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The role of the histopathologist is now changing. Previously, observing cells and tissues microscopically and identifying the features that characterise malignancy or other disease processes was sufficient to make a diagnosis.

However, we now know that this is not the case and the ability to look inside the individual cells at the genetic material, constituents and proteins etc. has enabled us to make a much more accurate diagnosis helping us to understand more about what causes the disease or cancer and potentially how we can treat it.

This has resulted in some significant changes to clinical practice and diagnostic pathways. This is the era of ‘molecular pathology’ and it is the histopathologist who is leading these changes and ensuring that they now feature within clinical practice.

Molecular pathology is a very useful tool that can help you to provide a diagnosis for a case where the histopathology is actually very challenging. We are also faced with the frequent occurrence where cancers can look very similar to each other microscopically but genetically they are very different and therefore require very different treatments; molecular pathology can help identify this differentiation.

There are dozens of different molecular tests that are available for the histopathologist to use; these include different sequencing methods (whole genome, whole exome, targeted panel sequencing, RNA sequencing etc.), fluorescence in situ hybridisation (FISH), mass spectrometry and immunofluorescence to name a few. You also may be asked to assess tumour samples for the percentage of tumour cells and the level of cellularity – these two factors can make a big difference to the accuracy of the molecular results. 

Molecular pathology now features as a prominent part of the training pathway for histopathologists and also features within the examinations. If you become a histopathology trainee you will be expected to engage with molecular pathology from the beginning; many cases will now have associated molecular test reports to interpret and getting to grips with these at an early stage to give you lots of experience is recommended. Also, make sure you can spend some time in a molecular lab to learn more about how the techniques are performed and utilised. It is a fascinating field! 

The important message is that molecular pathology is not replacing histopathology. The histological review and interpretation of a case remains an essential part of the diagnostic pathway and it would not be possible without it. However, molecular pathology is another tool in the histopathologist’s toolbox to help bring all the jigsaw pieces together to make an accurate diagnosis for a patient and ensure they start on the correct treatment pathway. Look out for the BDIAP Molecular Pathology Study Day – an opportunity to learn more about the different tests and how to interpret the results for all the major histopathology specialties.