Since 2010, cancer has officially become the leading cause of death in the world in humans (according to WHO), supplanting cardiovascular disease. A similar development is observed in dogs. A recent study showed that cancer was the leading cause of mortality in dogs in the United States (Fleming et al., J Vet Intern Med 2011). In some breeds (Bernese Mountain Dogs, golden retrievers, boxers), one dog in two will die from cancer. This increase in cancer diseases is linked to several factors:
- The strong inbreeding associated with the development of canine and feline breeds has favored the emergence of certain specific breed cancer diseases. The most striking example of this is the Bernese Mountain Dog: more than one in two Bernese Mountain Dogs will die as a result of cancer, and these will often be "the same diseases" (histiocytic sarcoma or lymphoma);
- In a paraoxal fashion, the efforts of veterinarians and owners (through improved diet, monitoring and vaccination) have contributed to the multiplication of cancer cases. By reducing mortality from infectious diseases, public road accidents, the incidence of cancer diseases has increased with the life expectancy of the animals;
- Finally, dogs and cats share our environment and our way of life. They are affected by environmental factors that favor the onset and development of certain cancers.
This change in the conditions afflicting pets is accompanied by a change in the perception of owners and veterinarians in relation to cancer. According to personal experience, some will consider cancer to be a life-threatening illness, for which any attempt at treatment is therapeutic. Conversely, an owner or veterinarian who has been confronted with a "cured" cancer disease will be more likely to accept a diagnostic and therapeutic approach for their animal. But these owners will often ask for a quality of care as close as possible to that proposed in humans. With the progress made in man in the treatment of many cancers, this demand is likely to increase in the years to come.
A change in the mentality of veterinarians must accompany this evolution of the canine population. Caring for an animal for a cancerous disease involves spending a lot of time with the owner, to explain:
1 - the nature of the disease, its possible progression over time;
2 - the nature of the proposed care, and their possible side effects;
3 - the notion of life expectancy and median survival associated with treatments. It is always difficult to predict the evolution of a cancer, and it is necessary to make it clear, if necessary by means of drawings, that if half of the animals live "longer" than the median, half will live unfortunately less Than this median. It is essential to explain that despite the best treatments and a "favorable" extension, some patients may not respond to treatment, have significant side effects (treatment or illness), or may have a second disease ( Tumor or not) that will aggravate a prognosis considered initially favorable.
4 - the type of treatment that can be proposed. The "curative" and "palliative" treatments are typically contrasted. This distinction is not based on life expectancy (a patient can live several years in very good conditions "despite a palliative treatment"), or on the cost, but more on the cumbersome nature of the care proposed to achieve a fixed objective in advance. A "curative" treatment is proposed for an isolated lesion with a low or controllable risk of metastasis in an animal with a satisfactory life expectancy (absence of significant intercurrent disease). Heavy treatment (major surgery, associated or not with a treatment of radiotherapy and / or chemotherapy) is then proposed, because the possible inconveniences related to this treatment (prolonged hospitalization, frequent return to the clinic ...) are "counterbalanced" by Life expectancy. It is acceptable to keep an animal hospitalized for two weeks or even a month if it is expected to be long (several years). We propose a "palliative" treatment, faced with an incurable lesion (because too extensive, metastasized or touching an animal that can not withstand a curative treatment). In this case, the main aim is to improve or maintain the quality of life of the animal. "Heavy" treatments are avoided, and one will then seek to have a treatment working quickly and without side effects. In this case, the lifetime is unknown, but this may be brief, but above all, it is important not to inflict treatment that can reduce the quality of life.
