Tuesday, May 13, 2008

Lung Cancer in Cats

Quick Facts at a Glance:

Average age of onset is 10 years with a range of 6-18 years Poorly-defined lesion on chest radiographs Most commonly occurs in mid-caudal lung field Low grade cough is typically first symptom Often misdiagnosed as asthma in early stages Cytology (needle sample) from trans-thoracic 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 greater than 80% mortality rate.

What are the clinical signs?

In the early stages of primary lung tumor, the feline patient may be 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. X-rays 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, x-rays 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, becomes persistently lethargic, has increased respiratory rate and stops eating. Surgical intervention (thoracotomy) is these advanced cases is associated with an extremely high post-operative decline and death resulting from a combination of emaciation (wasting away from lack of nourishment), hypothermia, hypoventilation, hypotension (low blood pressure), inadequate pain control, poor oxygenation, heinz body anemia (disorder of the red blood cells), DIC (disseminated intravascular coagulation or inability to clot blood) and associated thromboembolic (blood clots that break loose in the bloodstream, causing blockage) episodes and finally multi-organ failure. This disastrous combination of systemic events results invariably in death within days to weeks following surgery.

How does is appear on x-rays?

In the early stages of disease, radiographic changes most often consist of a moderate, ill-defined interstitial and peribronchiolar 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 interstitial and peribronchiolar 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 is misdiagnosed as an inflammatory or infectious condition.

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 (large areas with abundant inflammatory cells) associated with these tumors. Trans-thoracic aspirate for cytology allows confirmation of a diagnosis in less than 50% of patients because tumor cells are masked by a marked infiltrate of these inflammatory cells. This cytologic finding often further supports the clinician's 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 (very thin), not eating, lethargic and very obviously breathing harder, death 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, mitoxantrone and gemcitabine.

This cancer can spread to the digits!

Primary subungual (under the toenail) tumors and nail bed infections are extremely rare in cats. Painful swelling of the digits (toes) in cats is most often associated with an unusual phenomenon of metastasis (spread) to this location. While the patient may present for lameness and swelling of the digit of one foot, careful physical examination invariable reveals swelling of other digits of the same of other feet. Carcionomas of a variety of histogenic origins have been associated with this phenomenon; however, primary lung tumors are among the most common to metastasize to the digits. When painful swelling of multiple digits is found, chest x-rays are indicated to rule out lung neoplasia (cancer).

©This information sheet was donated by Dr. Robyn Elmslie of the Veterinary Referral Center of Colorado. To find out more about this hospital go to www.vrcc.com.

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