Veterinary Medicine - March 2008 - (Page 155)

tion was 8.8%; the incidence reached as high as 25% in geriatric dogs at necropsy.15 The factors that may have contributed to the high incidence of primary lung tumors in this beagle colony were not identi ed but may have included genetic, dietary, and unique environmental factors speci c to the closed colony. Primary lung tumors occur most commonly in larger, older animals, with a mean age of 10 or 11 and 12 years in dogs and cats, respectively.2,4,5,8,12-14,16 Although no de nitive breed or sex predilection has been identi ed, boxers represented 37% of all lung tumor patients in one study,12 and in a feline investigation, older females were more often affected than males.10,14 Similar to people in which chemical carcinogenesis plays a prominent role in the genesis of primary lung tumors, a causal link is suspected to exist between smoking households and primary lung tumors in dogs, especially in mesocephalic and brachycephalic breeds.17 Moreover, dogs living in urban environments more commonly have lung tumors than do dogs in rural settings.4 This apparent environmental effect could re ect the greater pollutants within an urban environment or may simply be due to the greater population density of animals receiving routine veterinary care. In dogs, the right caudal lung lobe is the most common anatomical location of primary pulmonary neoplasia.5,6,8,10,13,16,18 This observed anatomical preference termining the exact topographical origin of lung tumors extremely dif cult.10,19 Instead, in veterinary studies, pulmonary carcinomas are generally divided into four subgroups—adenocarcinoma, squamous cell carcinoma, bronchial gland carcinoma, Dogs in urban environments more commonly have lung tumors than do dogs in rural settings. is thought to be a result of greater lung tissue mass, thereby increasing the likelihood for spontaneous mutations within the right caudal lung elds.12 In cats, the caudal lobes are also more commonly affected, but they tend to have an equal occurrence in the right and left lung elds.14 and alveolar cell carcinoma.4,10 Adenocarcinoma, regardless of tissue cell origin, is the most common histologic type in dogs and cats.2,4,10,12-14,16,19 In two studies, adenocarcinoma made up 74% to 77% of all primary lung tumors histologically examined.4,10 Other reports suggest adenocarcinoma is more common in people and cats and bronchoalveolar carcinoma is more common in dogs.5 Squamous cell carcinoma, which is the most common pulmonary neoplasm in people, is less common in companion animals, representing 6% and 4% of all of canine and feline lung tumors, respectively. Anaplastic carcinoma is the rarest morphologic subtype in dogs and cats,10 but it is still more common than primary mesenchymal lung tumors, which are extremely rare in dogs and cats.4,10,20 In a case report of four dogs with mesenchymal or mixed-cell-origin lung tumors, the age range was 4 to 15 years, with spayed females and castrated males in equal proportion.20 All tumors were in the right lung elds—two were hamartomas, one was a pulmonary chondroblastic osteosarcoma, and one was a biphasic pulmonary blastoma. Only the patient with the chondroblastic osteosarcoma had pulmonary metastasis visible on thoracic radiography. Both patients with hamartomas were alive at least one year post pneumonectomy.20 Other reports of canine sarcomas include an osteosarcoma, a chondrosarcoma, and a Spirocerca lupi-associated brosarcoma, HISTOLOGIC CLASSIFICATION Carcinomas are the most frequently diagnosed lung tumors, but consensus for the most common histologic subtype is lacking. This lack of agreement is partially attributed to researchers using differing classi cation schemes, precluding direct comparisons between historical and recent studies. In veterinary medicine, the simplest classi cation scheme is by general cellular morphology, which includes adenocarcinoma, squamous cell carcinoma, and anaplastic carcinoma.6,19 Primary lung carcinomas can also be organized by topographical location, inclusive of bronchial, bronchoalveolar, or alveolar carcinoma.6,10 Confusingly, some studies categorize bronchoalveolar carcinoma into a separate cellular morphologic subtype altogether.5,8,14 Although organizing primary lung tumors by topographical location is useful in people, veterinary pathologists do not recommend this classi cation scheme in companion animals because of the advanced stage of the disease at the time of diagnosis, which makes de- Kerry C. Rissetto, DVM* Pamela W. Lucas, DVM Timothy M. Fan, DVM, PhD, DACVIM (small animal internal medicine, oncology) Department of Veterinary Clinical Medicine College of Veterinary Medicine University of Illinois Urbana, IL 61802-4714 *Current address: Department of Veterinary Medicine and Surgery College of Veterinary Medicine University of Missouri-Columbia Columbia, MO 65211 VETERINARY MEDICINE March 2008 155

Table of Contents Feed for the Digital Edition of Veterinary Medicine - March 2008

Veterinary Medicine - March 2008 Contents Toxicology Brief Idea Exchange A Challenging Case An Update on Diagnosing and Treating Primary Lung Tumors CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - March 2008

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