LIFESTYLE I VET TALK
Do you need histopathology on a lump if it is surgically removed?
What should I do if my pet has a lump? Lumps and bumps are common in pets, particularly as they get older. Some lumps can be cancerous (malignant) and some harmless (benign) but it is not always possible to determine this by examination alone. What testing is necessary if you find a lump on your pet? If you find a lump, the sooner it is examined by a vet the better. It is not possible to be certain on examination alone whether a lump is cancerous, so your vet will usually want to run some tests.
Cytology This is a non-invasive test method where cells from the lump are aspirated using a needle and syringe, placed onto a microscope slide and examined. Sometimes the diagnosis needs to be confirmed by a veterinary pathologist at an external laboratory. Generally the results will take 1-2 days.
Often your pet will not need sedation to have a sample taken and it can be done during a regular consultation. The limitations are that some lumps are too small to aspirate, sometimes insufficient cells are sampled and sometimes the results are inconclusive. It is frustrating for both vets and pet owners when a result is not diagnostic. Generally if sufficient cellular material is aspirated, the accuracy is around 90% for cytology. Occasionally results can be misleading as the cells sampled may not be representative of the actual mass, so it is important to continue monitoring the lump and have it re-examined if there are changes.
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Histopathology Histopathology involves taking a tissue sample of the lump by either removing a piece of tissue (incisional or punch biopsy), or surgically excising the whole lump (excisional biopsy), and sending it to an external laboratory for analysis. Results take approximately 5-7 days. Usually a general anaesthetic is required, though sometimes sedation and local anaesthesia is sufficient. An excisional biopsy is carried out in areas where a margin of healthy tissue surrounding the lump can be easily removed, to minimise the chance of cancerous cells being left behind. If the lump is located in a difficult area such as a toe, where there is very little skin, a punch biopsy is preferred. If a toe tumour biopsy result shows that the mass is particularly aggressive, then it may be preferable to amputate the toe to ensure the entire cancer is removed. An advantage of histopathology is that some tumours can be graded to further determine the likely prognosis and best course of action after surgery. For example, most cell tumours of the skin have three grades, all of which carry a different prognosis. The pathologist can also determine whether the margins are clear of any cancerous cells or if further surgery is required.
If a lump is surgically removed, histopathology is worthwhile as some lumps are locally aggressive and others spread internally. In most cases it is not possible to determine what the behaviour of the tumour is by examining it with the naked eye. Knowing what type of lump it is can give peace of mind if it is benign, or allow further tests to be done if it has spread. Histopathology may not be required if it is a foreign body reaction lump, an abscess, or a lipoma (benign fatty lump which can be confirmed with cytology), but this is up to your veterinarian.
What tests can be done if the lump is malignant? If your pet has a malignant lump, histopathology will show what type of cancer is present and the behaviour of the tumour. Sometimes surgery is curative and no further testing is required. In these cases, if the margins are clear of any cancerous cells, monitoring the surgical site may be all that is necessary. If the cancer has a high risk of spreading to lymph nodes, abdominal organs and/or chest, then aspirating any enlarged local lymph nodes, chest radiographs and an abdominal ultrasound will show if there is any evidence of metastases. This is known as cancer staging. Immunohistochemical staining may be an option for some tumour types with varying behaviours depending on certain mutations that may be present. This gives further information about the expected prognosis to decide treatment recommendations. A consultation with a specialist veterinary oncologist may also be recommended.
Dr Gretta Howard. Veterinarian Twitter: @ DrGrettaVet
