The first step in the diagnosis of a cancer is to take some samples from it – cancer can only be diagnosed by a pathologist in a laboratory. Although we can be suspicious of cancer based on the physical appearance of a lump or based on an x-ray this cannot be a definite diagnosis. There are numerous ways that we can take samples and there are pros and cons of each method. The simplest method is using a fine needle aspirate to take a small sample – this method is non-invasive and usually does not require any sedation or anaesthetic. However, the sample size is very small and sometimes does not give us an answer. It also cannot grade a tumour, which is how we know how aggressive it is. The second option is to take a biopsy from the mass, either surgically or using a special type of core needle. Using these methods mean that we get more tissue so a more robust diagnosis. The down side is that they usual require sedation or anaesthesia as they are more invasive.
Once a cancer has been diagnosed then it is often recommended to perform further tests to see if it has spread to other parts of the body. This process is known as staging and performing these tests is important for several reasons. Firstly, it often gives us prognostic information, which means that we can predict the outcome of the patient. Cancers with a more advanced stage will often have a poorer prognosis. Secondly, the stage often influences the treatment that is recommended. For example, chemotherapy may be recommended along with surgery for tumours that have evidence of spread. Thirdly, as cancer often affects older animals, staging is important as we may find other medical problems at the same time that could affect treatment.
The type of staging tests that are recommended will change depending on the type of tumour. It is a common misconception that the most advanced type of scan (for example an MRI scan) will be the best test for every tumour. Some tumours do require advanced imaging and in this case a CT scan is usually recommended. However other tumours (particularly those that affect the immune system) do not show up very well on a CT scan in which case and ultrasound scan may be recommended instead. Our patients usually require sedation for a scan to take place as they need to lie still during the procedure. In this situation sedation is actually kinder than restraining a conscious animal as they normally find this more stressful. Occasionally a full general anaesthetic may be recommended due to specific requirements. Staging may also require further biopsy samples to be taken – again this is dependent on the type of cancer that is under investigation. At Wear Referrals we have a complete range of facilities for imaging cancer patients.
A common question from owners is whether cancer will show up on a blood test. The general answer is no – we often perform blood tests to assess the general health of our patients but cancer very rarely shows up on these tests. The only exceptions to this are cancers of the blood such as lymphoma and leukaemia.