An update on diagnosing and treating primary lung tumors - Veterinary Medicine
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An update on diagnosing and treating primary lung tumors
The incidence of this rare cancer in dogs and cats may be on the rise. Find out how to spot a primary lung tumor and what new forms of therapy may soon be at your disposal.


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.)
Primary pulmonary adenocarcinomas in cats appear to have a higher rate of metastasis than those in their canine counterparts and may be partially explained by a higher incidence of poorly differentiated adenocarcinomas in cats.5,10,16 In a study of 86 cats, 75.6% had evidence of metastatic disease at the time of diagnosis. Twenty-five 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

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.)
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, specifically 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


8. A lateral thoracic radiograph of the cat in Figure 6 identifies a soft tissue opacity (arrows) involving the left caudal lung lobe. (Photograph courtesy of Dr. Laura Garrett.)
The World Health Organization's tumor, node, metastases (TNM) classification scheme for staging tumors has great value when predicting survival time.


9. A fine-needle aspirate of a pulmonary mass identifies a cohesive population of basophilic, epithelial cells with squamous differentiation in a background of suppurative inflammatory cells. Multiple criteria of malignancy are evident, including anisocytosis and an increased nuclear to cytoplasmic ratio, consistent with primary pulmonary squamous cell carcinoma. Pulmonary squamous cell carcinoma is often associated with metastasis to the digits in cats. (Wright's stain, 500X). (Photograph courtesy of Dr. Laura Garrett.)
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

Table 2: Comparison of Canine Survival Times in Three Prognostic Studies
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 (5 cm diameter) had the greatest mean survival time of 20 months (median 17.5 months) compared with 7.8 months (median 8.5 months) for patients with tumors > 100 cm3.8


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