What are the Advantages?
Welcome to the Yale Cancer Center/Pathology Tissue Microarray Facility, a Cancer Center shared resource. We provide the university community with services related to tissue microarray technologies. Services are also available for the biotech and pharmaceutical industries.
There are numerous advantages to this technology including:
- Amplification of a scarce resource
- Experimental uniformity
- Decreased assay volume
- Does not destroy original block for diagnosis
A standard histologic section is about 3-5mm thick, with variation depending on the submitting pathologist or tech. After use for primary diagnosis, the sections can be cut 50-100 times depending on the care and skill of the sectioning technician. Thus, on average, each archived block might yield material for a maximum of 100 assays. If this same block is processed for optimal microarray construction it could routinely be needle biopsied 200-300 times or more depending on the size of the tumor in the original block (Theoretically it could be biopsied 1000's of times based on calculations of area, but empirically, 200-300 is selected as a conservative estimation) Then, once tissue microarrays are constructed, they can be judiciously sectioned in order to maximize the number of sections cut from an array. The sectioning process uses a tape-based sectioning aid (from Instrumedics Inc.) that allows cutting of thinner sections. Optimal sectioning of arrays is obtained with about 2-3 µm sections. Thus instead of 50-100 conventional sections or samples for analysis from one tissue biopsy, the microarray technique could produce material for 500,000 assays (assuming 250 biopsies per section times 2000 2.5 µm sections per 5mm array block) represented as 0.6 mm disks of tissue. Thus this technique essentially amplifies (up to 10,000 fold) the limited tissue resource.
Using this technology, each tissue sample is treated in an identical manner. Like conventional formalin-fixed paraffin embedded material, tissue microarrays are amenable to a wide range of techniques including histochemical stains, immunologic stains with either chromogenic or fluorescent visualization, in situ hybridization (including both mRNA ISH and FISH), and even tissue micro-dissection techniques. For each of these protocols, conventional sections can have substantial slide to slide variability associated with processing 300 slides (for example, 20 batches of 15 slides). The tissue microarrays allow the entire cohort to be analyzed in one batch on a single slide. Thus reagent concentrations are identical for each case, as are incubation times and temperatures, wash conditions, and antigen retrieval, if necessary.
Another significant advantage is that only a very small (a few µl) amount of reagent is required to analyze an entire cohort. This advantage raises the possibility of use of tissue microarrays in screening procedures (for example in hybridoma screening), a protocol that is impossible using conventional sections. It also saves money when reagents are costly.
Finally, there are occasions where the original block must be returned to the patient or donating institution. In these cases the block may be cored a few times without destroying the block. Then upon subsequent sectioning, it is still possible to make a diagnosis, even though tissue has been taken for array-based studies. This is illustrated in the adjoining figures.