Prostate Biopsy Processing

An Innovative Model for Reducing Cost, Decreasing Test Time, and Improving Diagnostic Material

Paari Murugan, MD; Dip Shukla; Jennifer Morocho, HTL; Deanne Smith, PA; Drew Sciacca, PA; Meghan Pickard, PA; Michelle Wahlsten, HTL; Ashley Gunderson, HTL; Badrinath Konety, MD; Mahmoud A. Khalifa, MD; Christopher Warlick, MD

Disclosures

Am J Clin Pathol. 2019;152(6):757-765. 

In This Article

Discussion

The diagnosis and management of prostate cancer is a significant burden on health care systems across the world, given the high incidence and wide prevalence of the disease. Both diagnostic and active surveillance strategies involve systematic TRUS-guided biopsies wherein at least 12 core needle biopsy specimens (modified sextant procedure) are performed per procedure according to current guidelines.[2–5,9] Additional targeted sampling aided by multiparametric magnetic resonance imaging (MRI) studies is progressively more prevalent as well.[10] For one standard case, this typically results in 18 to 42 slides when two or one core(s) per part respectively are submitted. Considerable time, effort, and experience are involved in accurately embedding, sectioning, mounting, and reading the corresponding number of blocks and slides. Furthermore, accurate Gleason grading and quantification of percentage and number of cores involved by carcinoma are critical determinants of patient management and mandatory requirements for prostate biopsy reporting.[11–13] Evaluating intact, unfragmented tissue cores is of considerable importance in this regard. Unfortunately, fragmentation is a common byproduct of standard biopsy processing,[6–8] since the delicate <0.1-cm diameter prostate tissue cores are subject to physical stressors at various points of tissue handling, including transfers from biopsy needle to filter paper, formalin container to tissue cassettes, and during tissue embedding. This is especially pronounced in cores that are inherently fragile due to higher volume and/or grade of cancer as a result of diminished stromal support. Such fragmentation can compromise diagnostic accuracy through errors in cancer quantitation or Gleason scoring Figure 3, thereby resulting in potential patient mismanagement.[9] When translated to ~1,000 cases or more per year for busy urologic practices, the large number of specimens per case and the possibility of tissue fragmentation place a substantial burden on anatomic pathology laboratories and pathologist workload, especially in the face of diminished reimbursement rates. Hence, a pressing need for process innovation exists.

Figure 3.

Examples of potential diagnostic errors due to fragmented and misaligned tissue. A, Error in calculating percentage involvement: two cores, each with less than 50% involvement by carcinoma, may be misrepresented as one core involved by more than 50% tumor. B, Error in determining the number of cores with cancer: one of three cores involved by carcinoma presenting as three of three cores positive for tumor. C, Error in determining Gleason score when each core is scored separately: two cores, each with Gleason 7(3 + 4) carcinoma, fragmented and misaligned to falsely depict Gleason 8(4 + 4) carcinoma in a core.

Our study demonstrated that the multiplex chip protocol offered an effective solution to these issues, demonstrating a significant process improvement. The MC used in our study is a custom-made tissue array that can accommodate six prostate needle biopsy cores in a single scaffold. It is constructed using a proprietary biomimetic material that allows processing and sectioning using standard protocols. The MC can be used at the point of care where the biopsy procedure is performed. The chip is preplaced in a standard tissue cassette between biopsy pads and the needle cores from each location are directly transferred from the biopsy gun into site-designated grooves by capillary action (Figure 1). The cores are examined in situ at the grossing station without need for forceps extraction. Similarly, the chip is directly embedded without disturbing the cores. Both these modifications prevent the possibility of traumatizing the delicate tissue. Grossing, embedding, and sectioning one block instead of six saves considerable time and material and offers a clear advantage over standard processing. In addition, the cores are supported in a single plane, thus making sectioning easier and preventing tissue loss by block facing when poorly oriented tissue cores are encountered.[14] Moreover, the capillary action of the flanking ridges stretches the tissue and increases the diagnostic surface area. Since nonlinear fragmentation and misalignment are obviated by using the MC, the time required to decipher tissue orientation and cancer quantification is conserved. In this regard, it should be noted that although a diagnosis of "cancer involving multiple fragmented cores" is acceptable practice, such an interpretation is less than ideal for patient care and should be considered only when accurate quantification is impossible. In addition, especially in cases with multiple benign cores, the reading time is much quicker, analogous to diagnosing a prostatectomy case on whole-mount sections compared with standard sections. Thus, compared with SP specimens, our study showed an average increase of total biopsy core length by 9.10 mm (P = .0001) with absence of nonlinear fragmentation, thus mitigating factors that reduce diagnostic yield and accuracy. Our study also demonstrated that the use of the MCP resulted in greater than fourfold reduction (P = .0001) in preanalytical time and significant reduction of the slide microscopic examination time.

