Murdoch University Veterinary Hospital

Breast Cancer in Dogs and Cats

Breast cancer, usually mammary carcinoma, is a relatively common disease in dogs and cats that have not been desexed before 2 years of age. Animals desexed at or before 6 months of age have the lowest risks. Around 5 out of every 6 breast growths in cats and half in dogs, are malignant. This means that they are showing changes under the microscope which indicate the potential for the cancer to spread elsewhere in the body, and therefore to be fatal. Because these changes are only visible in relatively large sections of tissue removed from the lump, the first step that must be taken is removal of the lump itself. If the laboratory that analyses the tissue reports that the mass is a malignant cancer, then several things can be done. Sometimes more aggressive surgery may be necessary. Secondly, it is worth taking some x-rays of the lungs to see if the cancer is advanced. Note that if the x-rays do not show the tumour, it only means that the cancer is not advanced but small secondary growths may be present. (It takes around 500 million cancer cells to show up on an x-ray.) If the report from the laboratory shows specific changes that mean the tumour has very likely spread (or metastasised) then we assume that it has done so. Most dogs and cats with cancers in this category do not live more than 3-6 months without further treatment. Medical treatment has been shown to have the potential to dramatically reduce the numbers of cancer cells elsewhere in the body, meaning that the patients retain normal quality of life for significantly longer periods of time. The majority of patients do not have any side effects limiting their quality of life whilst they are receiving treatment. Treatment is not necessary for every patient, and can be costly. By the completion of treatment (usually 3 months), most people will have spent over $1000. Whilst this type of treatment may not be for everybody, the Murdoch Animal Cancer Care Unit can also advise on other aspects of cancer including nutritional intervention and pain assessment and control. Simple treatments are also available to help slow the cancer’s growth.

Tumours of the Male Reproductive Tract

 Testicular cancer

Fortunately, testicular cancer in dogs is usually much less aggressive than in man. For the majority of dogs, surgical removal of the tumour is curative. Whilst many people are uncomfortable with the idea of castrating a pet, we all have a duty to safeguard our pet’s health, and castration is kinder than cancer. In general, this surgery will not change your dog’s behaviour other than reducing dominance aggression (but not territorial or protective aggression). Castrated dogs only put on weight if overfed. In most instances, referral is not required; your own veterinarian is the best person to perform this procedure.

In some instances, these tumours can spread elsewhere. Evidence of lymph node enlargement, or the results from the laboratory that examine the tumour after surgery may suggest that more than surgery is necessary. In this case, your veterinarian will advise you come to the Murdoch Animal Cancer Care Unit to discuss treatment of the cancer. Medication can do a lot to keep your dog comfortable and generally doesn’t cause any illness itself.

Some testicular cancers can produce the female hormone, oestrogen. This produces skin changes and hair loss, but can also cause serious damage to the bone marrow that may be irreversible. A blood test will detect the marrow injury rapidly.

Prostate cancer

Prostate cancer is the most common reason for a castrated dog to have a large prostate. Castration does not prevent prostate cancer in dogs, and does not slow it down once it has developed. Prostate cancer in dogs can respond very well to cancer drugs. The result is not cure, but often a dog with normal quality of life for another year or two. Surgery can sometimes help but will cause urinary incontinence; any benefits are for the short term as the cancer has usually spread before detection. There are several ways that many of the symptoms of prostate cancer in dogs can be eased with various medications. Often it may be possible to have a consultation at the Murdoch Animal Cancer Care Unit initially, followed by check ups with your usual veterinarian.

Tumours of the Female Reproductive Tract

Ovarian Tumours:

These are uncommon in dogs and cats. Most of the tumours that occur in both species are cancerous and have spread by the time of diagnosis to other parts of the abdomen, as well as the lungs. Most of the time, the first symptom will be an enlarging abdomen. Sometimes, the tumours produce the female hormone oestrogen, which leads to enlargement of the vulva, persistent signs of being on heat, hair loss, or pale gums. If your veterinarian suspects the presence of an ovarian tumour, surgery will be necessary to be certain, and also to remove the tumour. Ultrasound examination may help beforehand to obtain more information about the mass. Surgery can be curative, and is therefore strongly advised. However, for many pets, evidence obtained by ultrasound, at surgery, or from the laboratory report following examination of the tumour, indicates that the tumour has spread elsewhere in the body. In this instance, medication can be very successful in markedly delaying recurrence of the disease, or possibly eradicating it. Your veterinarian will advise referral to the Murdoch Animal Cancer Care Unit in this instance.

