ACT::Animal Cancer Trust

Types of cancer Benign or malignant? PDF Mast Cell Tumours PDF Mammary Tumours - dogs PDF Canine Lymphoma PDF Canine Haemangiosarcoma PDF Skin Tumours PDF Mammary Tumours - cats PDF Bone Cancer - dogs PDF Basal cell carcinoma of gum	Types of Cancer There are many types of cancer and they vary in how they affect the patient, how they can be treated and the outcome of treatment. The aim of this part of the site is to provide basic information about the tumour types and their treatment. However, it must be stressed that these are general statements and it is important to discuss the various aspects with your vet. BENIGN OR MALIGNANT? A tumour is a ball of cells that is growing outside the strict limits of control that the body normally imposes. Tumours are also referred to as neoplasms or neoplastic growths. Tumours are essentially normal cells that have gone wrong. The cell of origin determines the type of tumour that develops. Tumours may be benign or malignant. Malignant tumours Malignant tumours are potentially the most dangerous type of tumour – they are otherwise known as cancer. They grow by invasion into the surrounding tissue. The direct effects of this vary according to which part of the body is involved. In the skin, the tumour may become ulcerated, inflamed and painful. If the tumour involves bone this may become weakened and indeed may fracture. Tumours that involve bone are frequently painful. The other major characteristic of a malignant tumour is that it has the ability to spread to other parts of the body. This process is known as metastatic spread (metastasise) and the new tumours are called metastases or secondaries. These secondaries can occur anywhere in the body but the common sites are the lymph glands and the lungs. They can also spread to the liver, kidney, brain and bones. However, not all malignant tumours undergo secondary spread. Some cancers, often referred to as low grade, have a low metastatic rate - that is to say only a small percentage actually spread. Tumours arising from fibrous tissue in the skin of dogs (known as fibrosarcoma) are generally low grade and less than 15 per cent metastasise; however it is often not possible to say which will be the dangerous one. At the other extreme there are cancers with a high metastatic rate where most will spread. Bone cancers in dogs (osteosarcoma) are ‘high grade’ and at least 95 per cent will metastasise. Predicting which patient will develop secondaries is often impossible unless they are at a size that can be seen on a radiograph or by ultrasound scan. However, if no secondaries are seen on the chest x-ray that is no guarantee that secondaries will not develop at a later date. A secondary tumour starts as a small ball of cells less than 100th of a millimetre and it must grow to a size where it can be detected. To be visible on an X-ray the mass has to be about almost 1 centimetre diameter. The rate of growth to get to this size can be slow for some tumours or rapid for others. Most secondaries break away and grow when the original primary tumour is tiny. Secondaries that appear after a primary tumour has been removed will have been present but not detected at that time. For tumours with a high likelihood of secondary spread, anticancer drugs (chemotherapy) may be recommended to delay or even prevent secondaries; however, not all tumours are sensitive to drugs. Metastatic spread is the most difficult type of cancer to treat and, as they grow, they take over more of the patient’s normal organs until the patient dies. Secondaries growing in the lung, for example, will reduce the function of the lungs such that the patient cannot get enough oxygen and tires easily. As the tumours grow further coughing and general illness may also become apparent.

