Cancer Definitions - A dictionary for pet owners.

The 5 most important words you need to understand

There is nothing more frightening than confronting a diagnosis of cancer. When your pet has been diagnosed with a cancer, it is vital that you understand the language oncologists use.

#1 – Cancer: the ‘Real’ Meaning

Whereas a ‘tumour’ or ‘growth’ implies an abnormal ‘lump’, it may not be overly harmful. To describe it as a cancer suggests that it will not be held back by the body, continuing to invade and/or spread.

To make a diagnosis of cancer, 2 things are needed.

1.    The first is evidence of progression or growth, meaning that the tumour is not a single, unchanging nodule (lump). This may be self-evident for a lump visible on the surface of the body (external mass).

Alternatively, imaging (x-rays, ultrasound, CT, MRI) or surgical exploration may be needed.

In some cases it is based on proof the tumour is invading surrounding tissues after examination under a microscope.

2.    The second component to a diagnosis is seeing the cancer cells themselves. The most reliable method for most cases is a biopsy of a piece of body tissue for examination under a microscope (histopathology).

A simpler alternative is cytology which requires only a needle, with individual cells blown directly onto a glass slide. This test is less reliable in some situations but is less invasive and less expensive.

#2 – Remission: What Does it Mean to be in Remission?

This means a substantial reduction in the amount of tumour present.

There are 2 types - partial and complete.

1.    Partial remission means a reduction in the tumour diameter by 30%. So a tumour that is 10cm wide has to reduce to 7cm wide before we consider it responsive and call partial remission. Therefore, reduction by, say, 10% is NOT considered a response. In the same manner, an increase of less than 20% is not considered progression or growth.

These values reflect the fact that smaller changes than this have not been shown to equate to long survival with most treatments.

“BUT, what if my dog doesn’t achieve remission?”

Just as importantly, some dogs will have much better quality of life without ANY change in tumour size. This is because some treatments like chemotherapy and radiotherapy can ‘shut the tumour down’ for a while leading to less symptoms.

2.    Complete or clinical remission means the tumour is no longer detectable. Whilst this is clearly good, be aware that hundreds of millions of cancer cells can readily hide in tissues without being detectable.

1,000,000,000 cancer cells create a lump less than half an inch wide!

#3 - Cure: the ‘C’-Word We Hope to Hear

Cure means permanent eradication of the tumour!

The real difficulty with such a simple word lies with trying to prove it! In the section above I told you complete remission means we can’t find the cancer. Follow this train of thought and you’ll realise we can’t measure the difference between cure and complete remission. The only way to tell the difference is by waiting for it to come back. After a while, we figure it’s been long enough that the patient is likely cured. Simple as that!

How long is long enough?

We get this answer from previous research. If we know from previous studies most patients without any evidence of a particular tumour after, say, 5 years never have it come back, all patients will then be told they’re cured once they reach 5 years from the last time the tumour was detected.

The one hole in this argument is “tumour dormancy”, in that some people (and it is better described in people than dogs) develop tumour recurrence up to 20 years after treatment.

In these cases it is assumed that the tumour was resident somewhere in very small numbers and unable to grow until ‘something’ stimulated or allowed its growth again.

#4 - Palliation: does this mean we’re giving up?

No! Firstly, the word can mean different things to different people, including oncologists. To some, it is simply non-curative treatment. Most use it talking about treatment that is principally aimed at improving quality of life with little expectation of prolonging life.

By both definitions, pain control is a good example of palliative care. By the first definition, standard treatment for many dog cancers would also be palliative in that cure rates are low for some of the cancers we treat even though those patients may live out much of their remaining lives with excellent quality of life.

However, for most, restoring quality of life and keeping it normal for a markedly extended period is not ‘just palliative’. If your veterinarian mentions this word, you should ask them to explain what they expect the palliation to achieve. Chemotherapy, radiation therapy and even surgery can be all be used for palliation in some situations.

Another important point about palliation is that helping a dog with cancer is not a choice between intensive therapy and palliation. Helping with cancer is about working out the best means to make an individual feel better, and if possible for longer. This will often mean a combination of treatments, some aimed at the symptoms and some at the cancer.

All cancer patients with symptoms should have palliative care IN ADDITION to whatever best helps fight the cancer.