Uterine Tumours:

 Fortunately for most dogs with this rare tumour, the problem is benign and cured by surgery. For cats however, the tumours are typically advanced at diagnosis, and have spread. The most common symptom in both species is the presence of a vaginal discharge. Surgery is required in all cases. For some, medication will be required afterwards, given at the Murdoch Animal Cancer Care Unit so that quality of life can be maintained for a longer period.

Vaginal Tumours:

 These tumours can grow to be very large, but fortunately are mostly benign. Surgery therefore is typically successful in curing the patient. Occasionally, cancerous tumours will appear in this location. Your veterinarian may suggest referral in this instance.

Soft tissue sarcomas are a group of tumours that grow from connective tissues in the body. Often they don’t spread elsewhere but can be a problem due to invading very deeply. High-grade tumours can spread through the body, and the risk of this happening is best determined by submitting a piece of the tumour to the laboratory. If the risk is low, there are 3 types of treatment available for your pet:

1. The most effective treatment is surgery, however this must be aggressive to have any chance of cure. In many cases this may mean removal of nearby structures, and for limb tumours, amputation may be required. It is not an easy decision to make, but most pets are better off if the cancer can be completely removed.
2. Minor surgery can be done to remove all, or most of the visible tumour. Recurrence will occur, and this procedure is only useful if the tumour has been growing very slowly. Please note that if this procedure is performed, it may lessen the success of more aggressive surgery if you change your mind at a later date.
3. Injections of chemotherapy into the tumour. The advantage of this technique is that very high concentrations of drug are placed into the tumour, while very little diffuses out into the patient. Chemotherapy side effects therefore do not occur. Success rates are lower than with surgery, hence this technique is best reserved for:
   1. An attempt to control the tumour first without surgery, if waiting several weeks to determine response doesn’t interfere with the surgery that may still become necessary.
   2. Pets for whom you feel surgery is not appropriate.

If the tumour is classed as high grade, the potential for spread becomes very high. In this instance it is preferable to follow removal of the tumour with medical treatment aimed at removing remaining cancer cells. This should result in your pet having a significantly longer period of normal quality life. These medications generally will not make your pet ill.

In most cases surgery will be done by your veterinarian, however there will be some procedures for which they may prefer that your pet is referred to a specialist. You will need to be referred for injections of chemotherapy or for the medical treatment of high-grade tumours.

Squamous Cell Carcinoma 

Squamous cell carcinoma is a common cancer of the skin and mouth in dogs and cats. The skin form is typically the result, as in people, of excessive sun exposure, but not necessarily sunburn. Skin cancer is often best frozen or surgically removed, and your veterinarian is typically the best person to do this, without the need for referral to a specialist. However, in some situations, the equipment required for achieving more depth for freezing, or the particular surgery required will require referral to the Murdoch Animal Cancer Care Unit.

When the cancer occurs in the mouth, it is not the result of sunlight exposure – the cause is unknown, though has been associated with owners that smoke for cats. In cats, the disease is particularly aggressive and generally not curable. Surgery can be done, but must be aggressive. Alternatively, local injections of chemotherapy can often control the disease, and do not cause ‘chemotherapy’ side effects. For dogs, the prognosis can be better, and for some, cure is a likely outcome. Treatment options are the same as for cats.

Your veterinarian will advise you on how best to commence diagnosing and treating your pet’s tumour. At some point, a specialist opinion may be helpful to offer advice, or to commence some of the therapies listed above. Your veterinarian can organise referral to the Murdoch Animal Cancer Care Unit, at Murdoch University. Costs can range from $110 for the consultation only, up to $1000 or more for some of the medications used and surgeries required. At the time of consultation, you will be given as much information as possible on how effective any treatments are likely to be for your particular pet, how much cost will likely be involved, and whether any reactions to the particular treatments are possible.

