Pathologic Assessment of Radical Prostatectomy
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The pathologic assessment of radical prostatectomy, like any pathologic evaluation, is based on gross and histologic examination. Good fixation, orientation, and delineation of surgical margins are critical in achieving optimal results. [1, 2, 3]
This article describes a method for tissue preparation of radical prostatectomy that allows the production of whole-mount sections and the collection of fresh tissues for research without the use of specialized equipment. Using this technique, the authors’ laboratory of 5 technicians can adequately process over 600 prostatectomies per year, admixed with an additional 5000 other surgical specimens.
If fresh tissue is required for research purposes, the tissue may be harvested in the fashion described herein. The unfixed prostate gland is weighed and measured in 3 dimensions following removal of the left and right seminal vesicles. A horizontal section is cut through the gland, posterior to anterior, perpendicular to and through the prostatic urethra at about the level of the verumontanum (see the image below).
A hinge of tissue is left anteriorly. If the tumor is visualized macroscopically, this is helpful, and the tumor tissue can be targeted. In most cases, no tumor is visualized, and random sections of the posterior lobes and transition zone may be collected with particular reference to the preoperative needle biopsy results.
Tissue is harvested by taking 0.5mm- to 1mm-thick horizontal tissue sections from the cut surface, as shown above, and immediately storing them at minus 80°C. Alternatively, samples may be taken from the cut surface by scraping cells with a surgical scalpel [4] or with punch biopsies. [5] To avoid distortion of the specimen during fixation, the prostate gland is then reassembled using metal skin staples (see the image below). Careful attention must be paid to the capsule, whose cut surfaces are opposed and then stapled together.
Optimal fixation is critical for the histologic assessment of prostate cancer, and most artifacts related to the histologic or immunohistologic evaluation are a manifestation of poor tissue fixation. [6] In the authors’ laboratory, a proprietary glutaraldehyde-based fixative (Solufix) is used, but in other laboratories, a high-quality formaldehyde or an alcoholic formaldehyde may provide suitable fixation.
Because penetration to the center of the specimen is slow, particularly since cross-linking of proteins occurs during fixation of the prostatic capsule, an injection of fixative through the capsule is recommended. [6, 7] This is particularly important for glands larger than 30cc. The authors use an 18-gauge needle to inject the gland at multiple sites using a 10 or 20cc syringe (see the image below).
Extreme care is required to avoid needle-stick injuries, and staff training is critical in avoiding such accidents. Wire-mesh gloves or tongs to support the tissue can be used. Following an injection of fixative, the prostate is then immersed in a bath of fixative and allowed to fix for 24 hours at room temperature.
After removal from the fixative solution, the specimen is dried, and the left and right lobes are painted with different colors using an acrylic-based paint (see the image below) to orient the gland and to clearly delineate the surgical margins. Many different colors of acrylic paint are available at most artist shops, but care must be taken in the selection of brands whose pigment is xylene fast.
After the gland is painted, the prostate is dried with a household hairdryer until the acrylic paint is solid. Once dry, the prostate can be sectioned (see Tissue Sectioning and Embedding).
The prostatic apex is separated from the gland approximately 2mm from the apical surface. To enhance the detection of the apical surgical margins, the apical portion is then bread-loafed from the left to the right in 3mm slices, and the left and right apical tissues are placed in separate cassettes. In a similar fashion, the bladder neck (base) is cut, sectioned perpendicularly, and stored in separate cassettes. The seminal vesicles are sectioned vertically, and a single section from base to tip of each seminal vesicle is blocked (1 or 2 cassettes). The remainder of the gland is cut in a stepwise fashion.
The authors’ laboratory uses a standard cutting board on which 2 glass rods (4mm in diameter) are stuck with epoxy resin. The prostate gland is placed between the rods that are used to guide a standard laboratory disposable blade, allowing whole-mount sections to be cut at exactly 4mm intervals.
Once sectioned, the prostate slices are labeled with India ink in alphabetical order (eg, A, B, C) to orientate them with respect to the superior and inferior surfaces plus the anterior and posterior margins (see the image below); they are then refixed for another 6 hours. These 4mm whole-mount sections are then divided into halves (or quadrants, in a large gland) to fit into standard-size cassettes used for paraffin-embedding. Careful labeling is critical to allow the technicians to correctly orient the sections.