Mast cell tumour on nose	MAST CELL TUMOURS IN DOGS Mast cell tumours are one of the commonest skin tumours seen in dogs. There is great variation in what mast cell tumours look like and how they will behave. Their behaviour varies from almost benign, slow growing, low-grade tumours at the one end of the scale to very aggressive, high-grade cancers at the other end. Mast cell tumours at the least aggressive end of the scale are, for the main, potentially curable whereas the aggressive ones are frequently fatal. In order to get an idea of a likely prognosis and to give the most appropriate treatment, we need to know which end of the spectrum we are dealing with. Assessment of degree of malignancy The best way of assessing how the tumour will behave is to have it examined by a pathologist. The pathologist uses a grading system based on the microscopic appearance and this actually correlates quite well with the clinical behaviour at the two extremes of the spectrum. The three grades are a) well-differentiated, b) intermediate differentiation and c) poorly differentiated. The term “well differentiated” correlates with the least aggressive form. Less than 5% of these ever spread anywhere else in the body and the vast majority are curable by surgery, radiotherapy or a combination. What the pathologist call “poorly differentiated” tumours are the very aggressive forms. At least 80% of dogs will develop secondaries elsewhere and the majority of patients will die as a result of the tumour at some time. Treatment is aimed at delaying the onset of the advanced state but cures are uncommon. Unfortunately there is a large number that the pathologist is not able to categorise and will call “intermediate grade”. Most of these are actually not very aggressive and only 15-20% will undergo spread elsewhere. Put another way, 80-85% are potentially curable. Treatment options The first aim of cancer treatment is to control the primary tumour, remove it and prevent local recurrence. The second aim is to reduce the rate at which secondary tumours develop. As a rule, surgery has the best chance of curing any tumour; for some tumours, local excision is curative but for others a very wide margin beyond the apparent mass is required to deal with any infiltrating fingers. For mast cell tumours, relatively local surgery can be curative for the well-differentiated (least aggressive); whereas the intermediate differentiation have widely infiltrating fingers that require bigger surgery. Where wide surgery is not feasible (e.g. lower limb or skin of face), there will be a high chance of recurrence with intermediate grade mast cell tumours (at least 50%). However, if radiotherapy is used after surgery it is possible to cure many more

	MAMMARY TUMOURS IN DOGS Mammary tumours are common in middle aged and older entire bitches. Although the majority of mammary tumours are benign, a significant number are malignant and potentially life threatening. What causes mammary tumours? Mammary tumours occur in mammary glands that have been exposed to female hormones. They are very rare in male dogs and in bitches spayed (ovario-hysterectomy) before their first heat. In Britain spaying before the first heat is uncommon but so long as this operation is performed before the second heat the number of bitches that develop mammary tumours is still very low. Mammary tumours in bitches are almost preventable. In general, any bitch that is not going to be used for breeding is best spayed before its second heat to prevent mammary cancer and diseases of the uterus. How could mammary tumours affect my dog? Whether they are benign or malignant, tumours of the mammary glands will grow and may become ulcerated, infected and painful. Benign tumours tend to grow slowly whereas mammary cancers tend to be more aggressive. However, growth rate and what they look like are not always good indicators of actual type and behaviour. Mammary tumours can occur as single lumps, several at one time or over a period of time. Benign tumours are more frequently multiple BUT this is not a guarantee that one of the lumps is not malignant. Malignant mammary tumours are potentially life threatening. Not only can they grow quickly and become ulcerated, but around 50 per cent will undergo secondary spread to other parts of the body. These secondaries are very difficult to treat and will continue to grow until they are causing major problems and ultimately will be fatal. If a lump starts growing in the mammary gland then it is always best to ask your vet to look at it before it grows further. Small tumours are easier to treat and potentially more curable than large ulcerating masses. What treatments are there? Surgical removal of the tumour when it is small (less than 2 centimetres) has the best chance of curing the patient. Usually a biopsy is not required but if your veterinary surgeon is concerned this may be performed first. If there are multiple lumps then several incisions may be required or one larger area. Malignant tumours will grow into the surrounding tissue. So long as some of the normal tissue is removed with the tumour there is a good chance that a local cure can be achieved. However, surgery will not reverse secondary spread if it has occurred. The longer a malignant tumour is left, the bigger it will grow and the greater the chance of secondary spread occurring. Currently there is no effective treatment against secondary mammary cancer. Anticancer drugs (chemotherapy) and hormone antagonists (e.g. tamoxifen) are frequently used in women with breast cancer with good effect; however these drugs do not appear to be very effective in bitches. If my bitch has a mammary cancer what is the prognosis? In general, so long as the mammary tumour is removed when it is small, the prognosis is good for the majority of bitches. Larger tumours, especially if they are malignant, are much more problematic and there is an increased chance that fatal secondaries will develop.

