Veterinary Oncology

Small Animal/Exotics

20TH ANNIVERSARY

Compendium October 1999

Highlights and Horizons in

Veterinary Oncology E. Gregory MacEwen, VMD, Diplomate ACVIM (Internal Medicine, Oncology) Professor, Department of Medical Sciences School of Veterinary Medicine University of Wisconsin Madison, Wisconsin he field of veterinary oncology has grown considerably over the past 20 to 30 years. Today, cancer treatment in companion animals continues to undergo a substantial evolution within clinical veterinary practice. It is estimated that 15% to 20% of mature animals presented to a veterinary practice will have a neoplastic process. Following diagnostic workup, 20% to 25% of those patients will receive cancer treatment.

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History In the late 1960s and early 1970s, veterinary oncology was dominated by pathologists and, to a limited degree, academic veterinary surgeons. The advances made during this time were predominantly pathologic classification schemes and tumor grading systems. The development of traditional surgical management of solid tumors served as the basis for gaining information on the biologic behavior and sites of metastasis for many common cancers. When I entered the field of veterinary oncology in the early 1970s, the primary objective for most aggressive cancers was to establish a diagnosis and obtain a complete necropsy. In the late 1970s, clinical staging systems were established under the leadership of the World Health Organization. These staging systems were essential for the development of prospective clinical trials, for valid comparisons among treatment modalities and studies performed by various investigators, and for maintaining consistency in the presentation of data in the literature. Surgical oncology advanced significantly in the 1980s; the most notable contributions included advances in the aggressive treatment of oral tumors (e.g., mandibulectomy, partial maxillectomy) and limb-salvage procedures. Slowly, the field of nonsurgical cancer therapy began to develop. Particularly at a few schools of veterinary medicine (e.g., Colorado State University, North Car-

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ANNIVERSARY

1968 The seminal paper on cancer incidence data for dogs and cats is published in the Journal of the National Cancer Institute

1974 The Veterinary Cancer Society (VCS) is established

E. Gregory MacEwen, VMD

olina State University), radiation therapy advanced because of the potential for using companion animals as models for human cancer. Over the past 20 years, there have been significant technical refinements in radiation therapy in humans as the result of experience gained in veterinary practice. For example, investigators at Colorado State University obtained substantial grant support from the National Cancer Institute in the mid-1970s

1978 The World Health Organization publishes the TNM (tumor, node, metastasis) classification of tumors in domestic animals

1980 Purdue University hosts the first VCS Clinical Veterinary Oncology Workshop

19 1985

1980 1983

1979

1981

1982

The National Institutes of Health publishes the first and only monograph on the occurrence of tumors in domestic animals

1984

19

Compendium October 1999

20TH ANNIVERSARY

and early 1980s for the study of animal models and obtained new data on tumor response, tumor hypoxia, fractionation techniques, and normal tissue toxicity in companion animals. The field of veterinary medical oncology struggled in the 1970s because of the lack of veterinary centers focusing on medical oncology. Initially, the major challenges were to identify available chemotherapeutic agents, determine dose levels that were well tolerated, establish frequencies of administration, determine appropriate monitoring for drug toxicity, and conduct clinical trials to determine efficacy. In the late 1970s and early 1980s, a number of available chemotherapeutic agents (e.g., L-asparaginase, doxorubicin, vincristine, cyclophosphamide, melphalan) tested in prospective clinical trials were shown to have antitumor activity in animals for lymphoma, chronic leukemias, myeloma, and a few solid tumor types. Following the identification of the best agents, such as those listed above, the next challenge was to combine these drugs into combination chemotherapy protocols. In the mid-1980s, combination chemotherapy protocols had become the standard of care for medical oncology in human and veterinary medicine. Since the late 1980s and early 1990s, combined-modality therapy, which includes surgery, radiation, and chemotherapy, has become more common in the general practice of veterinary oncology. The use of immunotherapy and biologic therapy has its roots in the mid-1970s; however, the results of a number of clinical trials yielded only minimal benefit in treating a few selected solid tumors, such as osteosarcoma, melanoma, and lymphoma. None

Small Animal/Exotics

of the targets of current anticancer drugs are cancer-specific; DNA and RNA synthesis, microtubule assembly and function, and topoisomerases are common targets for anticancer drugs but are also required by normal cells, especially those that grow rapidly (e.g., in bone marrow and the gastrointestinal tract). However, as our understanding of the molecular biology of cancer and the role of the tumor microenvironment or tumor–host interaction increases, enthusiasm for biologic therapy, gene therapy, organ-specific targeting, and immunotherapy will intensify. Some of the most exciting advances in cancer therapy, such as antiangiogenic agents, tumor vaccines, growth factor receptor inhibitors, and liposome-encapsulated chemotherapy, are based on a better understanding of the biology of cancer and the selection of agents with defined mechanisms of action.

