Quality Control and Standardization Construction of FFPE Tissue Microarrays

Quality Control Fundamentals for Tissue Fixation and Embedding

The quality of FFPE tissue microarrays first depends on the original tissue processing. Generally, neutral formalin fixation should be performed as soon as possible after tissue collection, with fixation time adjusted according to tissue volume and type, usually sufficient penetration being appropriate. Insufficient fixation may lead to antigen or nucleic acid degradation, while excessive fixation may cause antigen masking. During embedding, excessive dehydration or inadequate wax infiltration should be avoided to prevent fragmentation or curling during sectioning. Donor paraffin blocks must be reviewed by a pathologist before sampling to confirm that the target region is representative.

Key Control Points in Array Construction

Microarray construction typically uses an arrayer to punch tissue cores from donor paraffin blocks and transfer them to recipient paraffin blocks according to preset coordinates. At this stage, the tissue core diameter needs to be controlled, with common specifications including 0.6 mm, 1.0 mm, 1.5 mm, etc., and the specific choice depends on sample size and detection purpose. After construction, the array integrity can be observed under low magnification to remove displaced, missing, or deformed spots. Before re-embedding and sectioning, recipient paraffin blocks generally need moderate heating to fuse the tissue cores with the recipient wax to prevent detachment during sectioning.

Quality Control Measures for Sectioning and Staining

Section thickness is usually controlled at 3–5 μm to ensure tissue structure and antigen accessibility. Serial sections can be used for detection of different markers, but section order and storage conditions should be noted. Antigen retrieval is required before staining, commonly using heat-induced or enzymatic digestion methods, with specific conditions determined according to antibody instructions and preliminary experimental results. Each staining batch is recommended to include positive controls, negative controls, and blank controls to evaluate the stability of the staining system. During interpretation, the localization of positive signals should be clearly defined, such as cell membrane, cytoplasm, or nucleus, and multi-person blinded scoring or digital image analysis assistance should be used.

Data Recording and Reproducibility Assurance

Standardized recording is an important component of quality control. Generally, it is necessary to record the donor source, pathological diagnosis, sampling sites, microarray coordinates, antibody lot numbers, staining protocols, and image acquisition parameters. For multicenter studies, unified standard operating procedures and interpretation guidelines should also be established before the experiment begins, and consistency assessment should be conducted. If deviations in results occur between different batches, factors such as fixation, sectioning, retrieval, or antibody changes should be promptly investigated. A good quality control system helps improve the reliability and reproducibility of FFPE tissue microarray data and also provides a credible basis for subsequent biomarker evaluation.