After many years of mere promise, molecular biology is finally transforming the way we practice medicine. Indeed, “molecular medicine” is the fastest growing area in the “art of healing” and, together with technical advances, is likely to dictate the future of diagnostic and therapeutic intervention for the next decades.

Pathologists are at the heart of patient-sample interrogation and, therefore, the practical application of the molecular knowledge of disease is deeply changing the way we practice pathology. Our world is transitioning from a pure morphological into a morphomolecular discipline,1  a change that represents both a challenge and an opportunity for tissue and cellular pathologists.

In 2004, the term diagnostic molecular cytopathology was coined to bring some cohesion and focus to all the early attempts to apply molecular diagnostics to cytology samples.2  More than 10 years later, the field could not be more robust3 : cytopathology is an integral part of the whole molecular revolution and, in some areas, such as molecular diagnostics of thyroid neoplasias4,5  or the therapeutic pathology of lung cancer,6,7  it is a leading application. Interestingly, this process is also redefining the relationship between cytopathology and histopathology, allowing for optimal use of cytopathology samples.

MOLECULAR CYTOPATHOLOGY—A PARADIGM CHANGE FOR TISSUE AND CELLULAR DIAGNOSTICS

More than a decade ago, clinicians were concerned about the limitations of cytopathology (such as limited volume of paraffin-embedded material precluding large immunohistochemical panels or assessing for stromal invasion) but were unaware of the potential advantages for molecular testing.8  When dealing with complex diagnoses, such as subclassifications of lymphomas or sarcomas, there was a feeling that the “preliminary cytologic impression” had to be confirmed with a “firm” histologic taxonomy. This is depicted in the “pre-2004 paradigm” in the Figure, 1A. This view, which may already have been relatively unfair at the time, has been challenged since then by the application of molecular diagnostic approaches, providing “pathognomonic” evidence of disease, such as the detection of specific translocations in fine-needle aspiration samples from lymphomas or sarcomas. In that instance, the combination of cytomorphology, immunocytochemistry, and molecular cytopathology is adequate for making decisions on further management (see post 2004 paradigm, Figure, 1B). Modern morphomolecular diagnostics that are predominantly based on cytology (such as lung cancer diagnostics, for which cytology samples are becoming a large fraction of tested samples) are a testament to this change, and proof that this new modus operandi could be extended, if needed, into other areas of diagnostics.

A and B, Change of paradigm in the relationship between cytopathology and histopathology after the adoption of molecular testing. The number of pluses (+) represents the degree to which (according to the author) each subspecialty (cytology or histology) attends to the qualities mentioned in the table. Please refer to the text for further explanation. IHC, immunohistochemistry. C and D, The evolution in time, from left to right, of the talents and know-how necessary in modern multidisciplinary team (MDT) discussions to decide on patient treatment and management. Abbreviation: IHC, immunohistochemistry.

A and B, Change of paradigm in the relationship between cytopathology and histopathology after the adoption of molecular testing. The number of pluses (+) represents the degree to which (according to the author) each subspecialty (cytology or histology) attends to the qualities mentioned in the table. Please refer to the text for further explanation. IHC, immunohistochemistry. C and D, The evolution in time, from left to right, of the talents and know-how necessary in modern multidisciplinary team (MDT) discussions to decide on patient treatment and management. Abbreviation: IHC, immunohistochemistry.

Molecular Cytopathology—Present and Future

Since the early days of this discipline, we have emphasized an important premise: that formalin-fixed, paraffin-embedded–based molecular testing, following adequate validation, can be applied to most cytopathology samples.9  Despite early attempts to deny that, it is now part of many national and international guidelines, including those in which cytopathology samples are a large fraction10  and those in which they may be an exception.11  The list of these single-biomarker tests is growing each year, beyond the realm of regular reviews and captured by molecular testing societies (see AMP12  as an example).

However, cytopathology not only seems to be at the forefront of single-biomarker tests routinely but also is positioning itself as a very credible option for the application of complex genomic testing. The main example of this is represented by the introduction of next-generation sequencing in routine diagnostics. At a time in which it is clear that next-generation sequencing should be part of the pathologist's diagnostic armamentarium13  and that it should be adopted by universal health care systems for the wider use,14  the molecular cytopathology community is already creating international networks for the combined validation of this technology and its global applicability,15  proving again the validity of well-curated cytology samples for any type of genomic analysis.

Molecular Cytopathology—The Need for Integrated Teaching

One of the most puzzling aspects of modern pathology is the gap between the increasing importance of molecular diagnostics and the predominantly morphology-based approach of histopathology and cytopathology education and training. In view of the arguments presented here, the need to start incorporating a substantial molecular diagnostic component into the training of board-certified cytopathologists, cytology clinical scientists, and cytotechnicians cannot be overemphasized. Some early models for morphomolecular integration in training have been proposed,14  and colleges and societies with training responsibilities are currently debating a change in curricula. Those coming into the world of cytopathology should receive basic training in the following areas16: (1) DNA—overview, structure, and replication; (2) RNA—transcription, types/structures, RNA polymerases, and regulation of transcription; (3) proteins—amino acids, genes and genetic code, and translation; (4) nucleic acid extraction methods; (5) polymerase chain reaction—optimization, evaluation of techniques, limitations, and troubleshooting; (6) nucleic acid amplification; (7) gene mutations; (8) molecular oncology—clinical interpretation of simple and complex genomic testing; (9) high-throughput technologies; (10) validation and optimization procedures; (11) quality control and quality assurance; (12) regulation in the use of human tissues for diagnostics and research; and (13) core skills in histology/cytology analysis ahead of testing.

CONCLUSIONS

In an era in which most of the developments in health care will be dictated by clinical applications of new discoveries on the molecular basis of disease, the adoption of a molecular diagnostic armamentarium is essential for cytopathologists to adapt to the 21st century. This process is also redefining the relationship between histopathology and cytopathology. In the cytopathology community, there are early adopters of molecular testing, and in some instances true leaders in the advancement of molecular diagnostics. A comprehensive change of existing training programs should allow its broader adoption by the larger cytopathology community.

How important is a given clinical or diagnostic discipline? It is as important as the relevance it has when deciding on patient management at the multidisciplinary team discussion. As the Figure, 1C and 1D, depict, the multidisciplinary team table is becoming more crowded with time. Embracing molecular diagnostics will allow histopathologists and cytopathologists to keep a central role in the therapeutic decision-making around that table, a process that will be good for the discipline and, importantly, good for the patient.

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Author notes

The author has no relevant financial interest in the products or companies described in this article.