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.


2. A lateral thoracic radiograph of an 8-year-old spayed female Labrador retriever presented for evaluation of a decreased appetite and lethargy of four weeks' duration. Multiple soft tissue opacities affecting the pulmonary parenchyma are identified, which were cytologically consistent with bronchoalveolar carcinoma. (Photograph courtesy of Dr. Laura Garrett.)
In cats, adenocarcinomas tend to manifest either as a well-circumscribed, cavitated mass in the center or periphery of the lobe or as a localized (lobar) alveolar pulmonary infiltrate that is often calcified (25% of cases). Bronchoalveolar carcinomas occur as pleomorphic, multifocal, or diffuse opacities located in the middle to peripheral portions of the affected lobes, with two-thirds of cases having pleural involvement on radiographs. Unlike in dogs or people, squamous cell carcinomas in cats show extreme variability in radiographic pattern but tend not to be hilar in origin.14

Despite certain growth and distribution patterns associated with primary lung tumors in companion animals, it remains impossible to definitively classify such tumors based purely on topographic anatomy, mostly because, as mentioned earlier, canine and feline neoplasms are often too advanced at diagnosis to identify their anatomical site of origin.5,12 This limitation has been underscored in several veterinary studies in which no correlation was found between a tumor's location and its histologic subtype. Thus, once a pulmonary mass has been identified on initial thoracic imaging, histologic or cytologic evaluation of the suspect lesion is absolutely necessary for definitive diagnosis.8,16,19


The clinical signs of primary lung tumors depend on many factors such as tumor invasiveness, the extent of lung tissue involvement, the presence of metastatic disease, and the occurrence of paraneoplastic syndromes.


The most common sign in dogs is a nonproductive cough, occurring in 52% to 58% of dogs with a primary lung tumor.2,4,8,12 Other respiratory signs may include tachypnea, wheezing, exercise intolerance, and hemoptysis. Nonspecific signs in dogs are common and include lethargy, weight loss, and anorexia.2,4 Dyspnea may occur if a large portion of the lung is involved or if pneumothorax, pleural effusion, or concurrent disease (congestive heart failure or tracheal collapse) is present.1,8 Severe lameness and pain may also be a presenting complaint if hypertrophic osteopathy or bone metastasis has occurred.1,2,4,12 Despite many patients presenting with overt clinical signs associated with primary lung tumors, up to 30% of all dogs will have no signs of disease at the time of diagnosis.2,4,12


Clinical signs seen in cats with primary pulmonary neoplasia are extremely variable, but dyspnea, weight loss, lethargy, anorexia, weakness, and vomiting are frequently reported.16,27 In one study of 35 cats with primary lung tumors, about 25% of cats presented with lameness, likely resulting from digital skeletal metastasis associated with primary pulmonary carcinoma. Respiratory signs were noted in only one-third of the cats, and coughing was rarely reported.1 In contrast, another feline study found that all 86 cats had at least one clinical sign directly or indirectly related to their primary lung tumor, and 53 of the cats (61.6%) had signs of respiratory difficulty.16 In general, cats with primary lung tumors present with a wide range of clinical findings, and the absence of overt pulmonary signs should not preclude a primary lung tumor as a differential diagnosis.


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