FFPE tissue blocks are samples of various human tissues archived for future use by clinical pathologists. Immunohistochemistry (IHC) is performed on the sample tissues, and the results provide information which is vital for projects on diseases such as cancer. Tissue microarray (TMA) is a more recent technique which allows detailed analyses of more than one specimen simultaneously.
The process of the FFPE tissue array begins when the tissue blocks which are to be included in the array are selected. A section from each of the blocks is then exposed to hematoxylin and eosin stain to determine the region which contains the information which is required. The area of interest is circled and used as a guide to the identify the part of the FFPE donor tissue where the required information is contained. Once the core is obtained, it is mounted in a recipient paraffin block following a pre-determined arrangement.
It is advisable to obtain four cores from a single tissue block so as to acquire more information on the disease and various biomarkers.
Before the preparation of the microarray, a sector map which indicates the location of each core sample is designed. In most instances, this is done by a qualified pathologist or a histotechnologist. The size of the core is usually 0.6mm, but in some cases can be as large as 2mm.
Use of FFPE tissue microarray
Initially, TMAs were mostly used in cancer research, but the technology is increasingly being used in pathology and a variety of in situ analysis.
For a single cancer experiment to be carried out, samples of different types of tumors and from various people with varying disease progression are analyzed at the same time.
Benefits of the array
I. Small piece of the tissue block is required
This method makes it possible to use 5mm of FFPE tissue for a single molecular analysis. The result of this is better utilization and preservation of the original block of tissues as the number of archived blocks is much less than that required for various the clinical applications.
II. Time efficiency
Many samples can be analyzed at the same time. A lot of valuable information is collected in a single experiment which is preferable to studying the samples individually.
III. Uniform analysis
When using TMA, the tissues are given similar treatment and are studied under the same physical conditions. As a result, standard observations are recorded as the array eliminates technical and environmental differences.
V. Cost effective
The procedure uses fewer amounts of the reagents compared to if the tests are run individually. This reduces the cost of researching by a huge margin.
Nonetheless, there are limitations of tissue microarray, an example being when the various tissue samples required for the analysis are not available. Furthermore, the small size of tissue which is extracted may not be a fair representation of the entire profile of the affected tissue.
Though the facilities are expensive, TMA has proven to be an effective technique, especially in cancer research. With time, the technology is likely to be upgraded, and its digitalization would break ground in the field of biomedical research.