Lets say someone goes to the doctor: The doctor sees tumors in the lungs and in the liver. Why does the doctor know that its liver cancer that spread to the lungs and not lung cancer that spread to the liver?
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Radiologists are doctors who look at and issue reports for scans. They’re trained to report scans and have a lot of experience.
In many situations the pattern of the disease points towards where the original tumour – or the primary tumour – is.
The largest lesion is often the primary tumour. Also if then lungs and liver are involved, usually the lymph nodes are also involved so looking at which lymph nodes are enlarged can also help point to wards the primary tumour. Normally the nodes nearest the primary are the largest or most numerous.
Ultimately though, a biopsy is often needed to get a sample to send to Histopathology doctors to look at and help classify the primary. The cell type of the tumour and other features usually helps localise where the cancer started from. It is also essential to give the right treatment as there are so many options these days.
The samples can by Radiologists these days using scans to guide biopsy needles, to try and prevent surgery. The biopsy needles go through the skin to target either lesions in the lung, or the liver, or lymph nodes if accessible. The neck can be a common place to find lymph nodes from lung cancers for example.
But also samples can be taken by respiratory doctors using endoscopes in the airway (bronchoscope) – basically cameras and biopsy needles that can go down the airway to the lung or nearby lymph nodes. Or in the liver biopsies can be taken from endoscope on the food pipe down to the stomach or bowel (OGD-scopes), going through from either the liver or nearby lymph nodes. These often use ultrasound at the end of the camera to help target a lump outside the bowel.
Sometimes though, surgery is needed to take biopsies from the tumour if it’s not accessible or safe to do in other ways.
Sometimes even after Radiology, Biopsies and pathology results the origin of the cancer is still not known. For example the tissue might even be neither lung or liver but actually from somewhere else like neck or skin or bowel but without anything obvious to see on Imaging in those areas. These are called “Cancers of Unknown Primary” and treatment is guided by a best guess of where the primary might have been, and cover those areas of suspicion with treatment.
Chemotherapy and Immunotherapy can be specific to the cancer type even if the location of the primary is not known, and still be effective.
Radiotherapy needs to be localised to the tumour but if there is a high suspicion of where the primary might be,, that area might be treated even if there is nothing to see on Radiology or scoping. For example someone with lung and liver lesions might get radiotherapy to the neck if the suspicion from the biopsy is that it came from there even with nothing to see.
Cancer investigation is a multidisciplinary team approach. Often many doctors and allied health professionals will be involved in the diagnosis and treatment of cancers, but the patient may only meet one or two of those people – often the surgeons and/or the oncologists – while there may be many more people quietly working in the background like the pathologists or fleetingly seen for biopsies like the radiologists.
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