	CANINE LYMPHOMA Canine lymphoma (lymphosarcoma) is a cancer arising predominantly in the lymph glands of the body. In some dogs, this may occur at only one or two sites in the body but, more commonly, it is widespread involving all the lymph glands and internal organs. Lymphoma is a progressive and ultimately fatal disease unless treated. In the early stages, the patient may be well but the cancer can have a profound effect on the dog causing weakness, poor appetite, loss of weight and general poor health. Currently, the cause of canine lymphoma is not known. However, it is not a contagious disease and there is no chance of spread to other pets or to humans. Without treatment, the average survival time is about 4-6 weeks. In some rare cases it may take several months to progress. With treatment, the majority of patients will go into remission (i.e. the tumour is reduced to such a small size that it is no longer apparent). This remission can be long lasting but unfortunately, lymphoma is rarely cured outright. Treatment possibilities vary from basic drugs to complicated protocols using a variety of drugs. The principal and most important goal of any treatment is to regain and maintain a good quality of life. For the majority of dogs the drugs that are used have minimal to no side effects. Steroids alone will achieve a partial response in many dogs but they will relapse within 2 - 3 months due to drug resistance. For a longer and more complete response, combination drug therapy is used. Using a basic three-drug protocol of cyclophosphamide, vincristine and prednisolone a good response can be achieved in three-quarters of cases with an average survival of 7 - 9 months (a small percentage reach 2 years) and relatively few side effects. More advanced multi-drug protocols that include doxorubicin exist. They can achieve a better remission rate with a longer average survival of 12-14 months with some dogs reaching two years. However, these regimens are more involved, can have more side effects and tend to be more expensive. Side effects from the anticancer drugs are not common; in general, the quality of life for most veterinary patients receiving cancer treatment is good and often normal. Many dogs that were ill because of the lymphoma will actually improve dramatically as their tumour comes under control. While it is important to be aware of the potential side effects of chemotherapy, the majority of our patients complete their treatment without significant complications. Most of the time they can lead full happy lives and have fun with the families that love and care for them. The first aim of therapy is always quality of life and, second to that, for a ‘worthwhile’ period. Your vet may want to refer you to a cancer specialist for more advanced treatments and, indeed, you can ask to be referred.

	CANINE HAEMANGIOSARCOMA Haemangiosarcoma is a malignant tumour that arises from the cells that line blood vessels. The most common sites for this tumour include the spleen and the right atrium of the heart but can also arise in the subcutaneous tissue. German shepherd dogs appear to be at risk of developing this type of tumour in their spleen or heart. Dogs often collapse following an acute bleed due to rupture of a splenic tumour. This rupture will spread malignant cells around the abdomen. On occasions the splenic mass is found before it ruptures. Surgery is the treatment of choice for the primary tumour. Unfortunately, haemangiosarcoma tends to be a very malignant tumour and most individuals will die from metastatic disease throughout the body. The average survival following surgery alone is less than 3½ months with very few dogs living beyond a year. The addition of anticancer drugs (principally doxorubicin-based protocols) can improve the survival times. However, 50 per cent of all dogs still die within 7 months. Dogs that have had surgery for an intact splenic mass and where no metastases were detected achieve a slightly better than average survival of 8 months and about a quarter live beyond one year. Dogs in whom the splenic tumour had ruptured tend to do less well (average 6 months) following surgery and anticancer drugs. The anticancer drug regimen is generally well tolerated but does have potential side effects. These include varying degrees of lethargy, anorexia, vomiting, diarrhoea, and fever. Mild to moderately low white blood counts (neutropenia) occur in up to half of dog cases but usually do not require treatment; however about 10% of dogs can develop severe neutropenia and fever requiring hospitalisation. Severe neutropenia is potentially fatal and even with supportive treatment dogs can die from this.

