For antibody primary screening using paraffin-embedded tissue microarrays, how should spot diameter and replicate spots be selected?

For antibody initial screening, do not overemphasize the number of cores; what matters most is case representativeness and scoring consistency. If tumor heterogeneity is relatively high, such as in hepatocellular carcinoma and breast cancer, it is recommended to use 3 replicate cores per case; if heterogeneity is low, 2 cores are generally sufficient to handle occasional missing cores. For statistical analysis, it is recommended to integrate several cores from one case into a single grade or H-score, and not simply treat the cores as independent samples, otherwise the sample size will be exaggerated. 1.0 mm is suitable for initial screening of large sample sets, while 1.5 mm is suitable for initial screening of moderate sample sizes or samples with relatively high heterogeneity; since you process 20 slides at a time, 1.5 mm is more appropriate. Before constructing the TMA, first optimize antibody dilution and retrieval conditions using regular FFPE slides, which can save a considerable number of TMA sections.

I suggest asking the supplier to provide an HE scan or dot map of the TMA to first check the dot integrity rate, so that missing dots are not discovered only after staining. A dot diameter of 1.5 mm with 2 replicate dots per case is a reasonable compromise, keeping both the number of sections and the cost manageable. Embedding depth generally does not need special specification; proper preparation ensures the tissue core is long enough, and cutting 20 consecutive sections is usually not a problem. I am more concerned about whether positively charged slides are used and whether baking is sufficient. If individual dots are lost later, keep unstained blank sections and immediately redo them; do not attribute all causes to small dots. You can also cut 10 sections for trial staining first, then decide based on the results whether to cut more or continue.

For initial screening, I recommend using 1.5 mm spots. Although 1.0 mm spots allow more cases per slide, they have a higher edge proportion and are more prone to lifting during sectioning and antigen retrieval; when tumor heterogeneity is pronounced, small spots are also more likely to produce false negatives. Since you stain 20 slides at a time, tissue volume is not the bottleneck, and 1.5 mm spots allow more comfortable microscopic interpretation. Use at least 2 replicate spots per case. If the main focus is comparing tumor versus normal, use 2-3 spots for the tumor area and 1-2 spots for the normal area; for statistical analysis, use the number of cases as the sample size, and take consistent or averaged values from replicate spots, not treating each spot as an independent n. For initial screening, 2 spots are generally sufficient; for subsequent semiquantitative work, consider 3 spots.

Section loss is more related to sectioning, baking, and retrieval conditions and cannot be solved by embedding depth alone. For conventional recipient wax blocks, the punch depth is 2-3 mm, and the tissue core should be flush or slightly protruding. After trimming to the largest section plane, continuous sectioning can be performed. If there is concern, the manufacturer can trim until the tissue is fully exposed and then leave an additional 30-50 μm. A section thickness of 4 μm is recommended, baking at 60-65°C for more than 2 hours, and baking for another 10 minutes before retrieval. A 1.0 mm spot is indeed more prone than a 1.5 mm spot to edge detachment during high-pressure retrieval, so using 1.5 mm for initial screening is more reliable. If 1.0 mm must be used, it is recommended to switch to positively charged adhesive slides and control the retrieval temperature at around 95°C to avoid vigorous boiling.