Sections are cut and placed on large glass slides, with care taken to oppose the left and right sections such that they appear as a single whole-mount section.
This technique obviates the cost involved in purchasing specialized equipment, such as sledge microtomes, allowing sectioning of almost all prostate glands to be done on standard rotary microtomes. No special blocks are required, and large cassettes are used only if required for the storage of whole mount sections during processing. Total embedding of radical prostatectomy specimens in this manner was first described by Stamey and colleagues in 1998. [8]
Standard hematoxylin and eosin (H&E) stains are performed on all whole-mount sections, all apical and bladder neck sections, and the single embedded sections from each seminal vesicle. Immunostains are generally not required for standard, routine histologic interpretation.
The morphologic parameters usually assessed on H&E are those listed as category 1 factors (well-supported by the literature and generally used in patient management) in the College of American Pathologists 1999 Consensus Statement on prognostic factors in prostate cancer. [9] These parameters include Gleason score, pathologic tumor stage (derived using the tumor, node, metastases [TNM] classification system), and surgical margin status. [10, 11]
While these parameters can be adequately assessed using a systematic partial submission strategy, embedding of the entire gland and use of whole-mount sections allow an evaluation of potential new prognostic factors. These factors include those currently listed as category 2 (supported in the literature but requiring further validation in larger, multivariate studies), such as tumor volume, [12, 13] or category 3 (relatively or completely untested), such as the zonal origin of the tumor (peripheral, transition, or central zone) [14, 15] and tumor multifocality.
Cutting the entire gland into 4mm slices and reorienting the tissue sections to reconstruct each whole-mount slice allow a simple calculation of tumor volume. The areas of cancer on each section are colored under low power (X15) using a fine, indelible, felt-tip marker pen. A scanned image of the tissue sections is obtained (see the image below), and a computerized image analysis is used to calculate the overall area in cubed centimeters of cancer on each section.
The cancer areas are multiplied by a factor of 1.24 to correct for tissue shrinkage during fixation and then either by 0.3cm for the sections of apex and bladder neck (base) or by 0.4cm for the whole-mount, transverse sections. Total tumor volume is obtained by adding the calculated areas. [16]
Occasionally, and despite an accurate preoperative diagnosis, prostatic adenocarcinoma is not identified. A review of preoperative core biopsies is indicated to confirm the diagnosis. levels may be cut through blocks in areas of high-grade dysplasia (eg, prostatic intraepithelial neoplasia, or PIN) if clinically indicated. The absence of carcinoma following microscopic carcinoma on core biopsy is well described, [17, 18] and no further laboratory action is necessary.
The technique described herein provides a simple, cost-effective method of allowing whole-mount examination of the prostate gland. Using this technique allows the authors to easily process 3-4 specimens daily as part of a busy tissue pathology laboratory without resorting to any specialized or expensive equipment. The entire gland is examined in each case with good orientation and the opportunity to collect fresh tissue if desired without impact on the quality of the sections.
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Cao D, Hafez M, Berg K, Murphy K, Epstein JI. Little or no residual prostate cancer at radical prostatectomy: vanishing cancer or switched specimen?: a microsatellite analysis of specimen identity. Am J Surg Pathol. 2005 Apr. 29(4):467-73. [Medline].
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Ronald J Cohen, MB, BCh, PhD, FRCPA, FFPATH Director of Pathology, Uropath Pty Ltd; Clinical Professor, School of Pathology and Laboratory Medicine, University of Western Australia, Australia
Ronald J Cohen, MB, BCh, PhD, FRCPA, FFPATH is a member of the following medical societies: Royal College of Pathologists of Australasia
Disclosure: Nothing to disclose.
Liang Cheng, MD Professor of Pathology and Urology, Department of Pathology and Laboratory Medicine, Indiana University School of Medicine; Chief, Genitourinary Pathology Service, Indiana University Health
Liang Cheng, MD is a member of the following medical societies: American Association for Cancer Research, American Urological Association, College of American Pathologists, United States and Canadian Academy of Pathology, International Society of Urological Pathology, Arthur Purdy Stout Society
Disclosure: Nothing to disclose.
Beverley A Shannon, PhD Research Scientist, Tissugen Pty, Ltd, Western Australia
Disclosure: Nothing to disclose.
Pathologic Assessment of Radical Prostatectomy
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