The significance of this protocol over previous prostate sampling methods is that it gives us a higher confidence of targeting fresh tumor tissue for research. Therefore, we can take the fresh tissue straight back to the lab and use it for culture or imaging because we have a high confidence of which samples are tumor and which are benign. My key advice when learning the technique is to work with your local pathologist so that final tissue diagnosis and report are not compromised.
To target the tumor location, review the MRI images to measure the location above the tumor and find the sequence at which the tumor is most visible in the axial plane. Scroll through the axial images to identify the image in which the tumor is the largest and print the image for reference. In the corresponding coronal image, measure the distance from the base of the prostate to the selected axial position and measure the full length of the prostate from the apex to the base in millimeters.
Then print these measurements and mark the locations of the tumor for reference. After the specimen has been collected, sterilize the laminar flow hood and prostate slicing apparatus with 70%ethanol and weigh the prostate on a standard scale in grams. Then paint the right side with blue ink and the left side of the specimen with black ink covering the full capsule and seminal vesicles with ink to allow discrimination of the surgical margins.
To slice the prostate, place the tissue with the base and apex facing opposite walls of the apparatus with the posterior side down and the anterior side up. Place gold pins around the tissue specimen pushing the prostate inward slightly if necessary to achieve a snug fit and measure the prostate length from the base to the apex to compare this measurement to the prostate length that is measured by MRI. If the prostate has shrunk, adjust the anticipated slicing position by the appropriate percentage of the reduction.
Next, measure from the base to the desired transverse slice and select the pin that sits closest to this measurement to slice around. Wearing chainmail gloves to prevent injury, place the blades of the slicing device on either side of the identified pin and use the spacer to keep the blades five millimeters apart. To acquire the slice, use long strokes to slowly but firmly move the blades downward, forward, and backward confirming by feel that a full slice has been separated before disassembling the apparatus.
Then remove the walls and pins and use gloves to carefully transfer the slice onto a sterile piece of corkboard. After acquiring the specimen, visually inspect the transverse slice for comparison with the axial MRI image. In some cases, the tumor area may appear paler than the surrounding tissue.
Palpate the transverse slice gently. The tumor may feel firmer than the surrounding tissue. Using the axial MRI image as a guide, select one or more areas for sampling and use a six millimeter punch to push down on the tissue area of interest.
Twist the tissue punch on the spot and down against the cork to ensure a full separation using a sharp scalpel to separate the biopsy sample from the specimen as necessary. When the sample has been acquired, remove the punch and use the plunger to eject the sample into the appropriate container for the subsequent downstream analysis. Then ink the holes where the punches were taken in red and note the location of each punch along with the weight of the prostate and any observations about the tissue color and firmness.
Pin the prostate capsule to the cork to prevent bilging during fixation. Submerge the prostate and cork into fixative ensuring the sample is fully submerged. In this representative analysis, of the first 92 cases sampled as demonstrated, 64%of the specimens contained at least 40%tumor and were submitted to the 100, 000 Genomes Project without microdissection.
DNA was extracted and was of sufficient yield and quality in all of the cases and an initial subset of 59 of these samples has been published for comparison with an earlier specimen sampling method. Following this procedure, the fresh tumor samples can be used for either live imaging or culture allowing us to test new biomarkers, drugs, and find out more about tumor biology. Now that we use this method routinely, I've been able to bring forward a project using this tissue for ex vivo culture to look at new combinations of preclinical therapies for prostate cancer.
