Investigation and Treatment of Cancer


Investigation and Treatment of Cancer in Cats and Dogs

The investigation and management of cancer in pets is relatively straightforward and follows a similar pathway for all patients, with a few basic rules followed. When investigating a tumour, we never forget that the tumour is attached to a patient, and that careful consider is to be given to the care and needs of the pet and owner. This approach ensures that owners are fully informed and that plans for investigation and management of the pet are made following a detailed discussion.

Investigation and treatment of cancer follows three steps; investigation and care of the patient, investigation of the tumour and identification of the most appropriate therapy. This ensures that the patient is put first, the disease second, and the proposed therapy third. We always make every effort to ensure that we have a correct diagnosis before begging therapy and that the patient will be able to tolerate the treatment prior to starting it.


General assessment

Our initial approach is to assess the patient and then assess the tumour. Each patient and tumour is different, and so the investigative approach is tailored to the individual, although the same basic principles apply.

For each patient it is necessary to gain an accurate assessment of the long-term outlook. The prognosis for animals with cancer depends on a number of factors:

  • The microscopic or histological type of the tumour, i.e. what cells are in the tumour?
  • The grade of the tumour, i.e. how aggressive do these cells look under the microscope and how does the tumour behave e.g. benign or malignant?
  • The clinical stage of the tumour, i.e. is there any evidence that the tumour is affecting more than one site in the body and how is it affecting the patient now?
  • The presence of tumour-related complications (so-called ‘paraneoplastic syndromes’)
  • The presence of other diseases.

Our approach to gaining a prognosis is to assess the general health of the patient and identify any other diseases presence. Once the presence of a tumour is confirmed, as much information possible about the tumour with be gathered whilst identifying how the tumour is affecting the patient.

The basic principles in assessing a patient with cancer are:

  • Tumour measurement
  • Staging the tumour
  • Assessment of the patient’s general health and fitness
  • Diagnostic imaging (e.g. X-rays, ultrasound, CT scan, MRI scan)
  • Blood samples to look at the various blood cells and other substances in the blood (haematology and biochemistry)
  • Examination of samples from the tumour or other sites, either samples of cells (cytology) or tissue (histology).

Two important factors are the grade and stage of the tumour, both of which must be assessed.


Tumour Staging

One of the most important ways to assess a patient with cancer, is the ‘TNM’ system. This involves:

  • Examination of the primary Tumour (with a biopsy)
  • Assessment of the regional lymph Nodes (the ‘glands’ such as we have in our necks)
  • Assessment of other sites for Metastasis (spread elsewhere)

Staging is generally performed by a combination of physical examination, diagnostic imaging and biopsy samples of the tumour (‘cytology’ or ‘histology’). In some cases, the appearance on diagnostic imaging may be sufficient to make a diagnosis without biopsy, e.g. nodules in the lungs seen on an X-ray of the chest suggests spread of cancer cells to the lungs.

This clinical staging represents the ‘gold standard’. However, this approach is not necessary or appropriate in all cases. For instance, for a pet with a benign tumour confirmed with a biopsy taken by sucking cells out of the tumour through a hypodermic needle (needle biopsy), the outlook is excellent and the likelihood of tumour spread is very low, so staging may be taken no further after gaining some information about the primary tumour.


Care of Pets with Cancer

We all may have our own view of how a tumour is affecting a pet and owners may well have other concerns about their pet. The supportive care of the patient is the second part of compassionate patient care, after ‘diagnosis’ and before ‘therapy’. This is important, as we wish to avoid the tendency to leap from diagnosis to treatment without considering what supportive care is needed. Our approach to supportive care can be summarised by three important rules:

  1. Ensuring patients do not experience pain or discomfort associated with the tumour or its treatment
  2. Ensuring patients are able to eat a normal amount of food to meet their nutritional requirements, and if they cannot, we should think about how to help them to do so
  3. Ensuring patients do not suffer side effects of the tumour or therapy, such as vomiting or feeling sick when undergoing treatment, if at all possible.

Management of Chronic Cancer Pain

When asked what our concerns about cancer would be, most of us would say that pain associated with cancer would be uppermost in our minds. As a rule, we understand how to manage acute pain after an operation, however the management of chronic cancer pain in a patient where a total cure is not possible is sometimes more difficult to achieve.

We have detailed methods of assessment of pain and discomfort and understand the importance of treating and managing pain or discomfort associated with cancer. It is important to realise that management of pain does not just involve drugs traditionally thought of as ‘painkillers’ but may also include other drugs that have an effect on the way nerves and the brain deal with pain (e.g. gabapentin and amitryptiline) or drugs and other therapies that have an effect on the tumour itself (e.g. bisphosphonates or radiotherapy in cases of the bone tumour, osteosarcoma).