Squamous cell carcinoma (probably due to overexposure to strong sunlight)	SKIN TUMOURS IN DOGS AND CATS The skin is the most common site to be affected by a tumour in dogs and the second in cats. Skin is a complex structure with several different cell types and as a result a number of different tumours can develop. In fact some 25 different tumours have been identified although some are quite rare. In dogs, the majority of skin tumours are benign whereas in cats the majority are malignant. Benign skin tumours are usually slow growing, well defined and mobile over underlying structures. Malignant tumours tend to grow faster, infiltrate into adjacent tissue and may become red, inflamed and ulcerated. However, the physical appearance of the tumour is not always a guide to how it will behave. Needle samples for cytology or a surgical biopsy for histology may be necessary to identify the tumour type more accurately. The type of tumour determines how it is likely to behave and what the best course of treatment should be. Many of the skin tumours in dogs are benign and will never be a life-threatening problem. Whilst most benign tumours are easily cured by simple surgery, not all warrant immediate removal as some may never become a problem. However, even small warts can become a problem if they bleed or become infected. Similarly what feels like a fatty lump can grow to such a size that it interferes with how the dog walks. Whenever a skin tumour is found it should be brought to the attention of your vet and monitored closely. The malignant skin tumours should be taken more seriously. Surgical removal at an early stage, when the tumour is still small, should be considered. If left, they will grow and will reach such a size that surgery cannot achieve a cure. In addition, malignant tumours can undergo secondary spread (metastasis) to local lymph nodes and more distant sites. The rate at which secondary spread occurs varies immensely between tumours. Certainly for some tumours, the larger they become the more likely they are to spread. Surgical removal of a tumour when it is small is most likely to be curative. Some malignant skin tumours may need other treatment such as radiotherapy or anti-cancer drugs to obtain better control or indeed cure. The common skin tumours in dogs include mast cell tumour, squamous cell carcinoma, sweat gland carcinoma, sebaceous tumours, lipoma, fibrosarcoma, haemangiopericytoma, melanoma and perianal adenoma. In the cat, the common skin tumours are squamous cell carcinoma, mast cell tumour, fibrosarcoma and ceruminous gland tumours within the ear canal. There is marked variation in behaviour of skin tumours. Laboratory assessment (histopathology) is required to identify the exact tumour type and thereby ascertain the prognosis. Surgery remains the most important treatment for most skin tumours but radiotherapy, and to lesser extent anticancer drugs, can also be used.

	MAMMARY TUMOURS IN CATS Mammary tumours are relatively common in middle aged and older unspeyed female cats. The majority of mammary tumours are malignant, grow quickly and frequently undergo secondary spread to other parts of the body with fatal consequences. What causes mammary tumours? Mammary tumours occur in mammary glands that have been exposed to female hormones. They are rare in cats spayed (ovario-hysterectomy) before their first season. As in dogs, mammary tumours of cats are preventable. In general, any cat that is not going to be used for breeding is best spayed before its first season to prevent mammary cancer and unwanted pregnancy. How could mammary tumours affect my cat? The majority of mammary tumours in cats are malignant. They tend to grow quickly over a matter of weeks to a few months and become inflamed, swollen and ulcerated. They can involve more than one gland and frequently spread to the adjacent lymph glands. Further secondary spread to the lungs, in particular, is also common and this is invariably fatal. Can mammary cancer of cats be treated? At an early stage when the tumours are small, wide surgical excision has the best chance of achieving a cure. This surgery may involve removal of all mammary tissue especially if there is more than one tumour. Anticancer drugs (chemotherapy) have been tried and can give some temporary relief when the tumour is ulcerated or too big to remove. Anticancer drugs have also been suggested to reducing the rate at which secondaries develop. To date the actual effectiveness of these drugs is not known. What is the prognosis? The majority of mammary cancers in cats are aggressive with a high secondary rate; therefore the prognosis has to be guarded. If lymph glands are involved at the time of surgery then the prognosis is very grave. Wide surgery when the tumours are small carries the best hope of a cure.

