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.)
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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
CLINICAL SIGNS
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.
Dogs
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
Cats
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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