You may use consecutive sections of the same block and have the tissue evaluated by an experienced pathologist to obtain the histology and select the areas for special transcriptomics. But you need to be aware that using a consecutive section might introduce issues due to section-to-section variability requiring proper integration if you aim for single cell analysis of morphology and transcriptome.

I agree with Sabine, staining with H&E and evaluating one tissue section before and one after the one you are interested in (for spatial biology applications) should do the trick. A skilled pathologist can mark the areas of interest for you. Areas that have plenty of tumor cells and minimum normal or necrotic tissue should be the desired options.

Another option is obtaining cores from your FFPE blocks that possess the desired characteristics and re-embedding them, which again requires the services of a skilled pathologist that will mark these areas. This however is somewhat time consuming but it would provide you with adequate material for many experiments in the future. The technique is called tissue microarray and you can evaluate tissues from several different donor FFPE blocks on the same slide in one go (minimizing your staining costs).

To ensure you capture regions of tumor cells in spatial transcriptomics tissue research, carefully select tissue sections with visible tumor areas based on H&E staining, use high-resolution imaging to precisely target tumor regions when placing the tissue on the spatial transcriptomics platform, and consider employing computational analysis methods to identify and enrich for tumor-specific gene expression patterns within the captured spatial data; this includes pre-experiment planning to identify appropriate tumor markers and optimizing tissue sectioning and placement on the capture platform to maximize the sampling of tumor regions.