Organizations The advancement of veterinary oncology is also based on organized veterinary medicine. The most notable impact on clinical veterinary oncology was the establishment of the Veterinary Cancer Society (VCS) in 1974. The VCS grew from a small group of approximately 20 to more than 600 members today. This organization has played a major role in the dissemination of new knowledge through its annual scientific meetings and the publication of the Veterinary Cancer Society Newsletter. The VCS has also helped to develop veterinary oncology into a recognized specialty within the American College of Veterinary Internal Medicine (ACVIM). In 1987, the ACVIM

OWNERS’ OUTLOOK ■ Family Ties. Studies conducted by Barker and Barker showed that some dog owners are as emotionally close to their dogs as to their closest family member. More than one third of owners in the study felt closer to their dogs than to any human family member.1,2

References 1. Barker SB, Barker RT: Investigation of the construct validity of the Family Life Space Diagram. J Ment Health Couns 12:506–514, 1990. 2. Barker SB, Barker RT: The humancanine bond: Closer than family ties? J Ment Health Couns 10:46–56, 1988.

established oncology as a subspecialty within its organization. Today, there are more than 90 board-certified ACVIM diplomates in oncology. In 1994, the American College of Veterinary Radiology established radiation oncology as a separate board, and there are currently 30 board-certified veterinary radiation oncologists. An additional significant contribution to veterinary oncology was the establishment of the Veterinary Cooperative Oncology Group (VCOG) in 1985. This group was established to enhance interactive collaboration and multicenter trials to broaden the generation of clinical data and therapeutic studies. The VCOG has conducted a large number of retrospective and prospective clinical studies, most of which have been published in the veterinary literature.

1992 1995 987 1998 1994 1991 986 19891993 1997 1985 The American Veterinary Medical Association publishes a brochure entitled Warning Signs for Cancer in Pets

1990

The Veterinary Cooperative Oncology Group is founded

1987 The American College of Veterinary Internal Medicine recognizes oncology as a specialty, and the certification process is established

1990 The European Society of Veterinary Oncology (ESVO) holds its first annual congress

1994 The American College of Radiology establishes the subspecialty of radiation oncology

1999 The VCS and the ESVO hold their first combined international meeting

1999

Small Animal/Exotics

20TH ANNIVERSARY

Private Practice Although the majority of contributions made to veterinary oncology have originated from oncology programs at academic veterinary institutions, the field has extended greatly into the private sector. The rapid development of specialty practices in almost all major metropolitan areas has moved cancer management from academic centers to private practice. Not only has medical oncology expanded to private practice, but radiation therapy is now becoming readily available in private specialty practices. Based on the economics and demographics of veterinary practice, the greatest expansion of the delivery of veterinary cancer care in the future will most likely take place in private referral practice. The academic centers will still play a major leadership role in resident training, research, and conducting prospective clinical trials. For academic programs to remain viable and competitive, however, close collaboration will be needed with the private sector. Client Attitudes Concurrent with the rapid expansion of clinical veterinary oncology, clients’ attitudes toward cancer and cancer therapy for their companion animals have changed at a similarly rapid pace. Much of this is a direct result of the awareness and appreciation by veterinarians of the strong bond that develops between owners and their pets. In ad-

Compendium October 1999

dition, veterinarians now have a more positive attitude and philosophy regarding cancer therapy. Finally, veterinary care has shifted toward life extension and the improvement in quality of life. General veterinary practice has eliminated many juvenile diseases, and pets are living to a ripe old age. Pet owners are generally knowledgeable, and many have a strong appreciation for the various modes of cancer therapy, related toxicities, and potential benefits.

The Future The next 20 years will bring a phenomenal number of exciting changes to veterinary oncology. There will be a greater shift toward cancer-specific therapies and less reliance on traditional chemotherapy and radiation. These therapies will include gene therapy, targeted chemotherapy, antiangiogenic therapy, focused radiation, and cancer-specific drugs. Furthermore, the availability of reliable and factual information via the Internet will allow pet owners to have immediate and up-to-date information, which may give them as much knowledge as practitioners have about a particular cancer or treatment modality. This will create a major challenge for practicing veterinarians. The availability of current information and access to veterinary specialists via the Internet and telemedicine will play an even greater role in expanding oncology into the private sector.