In some tumours the most successful method of pain relief may be surgical removal of the tumour itself, whether that is a procedure designed to cure the patient or a treatment designed to remove or reduce the clinical signs associated with the presence of the tumour without totally curing it.


Tumour Biology

As a general rule, if the basic biology (behaviour of the cancer cells) of a disease cannot be understood it is not possible to provide appropriate treatment. One important lesson that has emerged from both human and veterinary oncology is that, when it comes to cancer, the biology of the disease will dictate what happens in the long-term.

A common question asked when a diagnosis of cancer is made in a pet is ‘What caused the cancer?’ While we know something about some causes (and what is happening in the cancer cells and their genes), for the most part, we do not know the cause.

The total number of cells in a person or animal is a balance between the number of cells growing and those dying. For a long time it has been considered that cancer is a disease caused by uncontrolled cell growth. However, of more importance is the fact that cancer cells refuse to die when programmed to do so. Cancer therapies that encourage cell death are likely to be just as important as, if not more important, than therapies that prevent cell growth.

Other examples of cutting edge treatments in humans that have been developed as a result of understanding tumour cell biology include those designed to stop the early phase of tumour spread (metastasis) by preventing tumour cells moving through the tissue, and those causing a reduction in tumour growth by preventing the tumour causing the growth of new blood vessels (angiogenesis) which the tumour needs in order to grow.


Tumour Pathology

Pathologists play a critical role in the investigation of patients with cancer by examining tissue from the primary tumour and, in some cases, the lymph nodes and other potential sites for spread.

Assessment of cells obtained from a mass with a hypodermic needle (cytology) is often the first approach in the diagnosis however in most animals, examination of a tissue sample (histology) is necessary at some point during the assessment of the patient.

Histological assessment of the tumour may also provide more specific information regarding the outlook:

  • Examination of the tumour edges after the growth has been surgically removed may indicate if the tumour is likely to grow back in the same place (i.e. if there are tumour cells at the edge of the specimen, it is likely that tumour cells have been left in the patient)
  • Examination of a large specimen for evidence of tumour cells spreading into the blood vessels or lymph drainage vessels may suggest whether the tumour is likely to spread.

Other Effects of the Tumour (Paraneoplastic syndromes)

Paraneoplastic syndromes are additional effects that cancer might have in parts of the body away from the original tumour. These abnormalities may have an effect on a patient’s health and may impact their ability to tolerate sedation or anaesthesia and treatment. The paraneoplastic syndrome may be the initial reason for the animal being taken to the Vet (the owner may not even realise that there is a tumour somewhere) and these syndromes may also provide a useful guide to the success of therapy, i.e. if the paraneoplastic syndrome gets better, this suggests that the tumour tissue has been removed or destroyed. In rare cases, the paraneoplastic syndrome may be very obvious but the location of the underlying primary tumour is more difficult to find. In such cases, additional imaging procedures can prove very helpful.

Examples of these syndromes are alterations in the number of red blood cells or white blood cells in the circulation and abnormalities in the blood level of glucose or certain salts or ‘electrolytes’ (e.g. calcium).


Achieving a diagnosis

As a general rule, a biopsy (taking cells or a larger piece of the tumour for analysis) is needed before beginning any therapy. A biopsy may be omitted if knowing more about the tumour would not change the treatment plan or the willingness to treat the patient. However, care is taken to ensure that these reasons apply in any individual patient. A biopsy should always be tailored to the individual tumour and we will always consider whether a biopsy of the regional lymph node (gland) or other sites of potential metastasis (spread) is needed at the same time.


Selecting the Best Cancer Treatment

Once a diagnosis has been achieved and there is information on clinical staging, the effect of the tumour on the patient and any coexisting diseases, and once it has been identified if the patient needs additional supportive care, different treatment options can be considered.

The main treatment options for the management of cancer are:

  • Surgery: The physical removal of the tumour
  • Radiotherapy: The use of a strong X-ray beam to destroy the cancer cells where they sit
  • Chemotherapy: The use of anti-cancer drugs to kill cancer cells wherever they are.

    Each of these has specific advantages and disadvantages and may be used singly or in combination. All of the factors listed above, particularly the tumour type, grade, stage and location and the presence of other health problems will help to decide what the most appropriate therapy is. Therapy may be designed to cure the patient or to remove the signs of illness for as long as possible, if a complete cure is not possible.

In addition, other ways of treating cancers are becoming more common in human oncology, and these benefits will become available for animals in due course, including:

  • Immunotherapy; vaccination with melanoma-specific antigens in patients with melanoma (a tumour of the pigment cells in the body)
  • Targeted therapy with small molecule inhibitors; tyrosine kinase inhibitors (TKIs) which may be used in some patients with mast cell tumours.

Monitoring Response to Therapy

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