Primary pulmonary neoplasia was diagnosed in 14 dogs presented to the California Animal Hospital for medical and surgical management of respiratory tract disease.
Locations of the primary tumor were the right caudal (six), left caudal (five), right accessory (two), and right middle (one) lung lobes. Complete lobectomy of the affected lung lobe using a mechanical stapling device was performed in all cases. The tumor types observed were adenocarcinoma (six), bronchoalveolar carcinoma (six), anaplastic carcinoma (one), and epidermoid carcinoma (one). Of the 14 dogs undergoing exploratory thoracotomy, two died within a 72 hour postoperative time period. The remaining 12 dogs were monitored from two to 24 months (mean= 10 months) postoperatively to determine surgical complication and recurrence rates. No evidence of recurrence of pulmonary neoplasia has been observed in these dogs through the follow-up period.
Pulmonary neoplasms may be primary or secondary. Metastatic neoplasms of the lung are seen more commonly than primary tumors. The incidence rate of primary lung tumors has been estimated at 5.6 per 100,000 dogs. Although primary pulmonary neoplasia is relatively rare, as dogs continue to receive better medical attention enabling them to live longer, an increased incidence of these tumors may be observed.
The average age at the time of diagnosis is 10.5 years with the condition predominantly occurring in dogs seven years of age and older. breed or sex predisposition to primary lung tumors has not been identified. A higher incidence of primary tumors has been observed in the right lung lobes, with the right caudal lobe most frequently affected.
Any component tissue of the lung may be the site of origin of a neoplasm. The most commonly occurring primary lung tumors in the dog originate from the epithelium of the terminal bronchioli.
The majority of primary lung tumors are carinomatous. Based on histologic structure, most pathologists subdivide primary lung tumors into adenocarcinoma, bronchoalveolar carcinoma, anaplastic carcinoma, and carcinoid tumors. Other rare primary lung tumors include neoplasms arising from connective or lympathic tissue, and mesenchymal tumors.
The clinical signs associated with primary pulmonary neoplasia are usually vague and nonspecific. Symptoms observed may include loss of stamina, fatigue, anorexia and weight loss. Other clinical signs may include dyspnea, non-productive cough, hemoptysis, and lameness as a result of hypertrophic pulmonary osteoarthropathy. Occasionally, thoracic radiography reveals pulmonary lesions suggestive of neoplasia as incidental findings.
The prognosis associated with primary pulmonary neoplasia in the dog is dependent upon several factors, including (one) the severity of clinical signs, (two) the presence or absence of hilar lymphadenopathy, (three) the presence or absence of distant metastasis and (four) the tumor type.
The purpose of this paper is to describe the pathogenesis and clinical course of 14 dogs with primary pulmonary neoplasia and their responses to compete lobectomy.
Materials and Methods:
Exploratory thoracotomy was performed on 14 dogs with primary pulmonary neoplasia between January 1994 and December 1985. The dogs were elected for surgery based on the presence of a solitary mass involving a single lung lobe, with no evidence of distant metastasis or extrapleural involvement. A complete physical examination, as well as hematologic and biochemical blood analysis and urinalysis were performed in each case. Thoracic and abdominal radiographs were performed to eliminate the possibility of a primary neoplasm with pulmonary metastasis.
Complete lobectomy of the affected lung lobe using the TA 30 or TA 55 mechanical stapling deviceA was performed in each case. Examination for air leaks was made by flooding the cut surface with warm lactated Ringer’s solution. Leaks were managed with simple interrupted sutures using #2-0 polypropylene.
Following complete lobectomy, the thorax was lavaged, the remaining lung lobes were expanded to eliminate atelectasis, a chest tube was placed, and the thorax was closed. The chest was evacuated of all air and if there was no accumulation of air or fluid in the thorax over the next 24 hours, the chest tube was removed.
Representative sections of neoplastic tissue from each dog were submitted for histologic examination and classification based on the World Health Organization’s classification of pulmonary neoplasms in man.