The decision to treat an animal for a cancerous disease depends on several factors, which must be taken into account:
1- what is the nature of the tumor and what is its extension. The prognosis depends not only on the name of the tumor but also on its local extension and the presence of any lesion at a distance. For example, prognosis for osteosarcoma is highly variable, depending on the species (osteosarcoma is less aggressive in cats than dogs), localization (lesions of the skull metastasize less often but are More often inoperable) and the presence of associated metastases. The prognosis will thus be very variable and the treatment will have to be adapted according to these results. Thus, in a dog with osteosarcoma of the limb, associated with the presence of pulmonary metastases, a "palliative" treatment will be proposed in order to maintain a satisfactory quality of life: this treatment involves carrying out an irradiation of the tumor lesion , In order to decrease the pain and associated lameness, and a chemotherapy treatment to slow the growth of tumor lesions. This treatment will effectively reduce pain in about 80% of cases and will be associated with median survival ranging from 6 months to almost one year. But no animal will be permanently cured by such treatment. Conversely, in a dog with osteosarcoma of the limb without pulmonary metastases, "curative" treatments can be proposed, with amputation or performing limb-retained surgery, always associated with a chemotherapy treatment. With this type of treatment, median survival ranges from 8 months to more than one year, with nearly 20% of the animals that will not have metastases within two years of diagnosis. In the same way, a dog with a jaw melanoma will not have the same prognosis according to whether or not it has pulmonary metastases. A dog with a non-metastasized rostral lesion without ganglionic or pulmonary metastases has a 50% chance of being alive at one year if surgery coupled with radiotherapy is performed. This probability falls to less than 10% if metastases are observed.
2- The animal presents intercurrent diseases that can affect its life expectancy or the treatments envisaged. An animal with heart disease will not be able to withstand certain treatments, including chemotherapy (particularly adriamycin in an animal with dilated heart disease), or heavy anesthesia associated with surgery. Brief, superficial and time-lapse anesthesia associated with a palliative radiotherapy protocol will, however, usually be well tolerated.
3- Does the owner agree to take on the treatment-related constraints? Treating an animal for cancer represents a test for the owner which includes:
- more or less frequent trips to the veterinarian, the treatment having to be carried out according to a schedule established in advance. Some care (radiotherapy in particular) can not be realized in the vicinity, these movements will sometimes be very important;
- more or less frequent hospitalizations and / or monitoring of excreta in order to avoid contaminating the environment with residues linked to chemotherapy treatments;
- an obvious emotional investment: the owner will be very hopeful about the success of the treatment, will present moments of doubt about the side effects of the treatment or the progression of the disease (loss of hair, loss of appetite, vomiting );
- a financial investment, which must be planned in advance: it is unnecessary to carry out a very accurate and informative extension report but costly if the owners can not subsequently pay the cost of the treatments;
4- Can the veterinarian and / or do they want to provide all or part of the treatment? A multidisciplinary team (including a veterinarian oncologist, internist, surgeon specializing in imaging etc.) is ideal for proposing an appropriate treatment plan, but the involvement of the treating veterinarian is essential. If he does not wish to carry out the treatment himself, he will direct the owner's decision to initiate or interrupt the treatment, as he often knows the animal and its owner better than the specialists.
If all the conditions are met, the management of a cancerous condition can be a source of satisfaction for all the participants. The best example is the treatment of multicentre lymphoma. This is a very serious disease, often affecting animals that are often young and in good shape. It is easy to "discourage" a generalized disease that progresses rapidly, does not respond to cortisone and is rapidly strengthened, and systematically leads to death in a few weeks without treatment. Many veterinarians might then be tempted not to treat these lymphomas, because the prognosis is not good. At the same time, very few veterinarians or owners are refusing to treat a dog with insufficient heart because the prognosis is not good. However, a dog with high-grade malignant lymphoma with no other pejorative prognostic criterion has more than a 80% chance of seeing this disease "disappear" if a chemotherapy treatment is initiated. Although this remission is mostly transient (only 10 to 20% of dogs will be "cured" by chemotherapy), the associated median survival ranges from 10 to 24 months and the disease remains invisible during the quasi- Throughout that period. According to the most recent study on the treatment of mitral valve disease (QUEST, J Vet Intern Med 2008), the most frequent cardiac disease in dogs, the median survival of the group receiving the best treatment does not reach nine Months, with a quality of life remaining mostly decreased despite treatment.