Carcinoma

Carcinomas are cancers that originate in tissues that line the inside or outside of organs, such as the skin, lungs and intestine, or from glandular tissues such as the breast. They vary in how aggressively they behave; for some, surgical removal is curative, whilst for others metastatic spread through the body occurs long before the first ‘lump’ is detectable. In order to estimate the behaviour of a cancer, we use information from your description of its appearance and growth, its location, and importantly, the tumour’s appearance under the microscope. This last step means that a biopsy is generally necessary to advise you fully, although there are selected situations where this can be avoided. The biopsy can be taken with a minimally invasive instrument, through to removing a large piece, or if cure is likely, the whole mass. Your veterinarian generally best makes the decision on which process is most appropriate, though on occasion referral to a specialist may be desirable. 

Treatment generally is surgical and/or using medication. Medication can be anything from tablets at home, through to injections of chemotherapy, which generally do not cause any side effects in cats and dogs. The aim of medical treatment can be to improve quality of life by reducing the amount of cancer present, through to preventing further growth of the cancer, and finally palliative treatments are often available that focus on the patient rather than the cancer. The decision regarding which of these therapies best suits your pet is generally best made after compiling all the information available, following referral to Murdoch University. Remember that the aim of treating any cancer in pets is based on achieving quality of life above all else.

Mast cell tumours in dogs

 Mast cell tumours are the most common cancers of the skin and underlying (subcutaneous) tissue in dogs, despite being quite rare in people. Whilst the genetic abnormalities that occur within the cancer are well characterised, the causes are unknown. Breeds such as Boxers and Staffordshire bull terriers are at much higher risk than other dogs. Almost all of these cancers begin in or under the skin, but rarely can originate in the stomach or intestine. The tumours themselves generally appear as a lump in the skin, and may appear reddened or ulcerated. The tumours vary greatly in their degree of malignancy; some will never be more than a small lump in the skin whilst others will grow rapidly and spread elsewhere in the body.

 Initially, a diagnosis must be made. At some point, a sample of tissue will need to be sent to the laboratory to determine how aggressive the tumour is. Generally, the cancer will be given a grade, where grade I tumours are low grade and generally harmless, and grade III tumours are high grade and spread rapidly. All of them however tend to burrow deeply into the surrounding tissue such that the visible mass is no more than the ‘tip of the iceberg’. The surgeon therefore will take as much tissue as possible around the cancer to decrease the odds of leaving any microscopic cancer behind. Often, only surgery will be necessary to effect a cure. For tumours of grade II or III severity, and especially if the location prevents aggressive surgery from being performed (e.g. the leg or face), medications are available that can make a dramatic difference to the future of these dogs. The majority of dogs with mast cell tumours that need medical therapy will be cured. Furthermore, 95% of the time, there are no side effects. Serious side effects occur 1% of the time.

 The treatment itself is usually intravenous injections, which are quick and largely painless. Most dogs will receive 8 treatments over 12 to 16 weeks. Costs can be significant, with each treatment visit being around $260.

 Although the main medication is a natural extract (of the Jamaican periwinkle plant), it is not safe to handle as a ‘normal’ drug. Murdoch University is equipped to allow the safe use of this extract, and your veterinarian is able to organise referral for you.

Canine Osteosarcoma

Osteosarcoma is the most common bone cancer in dogs. It most often occurs in a front leg away from the elbow, or a back leg close to the knee. It can also occur in bones of the spine or the skull. Because this is a serious disease that is rapidly fatal without correct treatment, your veterinarian will want to get a certain diagnosis very quickly. This can be done by taking a biopsy, and having a laboratory examine the sample. In some cases, the lesion is so aggressive and painful that limb amputation may be necessary immediately – the sample is then taken at the time of surgery and submitted. Although the surgery required to remove an osteosarcoma is aggressive, you must realise that this is the most effective form of pain control for the condition. Most dogs do very well after surgery, and are typically more comfortable within a few days of surgery than they were before. Dogs generally will not show symptoms of chronic pain – by the time it is severe enough to notice, for example by decreased appetite, the dog has suffered enormous discomfort. 

