For cancer diagnosis, there is biopsy, an invasive technique. However, PET CT, SPECT CT, MRI are non-invasive. Do oncologists still require the use of biopsy to ascertain type of cancer, i.e., to confirm the presence or absence of malignancy? If so, why?

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In many cases yes, a tumor must be biopsied in order to determine exactly what type of tumor it is. Advanced imaging can, in some cases, diagnose a specific type of tumor. However, there are many chemotherapy agents that are very specific not just to a particular tumor, but a particular tumor with certain genetic factors (such as presence or lack of specific receptors), so it is impossible to plan the best treatment without tissue.

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  • @CareyGregory There is a paucity of free, open-access literature from which to cite for basic topics such as this. It is possible to cite multiple studies that reference a particular genetic marker, but in general those references are too high-level for this specific question. – RudyB Jun 13 '20 at 20:50
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    I think a biopsy is usually ordered after these scans. I had PET then CT then biopsy. Chemo and radiation for the cancer, then two years later the routine CT showed something, got a PET and then it was still necessary for a biopsy ( MDAnderson- presumably they know what is necessary). – blacksmith37 Jun 13 '20 at 20:57
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    @RudyB I understand and what you added is perfectly sufficient. We don't need a doctoral thesis level of citations, just a basic sanity check or two. – Carey Gregory Jun 14 '20 at 4:37
  • @blacksmith37 The order depends upon multiple factors. In my practice, I can literally get a CT performed in minutes if I really need to (usually for strokes and traumas), and some days I can get an MRI done within half an hour (but almost always only for stroke or spinal cord compression). Granted, I have not ever ordered a PET-CT, those may take some time to arrange or require travel. Interventional radiology also may take some time and/ or require travel in order to get a biopsy performed (or general surgery, or pulmonology, etc.). – RudyB Jun 15 '20 at 0:04

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