X-ray showing bone cancer in radius	BONE CANCER IN DOGS Bone tumours affect the larger breeds and are rare in small dogs. Irish Wolfhounds, Great Danes, Rottweilers and German Shepherd dogs seem to be at particular risk. To date, no genetic factors have been identified and it is thought that the growth characteristics of the at-risk breeds are important. Tumours tend to arise in the limb bones with the most active growth. The commonest sites are the distal radius (near the wrist), proximal humerus (near the shoulder), distal femur (above the knee in the back leg), proximal tibia (below the knee) and distal tibia (above the hock). Presentation Middle-aged dogs are more commonly affected. The first clinical sign that is noticed is either a sudden onset of lameness or a swelling at one of the characteristic sites. Not all sudden lameness and swellings are bone tumours - joint injuries such as sprains or ruptured ligaments can also cause these clinical signs. Veterinary attention should be sought at an early stage in all cases. With bone cancer, this lameness progresses and the dog may become 'grumpy' and off colour. Bone tumours become intensely painful, so much so that the dog can be severely affected by this. As the tumour grows, the swelling and lameness increase and routine painkillers give little or no relief. The commonest bone tumour is the type known as osteosarcoma - a malignant tumour arising from the bone cells. Less common tumours include fibrosarcoma (from fibrous tissue), chondrosarcoma (cartilage origin), and haemangiosarcoma (blood vessel origin). X-rays can be used to detect a bone tumour but laboratory examination of a biopsy is necessary to determine the exact nature of the tumour. Prognosis The prognosis for any bone tumour is grave. Without treatment, the primary tumour becomes so painful that euthanasia is the only humane option. Almost all bone tumours of the legs are malignant (cancerous) and therefore have the potential to spread. In the case of osteosarcoma, secondary spread to the lungs is an almost certainty but is rarely detected on x-rays at this stage. However, even when the primary tumour is removed, these secondary tumours continue to grow to such a size that severe breathlessness and a general malaise become over-whelming. Treatment options There is no simple treatment for bone tumours in dogs. Bone cancer is aggressive and therefore requires aggressive therapy to achieve any chance of success. However, in recent years, progress has been made. Pain relief is the first and foremost consideration. This can be achieved with analgesic drugs or by radiotherapy to the primary site. The pain relief achieved by radiotherapy tends to be better and of longer duration than by drugs but, even so, the pain is likely to start up again within the next 6 - 9 months. However, not all bone tumours are suitable for radiotherapy. Radiotherapy has no effect against the secondaries. Amputation is the only certain way of controlling the pain and the primary tumour itself. The pain associated with the tumour is often so severe that the dog is walking on three legs; if they can manage at this stage, they will be much happier and pain-free following amputation. Most dogs will cope very well with amputation; even Rottweilers and Great Danes will adjust to the loss of a forelimb. As an alternative to amputation, so-called limb-salvage operations have been tried where all of the affected bone is removed and replaced with a bone graft, a large metal plate and fusion of joint. This option is fraught with major complications and is rarely performed in Britain. Anti-cancer drugs following amputation are used to control the rate at which secondaries develop. With amputation alone, 60% of dogs will die from secondaries within six months; only 1 in 10 dogs will survive to one year. With the addition of anti-cancer drugs the six months’ survival is about 60%, with 4 in 10 alive at 12 months and about 15% alive at two years. Although generally well tolerated, the drug treatment can cause occasional side effects; some nausea and vomiting may occur after the treatment but this usually resolves within a couple of days. Currently the drug is administered once every 3 weeks for four doses You can contact us at Animal Cancer Trust 5 Flag Business Exchange, Vicarage Farm Road, Peterborough, Cambs PE1 5TX 08701 644225 www.animalcancertrust.org.uk info@animalcancertrust.org.uk Registered charity no. 1094779 Animal Cancer Trust is a Registered company limited by guarantee in England & Wales no. 04434009. The registered address of the company is Lacon House, 84 Theobald’s Road, London WC1X 9AA. Please use address above for correspondence.