Diagnosing Primary Lung
Tumors in Cats

Quick Facts at a Glance:

• Average age of onset is 10 years with a range of 6 to 18 years
• Poorly-defined interstitial and peri-bronchiolar lesion on radiographs
• Most commonly occurs in mid-caudal lung field
• Low grade cough is typically first symptom
• Often misdiagnosed as asthma in early stages
• Cytology from transthoracic aspirate often reveals numerous inflammatory cells
• Surgery in early stage of disease can result in long term survival
• Surgery in later stage of disease is associated with a >80% mortality rate

What are the clinical signs?

In the early stages of primary lung tumor, the feline patient may present to the family veterinarian with a history of an occasional cough and/or occasional wheezing. Weight loss typically has not yet occurred. The pet is still eating well, and often remains active. Radiographs are indicated at this stage and would raise the suspicion of a primary lung tumor. Unfortunately, because these symptoms are also consistent with asthma or other airway disease, radiographs are typically not performed until the later stages of disease. Treatment with prednisone with or without antibiotics is often initiated resulting in temporary alleviation of symptoms. Each course of treatment with prednisone and antibiotics is less effective at controlling symptoms than the cycle before. Ultimately the patient experiences significant weight loss, is persistently lethargic and tachypneic and has become anorexic. Surgical intervention (thoracotomy) in these advanced cases is associated with an extremely high post-operative morbidity resulting from a combination of emaciation, hypothermia, hypoventilation, hypotension, inadequate pain control, poor oxygenation, heinz body anemia, DIC and associated thromboembolic episodes and finally multi-organ failure. This disastrous combination of systemic events results invariably in death within days to weeks following surgery.

How does it appear on radiographs?

In the early stages of disease, radiographic changes most often consist of a moderate, ill-defined interstitial and peri-bronchiolar pattern generally confined to the mid caudal lung field. Inflammatory airway disease such as asthma generally affects the lungs more uniformly than what is found
with primary lung tumor. Less often, the tumor will be well delineated and therefore more readily diagnosed as a mass. In the later stages of disease, the interstial and peri-bronchiolar pattern in the mid-caudal lung field is more extensive and may involve more than one lung lobe. It typically remains ill-defined and therefore often misdiagnosed as an inflammatory or infectious condition.


Below: A solitary primary lung tumor in early stages. This tumor was completely removed with surgery.




Figure 2: Advanced, ill-defined primary lung carcinoma. The diagnosis was confirmed with a trans-thoracic aspirate.





How beneficial is a trans-thoracic aspirate and cytology?

The difficulty in achieving a diagnosis in these patients is further compounded by the marked inflammatory infiltrate associated with these tumors. Transthoracic aspirate for cytology allows confirmation of a diagnosis in less than 50% of patients because tumor cells are masked by a marked infiltrate of macrophages and neutrophils. This cytologic finding often further supports the clinicians erroneous diagnosis of inflammatory or infectious disease. When a cytologic diagnosis is possible, carcinoma (adenocarcinoma or squamous cell carcinoma) is confirmed.

Should surgery be performed?

Surgery remains the treatment of choice for primary lung tumor. However, stage of disease is important in predicting the surgical outcome. When the patient is in good general condition, has experienced minimal weight loss, is still active and eating well, surgical intervention is indicated and has an excellent chance of resulting in a successful surgical outcome. When the patient is emaciated, not eating, lethargic and markedly tachypneic, mortality rate post surgery is extremely high and therefore surgery is not advised.

What about chemotherapy?

Very little is known about the benefit of chemotherapy in patients with primary lung cancer. By the time a definitive diagnosis is made, it is often too late for surgery as the disease is very extensive, and the patient is already debilitated. Treatment with chemotherapy at this stage is very unrewarding. There is rationale for intervening with chemotherapy at a less advanced stage, if the patient is still eating but the disease is too diffuse for surgery. Chemotherapy drugs that hold promise in this situation include carboplatin, mitoxatrone and gemcitabine.

What are the histologic findings with this tumor?

Primary lung tumors in cats consist of carcinomas of bronchioalveolar origin, undifferentiated carcinoma and squamous cell carcinoma. Those tumors that are well defined when identifed and thus resectable tend to be well to moderately well differentiated bronchoalveolar carcinomas. Squamous cell carcinoma of the lung is invariably ill-defined and associated with a very poor prognosis.

This cancer can spread to the digits!

Primary subungual tumors and nail bed infections are extremely rare in cats. Painful swelling of the digits in cats is most often associated with an unusual phenomen of metastasis to this location. While the patient may present for lameness and swelling of the digit of one foot, careful physical examination invariably reveals swelling of other digits of the same or other feet. Carcinomas of a variety of histogenic origins have been associated with this phenomenon however primary lung tumors are among the most common to metastasis to the digits. When painful swelling of multiple digits is found, thoracic radiographs are indicated to rule out lung
neoplasia. _


Below: Metastasis from a primary lung tumor to multiple digits caused severe lameness in this patient.