Dermatopathology, then and now – have we travelled?

Keywords::

• dysplastic nevus
• molecular diagnostics
• quality assurance
• sebaceous neoplasms

James Bond is not the only one that turned 50 in 2013 [101]. This year also marks the 50th anniversary of the American Society of Dermatopathology, which sets the theme for this editorial. Is dermatopathology today any different from what it was some 50 years ago? Some fundamentals remain the same – we still need a microscope and we still need a pair of trained eyes. So what has really changed?

The dysplastic nevus

Literature is replete with evidence suggesting that dysplastic nevi, a subset of nevi with distinct histologic features, are risk factors for malignant melanoma. These include epidemiologic data indicating an increased prevalence of dysplastic nevi in patients with a family history of melanoma and that over 50% of persons with a dysplastic nevus have a history of melanoma [1]. Furthering this notion, persons with a history of malignant melanoma have been shown to be more likely to have a dysplastic nevus that exhibits moderate to severe cytologic atypia versus one that exhibits mild atypia, and the estimated prevalence of histologic melanocytic dysplasia is approximately 10% in population-based samples but increases to 34–59% among patients with a family history of melanoma [2]. Thus, a dysplastic nevus has come to be synonymous with a pre-neoplastic lesion in the sense that it is believed to be an essential stage in the multi-step cellular evolution to malignant melanoma.

Several observations indicate that a key event in the development of malignant melanoma is activation of the RAS/RAF/ERK pathway with activating BRAF mutations found in up to 50–70% of melanoma [3]. We have previously shown that the BRAFV600E mutation is also present in approximately 26% of dysplastic nevi [4]. Of interest, we also found that 42% of these were histopathologically mildly atypical, implicating mutation of this gene and activation of this pathway as a crucial step in the initiation of melanocytic neoplasia. However, we also know that melanocytic nevi can be relatively indolent for decades despite the presence of activating BRAF mutations [5]. This raises the possibility of additional, possibly co-operating events that are crucial to and responsible for transforming a nevus containing a BRAF mutation into melanoma. We have previously shown that enhanced expression of the tumor suppressor IGFBP7 in oncogenic BRAF positive nevi and, loss of expression in both primary and metastatic oncogenic BRAF positive melanomas identifies hypermethylation of the IGFBP7 promoter as a key event [5]. This suggests that since BRAFV600E positive nevi, unlike BRAFV600E positive melanomas, express IGFBP7, a powerful tumor suppression mechanism remains intact in nevi following an initial oncogenic event [5]. We found disparate expression of IGFBP7 in BRAFV600E positive dysplastic nevi (enhanced in 56% and diminished/absent in 44%) indicating that the behavior of oncogenic BRAF in dysplastic nevi unlike that in malignant melanoma does not appear to consistently induce senescence/apoptosis through pathways mediated by IGFBP7 lending credence to the concept that from an oncogenic BRAF perspective, dysplastic nevi are biologically perhaps no different from a nevus without atypia. More importantly, they challenge the earlier concept of dysplastic nevi being the most common precursor lesions of malignant melanoma.

Sebaceous neoplasms & Muir-Torre syndrome

The occurrence of sebaceous gland neoplasms such as adenoma, epithelioma and carcinoma is clinically significant because of their association with Muir-Torre syndrome (MTS). MTS is usually the result of germline mutation in one or more of the DNA mismatch repair genes (MMR). MMR genes commonly implicated include MSH-2 and MLH-1 and, more recently, MSH-6 [6]. Studies in MTS patients indicate that lack of expression of either MLH-1 or MSH-2 is associated with MSI in 100% of cases while maintenance of expression of both is predictive of microsatellite stability in 93% of the cases. Increasing evidence support the use of immunohistochemistry (IHC) as the initial screening test. These include data reinforcing the sensitivity and ability of IHC to detect the involved MMR protein, reproducibility of results using this methodology and a good correlation between results from IHC and microsatellite instability (MSI) analyses. Additional minor, yet practically relevant, factors relate to ease of the methodology which translates to a rapid turnaround time (TRT). In contrast to IHC, MSI analysis is complex, expensive and cumbersome to perform. As a consequence, the TRT for results using this technique is typically anywhere from 7 to 10 days. More importantly, the presence of MSI is not reflective of the specific gene defect present.