Chest x-rays are often taken prior to surgery. If the tumour can be seen in the chest (about a 10% chance), the prognosis is very poor, and it may be kinder to consider euthanasia rather than treatment. If there is no tumour visible in the chest, this means that the cancer is not advanced (but will almost certainly be hiding there) and that cancer treatment is likely to be worthwhile. Unfortunately, if surgery is the only treatment given, most dogs will not live more than 3 or 4 months although the source of pain will have been removed. With cancer therapy in addition to surgery, about half of dogs will live 16 months or more, and about 1 in 4 or 5 will be cured. Cancer therapy therefore obtains good control of the disease and in most dogs causes no side effects: 70% of the time our treatments have no side effects at all, and another 25% produce only brief, mild problems. Only one dog in 20 will have a serious reaction to the medication, which is almost always successfully and rapidly controlled.

 Because of the nature of the drugs used to treat osteosarcoma, you will need to be referred to the Murdoch Animal Cancer Care Unit at Murdoch University. This is a state-of-the-art unit that meets not only veterinary, but also human hospital requirements. The unit is co-ordinated by Dr Ken Wyatt, who is a registered specialist and works solely in the field of animal cancers. In many cases, your veterinarian will be the best person to do the initial surgery. Alternatively, there are surgical specialists for whom your veterinarian can arrange referral. 

Costs can be very high with this sort of treatment. Surgery may cost from $500 to several thousand dollars, and medical cancer treatments can cost the same again. The cancer therapy is given via a drip, every 3 weeks on up to 6 occasions, and does not require overnight hospitalisation. It is important to remember that all the treatment for this disease is designed to restore quality of life, and to then provide as much time as possible. Veterinarians do not wish to extend your pet’s life for anyone’s benefit other than that of your pet. If you would like to consider treating your dog for this condition, appointments for the Cancer Unit can be made on 1300 652 494.   

Lymphoma is the most common cancer formed from blood cells that occurs in dogs and cats. However, the chance of any one dog developing this disease over any one-year period is less than 1 in 1000. This disease is similar to non-Hodgkin’s lymphoma in people, and has been called lymphosarcoma and malignant lymphoma. The different names don’t indicate any difference in the condition. Lymphocytes are the type of white blood cells that produce antibodies (B cells) and help to fight against viruses and cancers (T cells). Most lymphomas are due to cancerous B cells. Because the natural behaviour of lymphocytes is to circulate around the body, the same behaviour continues once they become cancerous. They are typically systemic, or body-wide, regardless of where the disease is detectable. For most, the cause of the disease is unknown, although there is a connection in dogs to heavy exposure to paints and solvents. In cats, sharing a house with smokers can increase the risk as does FIV (the feline “AIDS” virus) and Feline Leukaemia Virus. Dog breeds such as the boxer and golden retriever appear to be at increased risk. There has been a line of bullmastiffs reported with an extremely high risk of lymphoma. The exact reasons for these predispositions are unknown. 

The disease is rapidly fatal. Most dogs succumb within 2 months of diagnosis if treatment is not initiated promptly. This is an average figure – some dogs will have less aggressive forms and live for 6 or 7 months, whilst some will decline within days. Most dogs develop the high-grade (aggressive and rapid) form. Treatment can be either palliative or can aim to reduce the cancer burden directly. Palliative therapy is generally corticosteroid (“cortisone”) tablets, which can produce a dramatic short-term benefit in about half of all patients. Length of life is not improved, but quality of life is often much better. The only therapy proven to be very effective in pets is medical therapy. Drugs are used to kill large numbers of cancer cells (well over 99%), which places the patient into remission. Remission means that the tumour cannot be detected, and is unable to cause any symptoms. Hence your pet will have normal quality of life. For the majority of patients there exists a therapeutic “window” such that medication can result in complete remission for good periods of time, with ZERO side effects. With all treatments, there exists a risk, and around 1 in 20 patients will have serious reactions to the medication. 

The patients that do best with treatment tend to have B cell lymphoma (this factor only applies to dogs), are not showing signs of obvious illness at the time of diagnosis, and do not have the beginning of treatment delayed. For most, the age of the patient, or how advanced the disease is at diagnosis does not seem to alter success greatly. 

Treatment can be given in many different ways. The most effective therapy uses many different drugs in rotation, with the aim of delaying the development of resistance within the cancer. Around 85% of dogs that receive treatment go into remission, and typically within days or weeks. Dogs receiving therapy have a 50% chance of still being alive 15 months after treatment first started and around a 15% chance of cure. For cats, around 2 out of 3 go well initially, with 1 out of 3 likely cured. The drugs are used in such a way that quality of life is more important than length of life. This lowers the cure rate, but means that however long they live, they enjoy that period of time. Treatment is generally given for 6 months. Other treatments are available that are simpler, and these may only require as little as 5 treatments over 15 weeks. The longer-term success with these shorter treatments is not as good, however. As with many advanced treatments, the costs can be high. Most people having their pets treated for lymphoma will spend from $500 to many thousands of dollars.