Follow-up physical examination and suture removal were performed two weeks following surgery in all dogs. Follow-up thoracic radiography was performed at intervals of four to six months. All patients were followed from a minimum of two months to a maximum of 24 months.
The results are given in Table 1. The average age of the dogs was 10.4 years (range = 3-14 years). There was no sex (seven male, seven female) or breed predilection. Clinical signs included coughing (five), dyspnea (three), and weight loss (two). There were no abnormal findings on physical examination in four dogs.
Of the 14 lung lobes removed, nine (64 percent) were on the right and five (36 percent) were on the left. Of those tumors affecting the right lung, six (67 percent) occurred in the caudal lobe, two (22 percent) occurred in the accessory lobe, and one (11 percent) occurred in the middle lobe. All five tumors affecting the left lung occurred in the caudal lobe.
Histologic examination revealed six adenocarcinomas (43 percent), six bronchoalveolar carcinomas (43 percent), and one epidermoid carcinoma (seven percent).
Two dogs died within a 72 hour postoperative time period because of cardiac arrhythmias non-responsive to anti-arrhythmic cardiac therapy.
Three dogs were euthanized because of unrelated causes (degenerative myelopthy – two, caudal cervical vertebral instability – one) and one dog died because of unrelated causes (renal failure). Survival time of these dogs ranged from four to 24 months (mean = 11.5 months). At the time of euthanasia or death, these dogs were asymptomatic from signs of recurrent respiratory tract disease.
Eight dogs are currently alive and free from signs of recurrent or progressive respiratory tract disease at two to 24 months (mean = 9.3 months) following surgery. Thoracic radiography performed every four to six months has revealed no evidence of recurrence.
Primary pulmonary neoplasms have been reported to occur predominantly in dogs over seven to eight years of age. The results of this study support this finding. No sex or breed predisposition to primary lung tumors have been identified. In this study, males and females were represented equally. Although no one breed was affected more frequently than others in this study, all of the dogs were medium to large size breeds with the exception of case #3. Further case studies were necessary to determine if this is either a significant trend or because of the predominance of medium to large breed dogs within our referral population.
Clinical signs associated with primary pulmonary neoplasia are often vague and nonspecific. It has been reported that as many as 33 percent of primary lung tumors are discovered during a physical or radiographic evaluation for another problem. There were no abnormal findings on physical examination in four of the 14 dogs (29 percent) in this study.
The most common clinical sign (five cases, 36 percent) was a non-productive cough. This is in agreement with the findings of previous investigators. Dyspnea (three cases, 21 percent) or weight loss (two cases, 14 percent) was the primary owner complaint in the remaining five cases.
It has been reported that the absence of clinical signs in man and dogs with primary pulmonary neoplasia is a favorable prognostic indicator. Because of the small sample size and length of the follow-up period a similar conclusion could not be drawn from the results of this study.
A number of investigators have reported a majority of primary pulmonary neoplasm affecting the right lung, with the right caudal lung lobe having the highest incidence of primary tumors. The results of this study are in agreement: 64 percent of the tumors were on the right side, with the right caudal lobe affected in 43 percent of the cases.
Histologic examination of primary lung tumors in dogs has indicated that nearly all lung tumors are malignant. Adenocarcinomas have been reported to be the most commonly occurring lung malignancy (75 to 83 percent). Epidermoid (squamous cell) carcinomas (six to 12 percent) are less common, as are anaplastic carcinomas (four to nine percent). This is in contrast to man, where squamous cell carcinoma (30 to 35 percent) is more common than adenocarcinoma (25 to 29 percent).
In this study, bronchoalveolar cell carcinomas (43 percent) occurred as frequently as adenocarcinomas (43 percent). Because of the small sample size, these results must be interpreted with caution. Anaplastic carcinoma (seven percent) and epidermoid carcinoma (seven percent) occurred less frequently.
In many dogs, the confirmation of primary lung tumor may be shortly followed by premature euthanasia. It is the authors’ opinion that surgery is often indicated in the treatment of primary pulmonary neoplasia. The results of this study demonstrate that surgical excision of the affected lung lobe can lead to prolongation of good quality life.