Biopsy
Taking a small piece of the suspicious tissue so a pathologist can examine it under the microscope. It is the only way to confirm a cancer diagnosis and to learn its type and markers.
Biopsies range from a fine needle drawing up cells, to a core needle removing a sliver of tissue, to surgical removal of the whole lesion; the sample is fixed, sliced, stained and read by a pathologist, and today also tested for protein markers and sequenced for mutations. Tissue is precious and finite, and a single biopsy samples one spot of a tumour that may vary from place to place and change over time, which is why repeat biopsies at progression and blood-based liquid biopsies have become important. Biopsies carry small risks (bleeding, infection, rarely tumour seeding) and some sites, such as the pancreas or brain, are hard to reach.