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Haemangiosarcoma

Haemangiosarcoma is a cancer that forms from blood vessels. It most commonly forms in the skin, or internal organs such as the spleen or heart. In both dogs and cats, the internal form is very serious. Without treatment, most patients have a life span of days to weeks. The skin form can be aggressive in some cases, and the laboratory results will determine this. There are 3 successful forms of treatment available at present to fight this disease. The first is surgery. If possible, all visible disease needs to be removed. If this involves removal of a benign (or unable to spread) skin haemangiosarcoma, then surgery alone can be curative. For all other forms in dogs and cats, tumour spread elsewhere is expected even though it usually will not be visible or detectable immediately.

 The other 2 forms of treatment involve the use of medications. For patients that have had all visible tumour removed, medical treatment is available that results in significantly longer periods of normal quality of life following surgery. Whilst not every patient responds, there is a 50% chance of living another 6 to 12 months or longer, and a 10% chance of cure. The treatment is given in such a way that side effects are uncommon. Treatments are generally given on 5 occasions, 3 weeks apart and require that your pet be in hospital at Murdoch University for as little as a few hours. Costs can be high, with medical cancer therapy treatments costing from several hundred dollars per treatment.

 If the spread of tumour is advanced (in other words, visible) then standard treatment can still be used but is often not as successful. Alternatively, there is treatment available that can prevent blood vessel growth leading to a halting of tumour growth overall. Treatments aimed at preventing blood vessel growth are given at home, and require visits fortnightly initially, but less often later. Treatment costs between $100 and $200 per month for this form of therapy.

Melanoma

Melanomas are relatively common tumours in dogs, but rare in cats. In both species they can range in behaviour from benign (harmless) to malignant (potentially fatal). For many animals with a melanoma of the skin, surgical removal is curative. The most accurate way to predict the behaviour of a skin tumour is to have a sample sent to the laboratory. Melanomas in locations other than the skin, such as inside the mouth in dogs, or in the eyes of cats are generally more aggressive than the skin form.

There are many ways we treat patients with melanoma:

1. Surgery. This is the best first-line therapy, and is usually successful in preventing the tumour growing back at the same site. Unfortunately, there are no tests available that detect the tumour elsewhere until the disease is very advanced. In general, if the tumour appears malignant at the laboratory, it usually has already spread elsewhere in the body, and most often to the lungs, even though it may not be visible on x-rays for some time.
2. Intralesional chemotherapy. Injecting chemotherapy drugs into the tumour removes the tumour completely from its original site in about half of all cases. The doses used are too small to cause any side effects, and are generally done under sedation. Most commonly, 4 treatments are given, each a week apart.
3. Systemic chemotherapy. This form of chemotherapy is used to treat the whole body and hence fight cancer wherever it has spread to. The way in which this is done in animals results in no serious side effects in 95% of patients. On average, treatment lasts 2 months and has been shown in dogs to triple their remaining time.
4. Anti-blood vessel treatment. In patients with very advanced disease but good quality of life, treatment against the blood vessels is more effective than fighting the cancer itself. Successful treatment limits further growth of the tumour.
5. Nutritional changes and pain control. There are several changes that can be tailored to individual patient’s diets to improve quality of life. Pain control can be helpful in animals with advanced disease even if they do not show obvious signs of pain.

Your veterinarian will advise you on how best to commence diagnosing and treating your pet’s cancer. At some point, a specialist opinion may be helpful to offer advice, or to commence some of the therapies listed above. Your veterinarian can organise referral to the Murdoch Animal Cancer Care Unit, at Murdoch University. Costs can range from $110 for the consultation only, through to several hundreds of dollars for anti-blood vessel treatments, up to around $1000 for intralesional chemotherapy or possibly more for systemic chemotherapy. At the time of consultation, you will be given as much information as possible on how effective any treatments are likely to be for your particular pet, how much cost will likely be involved, and whether any reactions to the particular treatments are expected.