 laboratories)out of which 11 % (1 laboratory) were assessed as optimal. In comparison the RTU system from Ventana based on the same mAb gave a pass rate of 13 % (1 out of 8 laboratories) and none were assessed as optimal.

The mAb clone MOC31 and VU-1D9 gave a slightly different staining pattern in both the normal kidney and in the two renal clear cell carcinomas. In the kidney the epithelial cells of the collecting tubules showed a moderate to strong membranous staining similar to the pattern seen for the mAb clone Ber-EP4, but also an increased staining in the basolateral membranes of the epithelial cells of the proximal tubules. The mAb clone MOC31 and VU-1D9 also typically labelled a higher proportion of the neoplastic cells in the two renal cell carcinomas. For the mAb MOC31 an optimal staining typically was obtained by HIER in e.g. TRS low pH 6.1 (Dako), but an optimal result could also be obtained by other HIER buffers with an alkaline pH as EDTA pH 8 and TRS High pH 9 (Dako) and by the use of proteolytic pre-treatment.
The mAb clone VU-1D9 was the only marker for Ep-CAM giving an optimal staining result on both an open IHC platform, Autostainer (LabVision), using HIER in Citrate pH 6 and a fully automated platform, BenchMark Ultra (Ventana), using HIER in Cell Conditioning 1.

Kidney was the most reliable positive control for Ep-CAM. A moderate to strong membranous staining must be seen in the epithelial cells of the collecting ducts, whereas optimally an at least weak basolateral membranous staining should be seen in the epithelial cells of the proximal tubules. Appendix can not be recommended as the columnar epithelial cells have a high expression of EP-CAM and thus will not identify a protocol with a too low sensitivity.

This was the 3rd NordiQC assessment of Ep-CAM (see table 3). A significant decrease in the proportion of sufficient results was seen in this run compared to the previous runs. This is most likely related to a combination of more challenging material circulated and many new laboratories participating for the first time. For the laboratories participating for the first time the pass rate was 37 % (25 out of 67), whereas the pass rate was 51 % (38 out of 74 laboratories) for the laboratories participating in previous runs.
 

Table 2: Proportion of sufficient results for EpCAM in the four NordiQC runs performed

Conclusion
The mAb clones Ber-EP4, MOC31 and VU-1D9 can all be used for the demonstration of Ep-CAM. HIER in TRS low pH 6.1 (Dako) or Diva Decloaker pH 6.2 (Biocare) seems mandatory for an optimal performance of the mAb clone Ber-EP4. For the mAb clones MOC31 and VU-1D5, HIER in either an alkaline buffer or a non-alkaline buffer such as Citrate pH 6 could be used to obtain an optimal performance. Kidney is a recommendable positive control: A moderate to strong membranous staining must be seen in the epithelial cells of the renal collecting tubules while an at least weak membranous staining should be seen in the epithelial cells of the proximal tubules.