Based on our recent experience, a judicious diagnostic approach is the following; when a patient is diagnosed with a sebaceous neoplasm, especially if young and/or the neoplasm is located outside the head and neck area, then the initial screening tool to identify patients with MTS is to do IHC to check for the expression of MSH-2, MLH-1 and MSH-6 [7]. Lack of expression of any of these proteins should then be followed by germline mutation analysis for the proband and his/her family members to confirm IHC results. All family members with the mutation should then be put on preventive cancer screening programs. If MMR proteins are intact, and the index of suspicion for MTS is still high, then MSI analysis can be done as a second-line screening tool. If MSI is detected then this can be followed by germline mutation analysis. Thus, the utilization of IHC as a screening tool in MTS has facilitated recognition of ‘high-risk’ patients or those with a propensity for the development of visceral malignancies which, in turn, allows for the timely implementation of cancer prevention programs.

Quality assurance in dermatopathology

The Accreditation Council for Continuing Medical Education® (ACCME) recognized early enough that the professional responsibility of physicians requires continuous learning throughout their careers, appropriate to the individual physician’s needs. Thus, professional motivation led the American Society of Dermatopathology in 1974 to approve the establishment of a program for quality assurance (QA), the first of its kind in dermatopathology, which was implemented a year later [8]. In the early years, a ‘hands-on’ approach was utilized in which enrolled participants receive a set of prepared slides of ‘unknowns’ for interpretation in order to evaluate their diagnostic ability. The most obvious disadvantage of this method was that glass slides were prone to breakage. Others included medico-legal implications associated with making recuts as the deeper cuts might reveal pathology that was not evident to the pathologist who signed out the case initially. In keeping with digital age, the next step implemented was a digitized QA program. In this, enrolled participants received two CDs: the first containing digital images of representative diagnostic sections of unknown cases and the second containing additional images of special stains relevant to each case, case answers and case discussion. Program cases were formatted in HTML (the predominant markup language for web pages) and designed using the program Macromedia Dreamweaver MX. The CDs’ user-friendly format enabled participants to view the cases on an individual, case-by-case basis, by simply opening them in their web browser (e.g., Internet Explorer, Netscape Navigator, etc.). The obvious advantage of this method was that it enabled all participants to receive the exact same sample (even testing field!). Second, the repertoire of conditions represented in the QA program was unlimited as all that was required was one tissue section containing the lesional area. Thus, from a practical perspective, it enables testing of entities/areas that had not been surveyed before. The design and layout features themselves provide countless, if less obvious, benefits. Clinical images were included, along with a case’s histology images, and the programming allowed participants to view all of a case’s images in one screen. The obvious disadvantage was that the image was a static one and entirely dependent on the photographer’s ability. Moving on to where we are now, we now have a virtual QA program in which slides are scanned by whole slide imaging (WSI), a technique that automatically images the entire slide at high speed and produces high-resolution facsimiles. Images are compressed during the capture process in a multi-layered JPG2000 format and stored in a web-based server. Enrolled QA participants can then access the server (and therefore the images) online through individual, password-protected accounts, eliminating security concerns. WSI is now becoming ubiquitous in educational settings as an ancillary teaching adjunct.

Molecular diagnostics in dermatopathology

Although best befitted by a review devoted to itself alone, this editorial would be incomplete without a final few words on the subject of molecular diagnostics. While molecular diagnostics has had its greatest impact in the diagnoses and prognostication of melanocytic tumors, it has also contributed to the significant advances made in the diagnoses and sub-classification of other lineage-unrelated cutaneous tumors [9]. Techniques such as FISH, reverse transcriptase polymerase chain reaction (RT-PCR), gene microarrays and comparative genomic hybridization are now being used for a variety of reasons. While most of these are primarily research-based techniques, the Abbott FISH probe is now US FDA approved and is used in an increasing number of centers to distinguish malignant melanoma from banal nevi [10]. Other than diagnosis, laser capture microdissection in combination with PCR and gene sequencing has been used to determine the biological significance of ‘nevic’ aggregates underlying primary cutaneous melanoma [11]. Based on their BRAF profiles alone, results of one such study indicate that when they occur concurrently, they are best managed as one entity [12]. Thus, the application and utility of molecular diagnostics appears to be wide and far reaching.

I began with the tantalizing title of: dermatopathology, then and now – have we travelled? The response is a resounding yes – have we travelled!

Financial & competing interests disclosure

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.