An Evaluation Of An Automated Platform For The Histological Assessments Of Non-Melanoma Skin Cancer: Dr Guy Orchard Gives An Analysis Of An Innovative Approach To Improve Efficiency And Accuracy Of Frozen Tissue Sectioning
Skin cancer and in particular, non–melanoma skin cancer (NMSC), has been steadily increasing. The basal cell carcinoma (BCC) accounts for >80% of that recorded within the UK. These tumours can occur anywhere on the body, but are more commonly seen in sun exposed sites, such as the face, head, neck and ears. It is also the case that BCC’s can occur at the sites of former burned tissue, scars or ulcers that have damaged the integrity of the skin.
How have the demographics of NMSC changed over time?
As a junior biomedical scientist, I recall seeing histology request forms for BCC’s, mostly on behalf of patients in their 60’s or over. As time has gone by, we have seen the incidence of NMSC rise. I now manage a large Mohs laboratory, one of the largest of its type within the UK and I see BCC’s in patients in their early 30’s and 40’s. A large majority of these younger patients, in spite of our understanding of the effects of sun damage on skin, are strict ‘sun worshippers’, so have increased levels of exposure to sunlight and more specifically the ultraviolet wavelengths UVA and UVB.
Mohs practice within the UK has been expanding steadily over the last decade. Classically, Mohs procedures have the benefit of minimal excision margin clearance and therefore improved preservation of the surrounding uninvolved tissue. In addition, complete tumour clearance following Mohs procedures is assured with accuracy values of over 95%, which remains unmatched by any other patient management approach in skin cancer treatment.
Current equipment for frozen section analysis
In conventional cryostats the method is fraught with inaccuracies including tissue distortion and, most significantly, uneven embedding at the chuck face (the place where the tissue meets the cryostat knife for sectioning) which leads to inadequate and inconsistent tissue orientation problems. These issues become more apparent the smaller and more fragile the tissues are.
The increased pressure to meet TATs has led to the popularity of liquid nitrogen because it has the benefit of reducing the freezing time and the number of freezing artefacts. However, it is often less precise in terms of accuracy of tissue orientation.
A wide range of devices currently produced have concentrated on the flattening of tissue at the surface of the chuck prior to tissue sectioning in an attempt to improve accuracy. However, simply applying a flattening force across the tissue surface during the freezing steps is not always the answer, as tissue composition often affects the ability to lay such tissue down flat without curling or folding. The new generation of embedding devices will need to combine benefits of rapid freezing with concepts of tissue flattening and good orientation. Orientation of tissue will also depend on good visualisation as well as manipulation of the tissue during the freezing process. The issue is a complex one!
A total of 250 blocks were embedded on the PrestoChill and stained on the Presto benchtop processor/stainer. All the tissues selected were assessed in parallel with conventionally frozen tissue to compare and contrast the quality, speed, efficiency and accuracy of both the devices. Figure 1 illustrates the key components and features of the device.
How can a modern piece of equipment manage these variables and perhaps improve efficiency and speed?
In June 2016, Menarini approached Viapath’s laboratories at St. John’s Institute of Dermatology to undertake an evaluation of some new pieces of equipment; the PrestoChill Cryoembedding System and the Presto automated processor/stainer. These two devices have efficiencies of speed over conventional manual methods of frozen tissue section production and staining. Manufactured for use in all forms of frozen section work, both pieces of equipment are designed to be used in a combined unified approach to the histological assessment of frozen section production and subsequent Hematoxylin and Eosin (HE) staining. This includes their application in a host of specialist histological procedures that, due to their complexities, require a more precise tissue analysis.
The use of an optimising cryoembedding compound called MCC, in conjunction with PrestoChill paper to rest the tissues on before freezing, are new developments (figure 2). The speed of embedding was confirmed to be no more than 60 seconds with all the tissues tested. There are also four embedding wells (figure 3) which increases the speed at which multiple tissue slices can be assessed. The PrestoChill device has shown that complex tissues can be embedded correctly and effectively. The options of wells with deeper depths can be used and easily inserted to replace the normal wells provided with the machine, which is beneficial with embedding denser or thicker tissue pieces. Having embedded and sectioned the tissues, the use of the Presto processor/stainer device presents more features (figure 4).
The device can handle 6 slides (figure 5) at a time and the fixation, clearing and dehydration steps were consistently achieved within 1 minute on all the tissue sections stained. The HE staining itself is efficient and the elimination of lengthy washing steps enables the speed of staining to be, on average, less than 3 minutes. Programme adjustments can be easily made to lengthen staining steps to account for operator choice, a surgeon’s preferences for staining intensity and contrast, and thicker tissue sections.
The future of frozen tissue sectioning
These complementary devices are very exciting developments in the field of fresh frozen section preparation and staining. They represent a comprehensive approach to tackling a whole gambit of technical challenges faced in producing good quality and well-stained frozen sections. Within the UK, such devices are likely to gain exposure within the field of Mohs procedures, mainly because of the evident improvements in speed and efficiency. The clean and compact nature of both devices also embraces benefits in the LEAN environment of laboratory design. The benefits of an almost fully automated process are improved standardisation of practice and, ultimately, improved overall quality of performance.
History tells us a lot, a brief glance back over the last 20-30 years within the field of tissue and cellular science has shown us how automated platforms have been embraced and have standardised practices generally for the better. Perhaps it is now time to review this in the light of our frozen section work too.
For further information please contact:
Dr Guy Orchard, Consultant Grade Biomedical Scientist/Laboratory Manager
Email: guy [dot] orchard [at] viapath [dot] co [dot] uk (subject: pathology%40viapath)
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- Orchard GE, Shams. M. Dermatofibrosarcoma protuberans: dealing with slow Mohs procedures employing formalin fixed, paraffin wax embedded tissue in a busy diagnostic laboratory. Br. J. Biomed. Sci.2012: 69 (2): 56-61.
- Orchard G. Mohs and the benefits of new embedding and staining systems. Pathology in practice. 2016. August :1-4.
- PrestoCHILL for high-quality frozen sections- Milestone Medical. (www.milestonemed.com.products)
- Presto Processor/Stainer- Milestone Medical (www.milestonemed.com.frozen-sections)