Tumour heterogeneity and the assessment of expression of proteins for targeted biological therapies

With the development of new targeted biological therapies for cancer, such as trastuzumab, cetuximab and imatinib mesylate; there is an increased demand for the histopathology testing of tumour tissue for these targets. This testing demands a new paradigm that takes account of the area of the primary tumour which is most likely to have metastasized, which contrasts with conventional grading of tumours on haematoxylin and eosin (H&E)-stained sections. We present cases which illustrate this and review some of the literature on this topic.