In addition to reduced storage space for blocks and slides, a factor that is of import in the long run for high-volume laboratories, other apparent advantages of the MC approach may be observed in the following contexts.

  1. Multiplex immunohistochemistry (IHC) stains are routinely used in prostate biopsy diagnosis to support the morphologic impression. The impact of the MC in this regard is underscored in cases where IHC is required for more than one part. The chip array offers the benefit of performing IHC on a single section that covers six tissue cores (similar to tissue microarray sections), in contrast to multiple separate standard protocol sections. Not only does this conserve expensive IHC reagents, but it also offers the distinct advantage of being able to evaluate the IHC features of all tissue cores in the chip in addition to the ones queried. This increases diagnostic accuracy without driving up the cost of testing. Furthermore, correlation of lesional foci between the H&E and IHC stains is precise since block facing due to plane misalignment is absent and multiple identical duplicates can be obtained. This conserves invaluable tissue for research and genetic testing as well.

  2. At present, there is burgeoning interest and research in multiparametric MRI-based detection and targeted biopsies for prostate cancer. A critical aspect of these studies involves stereotactic correlation of tissue diagnosis with the imaging findings to help validate and thus increase the accuracy of MRI assessment. The MC matrix layout allows for specific orientation and organization of the biopsy specimens, which can then be digitally annotated for the location and extent of the carcinoma. This can be accurately extrapolated with the MRI images to create a radiology-pathology fusion image that serves as an invaluable correlation tool Figure 4 .

  3. Whole-slide imaging and digital pathology are expected to play a central role in pathology diagnosis in the near future. Currently, we are in the early days of diagnostic automation using artificial intelligence (AI) platforms. Prostate cancer is at the forefront of these attempts given the fact that it has well-structured grading and quantification schemes.[15] The standardized organization of the cores in the MC matrix will allow AI algorithms to effectively quantify and qualify carcinoma.

Figure 4.

Radiology-pathology correlation from targeted biopsy specimens. A, Standardized, oriented placement of biopsy cores in the MC and digital pathology annotation from designated region of interest (ROI)–2 (malignant areas in red). B, Radiology-pathology fusion images depicting carcinoma sampled from ROI-2.

Several techniques have been explored in the past for improving efficiency of prostate biopsy specimen processing, but the need for a universally adaptable solution is unmet. Multiplexing tissue for histologic examination and immunohistochemical studies using tissue microarray[16] and similar technology are well established. However, these pertain to archived paraffin blocks and are typically confined to the research domain. Multicompartment cassettes for prostate biopsy specimens also have been used,[17] but despite reducing the number of blocks and slides, this method amplifies the other described challenges. Solutions for reducing tissue handling and maintaining orientation, especially by avoiding the embedding process, have been explored in the past, albeit without widespread acceptance. The common denominator in these methods are synthetic sectionable tissue holders. One of these, a proprietary resin cassette (Tissue-Tek Paraform) manufactured by Sakura Finetek USA, offers a multiplex solution for biopsy cores. However, the design of this cassette renders its adaption for prostate biopsy specimens challenging and has thereby not gained widespread acceptance.[18] Researchers have previously reported at conference proceedings their observations on the MC used in our study.[19–22] In concurrence with our results, they have reported significant processing time and cost savings, increased core length, increased cancer detection rate, absence of nonlinear fragmentation, decreased storage space, and increased tissue preservation in the block for ancillary testing. However, these reports could not demonstrate a difference in reading time since the biopsy specimens compared were from different sets of patients and could not be controlled for the presence of carcinoma.

Limitations of our study include the fact that our study design was simplified for logistic purposes and thus sampled only one core per part. Although some urologists do submit specimens in this manner, there are several who sample two cores per part. It is highly probable that the advantages of the MC we observed would be enhanced in the latter scenario due to increased likelihood of tissue fragmentation and misalignment.[8] The other limitation is that one must be vigilant in making sure the MC material does not completely dry out during loading or grossing as this can cause the matrix to become brittle and cause breakage or difficulty during sectioning or result in the cores sliding out. In our experience, the skill required to transfer the biopsy tissue from the needle to the MC is easily mastered after a short learning curve. However, a potential limiting factor could be the initial buy-in from clinical staff responsible for loading the chip in the biopsy suite. While this study was mainly performed to demonstrate a proof of principle, we acknowledge as limitations that the microscopic review was performed by a single genitourinary pathologist and that the possibility of making errors while examining a single slide with multiple cores could potentially be higher than separately reviewing individual cores on a slide.

In conclusion, our study prospectively analyzed various sample processing and quality metrics between the standard histologic processing protocol and a multiplex method that eliminates tissue handling and allows simultaneous processing of prostate biopsy specimens. The latter not only reduced processing time, reading time, and cost but also allowed for potential improvement in diagnostic accuracy by minimizing tissue loss and nonlinear fragmentation. The MC method could also play a foundational role in current and future advancements in prostate cancer detection and diagnosis.

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