Veterinary Medicine - March 2008 - (Page 163)

Primary lung tumors PEER-REVIEWED 5. A thoracic computed tomographic image from a 12-year-old castrated male domestic shorthaired cat presented for evaluation of inappetence and weight loss. A cavitated mass (arrows) is identiﬁed in the periphery of the right caudal lung lobe. The mass was removed with thoracoscopic lung lobectomy, and the histologic examination results revealed a well-differentiated adenocarcinoma. (Photograph courtesy of Dr. Kristen O’Dell-Anderson.) 86 cats, 75.6% had evidence of metastatic disease at the time of diagnosis. Twentyve cats (29%) had bronchial lymph node metastasis, while 40 cats (46.5%) had distant metastasis involving the pleural cavity or extrathoracic sites including the skeletal muscle, skin, liver, spleen, brain, kidneys, intestines, and bone.16 The mode of metastasis in feline primary lung tumors is poorly understood, but clinical evidence supports lymphatic and hematogenous routes of metastasis.41,42 Although not a common site of metastasis for primary lung tumors in dogs, the digit is a frequent metastatic site in cats with primary lung tumors, speci cally squamous cell carcinoma, and is referred to as lung-digit syndrome (Figures 6-9). In a study of 64 cats examined for lytic digital lesions, only eight had primary digital carcinoma, while the remaining 56 cats (87.5%) had digital metastases of a primary pulmonary carcinoma. The preponderance of digital cancers being metastatic foci greatly emphasizes the need for thorough staging, especially thoracic imaging, before amputating suspected digital tumors in cats.42 6. An 11-year-old castrated male domestic longhaired cat presented for evaluation of recurrent nail bed infection and pain involving the third digit. Removal of the diseased toenail revealed a small, nonhealing wound. (Photograph courtesy of Dr. Laura Garrett.) 7. A radiograph of the right front foot of the cat in Figure 6 reveals bony destruction involving the third digit (long arrow) and soft tissue swelling (short arrows). (Photograph courtesy of Dr. Laura Garrett.) PROGNOSTIC FACTORS The World Health Organization’s tumor, node, metastases (TNM) classi cation scheme for staging tumors has great value when predicting survival time. Dogs Metastasis to the tracheobronchial lymph nodes is the single best predictor of remission and survival time for dogs with primary lung tumors treated with surgery.2,3 Median survival times in dogs with positive tracheobronchial lymph nodes based on histology range from 26 to 255 days, while patients with no lymph node involvement achieve median survival times ranging from 120 to 452 days.2,3,8 When lymph nodes were assessed before or during surgery, dogs with enlarged nodes survived a median of 60 days, while patients with normal size nodes had median survival times ranging from 285 to 345 days.3 Several additional variables were found to affect prognosis when evaluated simultaneously, including histologic score, regional lymph node involvement, and detection of clinical signs (Table 2). For histologic score, patients with differentiated adenocarcinomas had median survival times ranging from 251 to 495 days, while patients with other tumor types survived between 44 and 240 days.2,3,8 In patients in which clinical signs were detected at presentation, median survival times ranged from 240 to 300 days, while asymptomatic dogs achieved much longer survival times ranging from 545 to 900 days.2,8 In one study, tumor size also showed some correlation to prognosis. Patients with a primary tumor size 100 cm3.8 Cats Because cats tend to have a higher incidence of poorly differentiated adenocarcinomas,10,16 it is not surprising that cats with primary lung tumors usually do not survive as long as dogs do. In a study of 21 cats treated with surgical resection, only histologic differentiation of the primary lung tumor had a signi cant correlation with survival time.27 Twelve cats with moderately differentiated tumors (57.1%) had a median survival time of 698 days, while nine cats with poorly differentiated tumors (42.9%) had a median survival time of 75 days. Although the study had inadequate power for statistical analysis of lymph VETERINARY MEDICINE March 2008 163

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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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