Tuesday, December 2, 2014

Help! There's a lump on my pet! (Part II)

cat carrier
Tira isn't too impressed.
So there's a lump on your pet. In yesterday's post we discussed how veterinarians work out what that lump is. Today we're going to talk about staging and surgery. When it comes to cancer, the two important things you need to know boil down to this: what is it? and where is it? They are deceptively simple questions. Sometimes it takes a number of tests to determine the answers.

Why is surgery required? Surgery is performed for a number of reasons. Sometimes the aim is to achieve a diagnosis, by obtaining a biopsy and exploring the extent of local disease. Often the aim is to cure the patient – by removing all abnormal tissue. In human patients, 60% are cured of cancer by surgery alone1. In cases of advanced or aggressive disease, surgery may be means of relieving pain and improving quality of life (palliation). Surgery may be combined with chemotherapy or radiotherapy to ensure that microscopic disease is not left behind.

What planning is required and why? Surgery is similar to medication in that we can think of surgery like a “dose”. If we under-dose the patient by failing to remove enough tissue, we potentially leave cancer cells behind. If we over-dose the patient, that is, remove too much tissue, we may have complications including delayed wound healing, poor functional outcomes (for example, if too much muscle is removed) or poor cosmetic outcomes. To determine the correct dose, we need to know what kind of tumour we are treating and the likely behaviour of that tumour.

What do we need to know to plan surgery? Firstly it is important to know what the tumour is. A biopsy is sent to a pathologist for evaluation of cells (cytology) or tissue (histopathology). In most cases this provides information on the type of tumour and the grade, which can in turn help us predict how that tumour will behave (for example, is it more likely to spread to distant sites in the body (metastasize)).

Secondly, we need to know where the tumour is – is it isolated to a single anatomical site, such as a lump, or is it present elsewhere in the body, for example metastases in the lymph nodes or lungs. Knowing the location and the extent of the tumour is important in determining the most effective treatment. The process of finding this out is called staging and may involve blood tests, chest x-rays, ultrasound, sampling lymph nodes and even advanced imaging with CT and MRI. This helps us to determine whether and how we can remove the entire tumour, and what additional treatment may be required.

A chest x-ray. This dog has concurrent congestive heart failure and some suspicious looking areas in the lungs.
Can’t you just remove as much of the tumour as possible? Unfortunately this approach doesn’t work well. It can be helpful to think of cancer like a crab sitting on or in the body1. If we remove the biggest part, the body of the crab, but leave the legs behind we’re in trouble. The body of the tumour is often the slowest growing part, while the edges of the tumour (the legs) are the most invasive. If we leave these behind, we may actually be selecting for the most aggressive parts of the tumour – and leaving ourselves without healthy normal tissue to close the wound.

What factors influence the outcome? Aside from the general health of your pet, the best outcomes are associated with slow-growing tumours that have discrete boarders and can be isolated from underlying tissue, small tumour size and a low histologic grade. If we are aiming to cure, our best chance for a cure is the first operation. Surgery may be less successful if the tumour is recurrent, is poorly defined, or has a history of rapid growth1.

It is often said that a chance to cut is a chance to cure for a reason. (In this case its also a chance to sample an awesome guinea pig cake).
Why do we submit the lump for pathology after removal? Following removal, there are two key reasons for having a pathologist assess the lump. First, the diagnosis can be confirmed. Secondly, the pathologist can assess the margins – that is the amount of normal tissue removal along with the lump. Clean margins consist of healthy tissue without neoplastic cells. “Dirty” margins have evidence of cancer cells or microscopic disease.

Are additional treatments required? This depends on the tumour type and stage. In many cases, the tumour is removed and that is the end of the story. If margins are “clean”, there may be no further treatment required. If margins are “dirty”, further surgery may be required. This should be performed as soon as possible to remove the entire previous surgery site. In some cases, chemotherapy or radiotherapy prior to or following surgery may improve the outcome for your pet.

References


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