A 63 year old woman presented with a one month history of difficulty speaking and imbalance. She had been diagnosed with breast cancer two years earlier and had been treated with surgery, chemotherapy, and radiotherapy. This was followed by a year of trastuzumab (Herceptin) and continuous tamoxifen treatment. Magnetic resonance imaging (figure⇓) of the brain showed that she had a large solitary rounded enhancing mass lesion in the left inferior parietal lobe. It was present at the grey-white interface and there was extensive surrounding vasogenic oedema. The lesion was avidly enhanced after the administration of gadolinium (not shown). The appearances were suspicious of a solitary brain metastasis, but the differential diagnoses included a primary intrinsic malignant brain tumour. T2 weighted axial magnetic resonance image of the brain showing a rounded mass lesion in the left inferior parietal lobe After starting steroids, she underwent neurosurgical craniotomy and a gross total resection was achieved. Histological examination showed extensively necrotic metastatic carcinoma. On immunohistochemical analysis, the tumour cells were strongly positive for E-cadherin, oestrogen receptors (ERs), and progesterone receptors (PRs). Human epidermal growth factor 2 (Her2) amplification was identified by fluorescence in situ hybridisation. ### 1. What is a tumour biomarker? #### Answer Tumour (or cancer) biomarkers are biological molecules that suggest the presence of cancer in a patient. Biomarkers may also be used to characterise known tumours. They are either produced by the tumour itself or by the body in response to the tumour. #### Discussion The National Cancer Institute defines a biomarker as “a biological molecule …