#5 - Curative intent surgery: Why wasn’t my dog cured?

Believe it or not, but successful curative intent surgery doesn’t mean the patient is cured. The aim is to completely remove all visible and surrounding microscopic disease.  Many cancers spread early but may not be detectable elsewhere until much later. If the tumour type commonly spreads early, your veterinarian may recommend chemotherapy even after successful curative intent surgery.

The 5 OTHER important words you need to understand

If you’re comfortable with the first 5 words, it’s time to move on and make sure you’re crystal clear on this lot.

#1 - Malignant: I know it’s bad, but what does it actually mean?

When a tumour is described as malignant, it has the ability to kill the patient. Usually it’s used when the cancer can metastasise, or spread to distant sites in the body. For some it means that they invade aggressively into tissues nearby.

A critical point to understand is when your veterinarian gives you the facts on your pet’s cancer, he or she is describing what is known from previous research. This is important for 2 reasons:

1. each cancer is unique; 2 dogs with 2 cancers of the same type don’t behave exactly the same.
2. you will be given odds not certainty.

For example, high grade (I’ll explain this in a moment)soft tissue sarcomas and osteosarcomas are both malignant cancers and both from the same broad class of ‘mesenchymal’ (meaning connective tissue) tumours. Almost all cases of osteosarcoma in a dog’s leg have spread before they’re first noticed. Yet half the soft tissue sarcomas do not spread elsewhere and therefore the patients can be cured with surgery alone. What’ll really frustrate you is that we can’t (yet) tell which half can and which half can’t.

My point? Malignant means it might have spread, not that it definitely has. Reason for hope.

#2 - Benign: Better than malignant!

A benign tumour is not expected to be harmful other than perhaps by pushing on nearby structures. Some benign tumours can be left alone such as many small, slow growing skin tumours. Others might be best removed because they are (or will) push on something (like an internal organ) to cause pain or decreased function.

A benign tumour should never be ignored.

Once a decision for ‘no treatment’ is made the growth should still be regularly examined. Ask your veterinarian to explain what you can check for so that you can do much of this monitoring at home.

#3 - Grade: are we back at school? We test the tumour and get a given a grade????

This, and the next word ‘stage’ are commonly confused. The grade of a tumour is an estimate of its ability to grow rapidly and metastasise. A high grade tumour is therefore more likely to cause rapid problems.

As an example, think of it a little like drinking alcohol (with apologies to those too young or too clever to drink). A high grade drink has a lot of alcohol and will get you drunk quickly. A low grade or low alcohol drink can still get you drunk but will take longer. My point is that with grade, we’re talking about the drink, not how drunk you are! A dog can have a high grade tumour, one which will kill him quickly without treatment, but it may not yet have made him feel sick.

#4 - Stage: how is this different to grade?

The stage of a tumour is how advanced it is, meaning how big and in how many places it has spread to. To continue the alcoholic drink scenario, stage would refer to how much alcohol you’ve drunk, not the strength of the drink or even how long you’ve been drinking.

So a high stage tumour may be very large or in multiple places. This does NOT mean that it’s been there a long time and does NOT mean that it is growing rapidly.

Therefore, you could make the diagnosis of a high grade, low stage tumour meaning the tumour is aggressive but has been ‘caught’ early. Alternatively a low grade, high stage tumour would be a tumour that may be growing very slowly but is now large and invading nearby tissues.

#5 - Monitoring: Treatment is finished. Now what?

Following completion of a treatment plan monitoring is usually advised, meaning to check at regular intervals for recurrence of the tumour. There is no standard means or timing for this. It is generally a recommendation based on the disease, the patient, and the owner. There are some situations where having a scan done every month is the ideal, and others where your veterinarian can educate you to perform checks yourself.

When monitoring is recommended, it is wise that you enquire what options you will have if the cancer returns. If finding recurrence does not provide avenues for treatment or the need for palliation then perhaps there is less need for frequent visits or expensive tests. On the other hand, to avoid monitoring in cases where it is most useful might cause you to miss a ‘window of opportunity’.

Well done, we’re finished. The 10 words you’ve covered here will make sure you and your veterinarian get along just fine.

Also: could offer a multiple choice quiz and printable certificate on the 10 words???