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veterinary medicine

Victims of time

Researchers perfect treatments for cancer in dogs, and they are living longer and longer

EDUARDO CESARGerman shepherd dog: one of the races most susceptible to cancer EDUARDO CESAR

Better treated then ever, with special feeds, vaccines, physiotherapy and even psychological accompaniment, dogs are living longer. It may be good for their owners, but living longer brings a problem: it increases the risk of cancer, seen today as one of the main causes of death amongst domestic animals, which kills over half of the dogs and a third of the cats brought up in American homes. It is a problem in Brazil as well, where some 28 million dogs live (almost half the canine population of the United States) and 12 million cats, regarded as elderly and more subject to cancer after they are 7 or 8 years old.

Alert to this situation, researchers from the College of Agrarian and Veterinary Sciences (FCAV) of the São Paulo State University (Unesp), in Jaboticabal, are creating alternatives, in accordance with the world-wide trend, for treating and if possible curing domestic animals attacked by the disease, for whom a few years ago there would be only one way out: they would be put to sleep.

Instead of amputation, the standard treatment in cases of osteosarcoma, a tumor responsible for 85% of the occurrences of bone cancer, the team from Unesp is showing the feasibility, in many cases, of bone implants, which tends to become more efficient with the use of new materials. In a study published in March in Acta Cirúrgica Brasileira, a group of six veterinarians from Unesp attests to the possibility of using, in Brazil, a polyurethane resin from castor beans, as a cement for the implant of bone fragments taken from healthy donors and preserved in glycerin at room temperature. This material replaces another resin, polymethylmethacrylate, which releases toxic gases, throws off heat (as high as 70° Celsius) and may set off cardiac arrhythmias.

Cement for bones
The results are supported by an experiment with six dogs (four males and two females) of no particular race, in whose tibias (the bone equivalent to the shinbone in a human leg) the implant was made. Five of the six animals treated put their weight on the operated leg on the first day after the implant, and were running normally after a month and a half, on average. In this study, the resin from castor beans a whitish paste used to fill the graft, where the bone marrow had been removed provided greater resistance in fixing the metal plate that makes the implant adhere to the original bone. And it did not unleash any infectious processes, a result attributed to the animals good state of health.

In other studies in which the same surgical procedures were followed, with the exception of the bone cement, adopted experimentally about six years ago in the United States, one third of the animals treated, on average, showed infections. In the experiment carried out at Unesp, it was also seen that the resin was not absorbed, nor was it replaced by new bone tissue. By acting as a bactericide, it did away with the use of antibiotics, which are indispensable with the previous resin, polymethylmethacrylate.

All this evidence means positive indicators for the resin from castor beans to be used as a bone cement on a larger scale, in future, by veterinary clinics. But, warns Carlos Roberto Daleck, from Unesp’s team, implants are an alternative to amputation only if at least half the bone is left over – the osteosarcoma, more common in the larger sized races, like St. Bernards or Dobermans, is a very aggressive tumor, which often leads to the disintegration of the bones. The preservation of the affected bones also takes into account the well being of the animals’s owners. “There are cases where it would be simpler to amputate the affected member and the animal would leaving the clinic walking happily on three legs”, says Daleck, “but the idea of mutilation usually gives the dog’s owner nightmares”.

In another recent study, to be published in Acta Cirúrgica, carried out with two groups of six dogs, the team from Unesp in Jaboticabal showed that a medicine called furosemide can attenuate the unwanted effects, above all the alteration in the workings of the kidneys, caused by cisplatin, a chemotherapeutic agent adopted for treating cancer of the bones, bladder and testicles in dogs, for example.

Another work, published last year in Arquivo Brasileiro de Medicina Veterinária e Zootecnia [Brazilian Archives of Veterinary Medicine and Zootechny], reiterates the importance of early treatment, by detailing the possibilities of differentiating, by means of an examination using a transmission electron microscope, the alterations that occur in a kind of cell in the skin called mastocytes: as the tumor evolves, the nucleus of these cells increases in volume, granules arise in the cytoplasm, and the rugosity of the membrane becomes more evident. On the basis of these parameters, the team from Unesp cured 60% of the 108 dogs with mastocytoma attended to in the last four years; this is the most common kind of skin cancer, which particularly affects bulldogs and boxers after the age of 8.5 years.

It is very difficult to find out precisely which races are most affected and the most common kinds of cancer amongst dogs in Brazil. A survey published in Archives of Veterinary Science, based on 333 dogs attended to in the veterinary hospital of the Federal University of Paraná (UFPR) between 1998 and 2002, indicated that females are more susceptible than males, in a ratio of two to one. Breast tumors predominate, found in almost half the females (45.6%), and what is worse, in the majority of cases (68%), the tumors are malignant. According to this study, coordinated by Suely Rodaski, this predominance may be associated with the use of hormones as a contraceptive method, and the little attention given to early neutering the removal of the ovaries and uterus before the coming on heat for the first time reduces the risk of the appearance of breast cancer to almost zero.

The team from Paraná also found that, amongst dogs of a certain race, cancer is most frequent in German shepherd dogs (12.61% of the cases attended to), poodles (11.41%) and boxers (10.81%), with the greatest incidence amongst animals between 6 and 12 years old. When submitted to surgery and chemotherapy, they get an average extra lease of life of 19 months.

The Project
Chemotherapy with Cisplatin on Dogs (nº 00/03015-9); Modality Regular Line of Grants for Research; Coordinator Carlos Roberto Daleck – FCAV/Unesp; Investment R$ 42,103.55