Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Lung Cancer Happens in Pets, Too

Pet Column for the week of June 17, 2010

Related information:

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ashley Mitek
Information Specialist

Source - Alison P. Book, DVM
Everyone knows that smoking can cause lung cancer. Even second-hand smoke can cause the disease. But primary lung cancer, when the tumor originates from the lungs, in pets is relatively uncommon. On the other hand, metastatic tumors in the lungs (masses that have spread from a tumor elsewhere in the body) are a more common occurrence in veterinary medicine.

Dr. Alison Book is a veterinary oncology resident at the University of Illinois Veterinary Teaching Hospital in Urbana. She explains that, "primary lung cancer in dogs and cats is rare. As far as percentages go, it accounts for less than one percent of all the types of cancers that occur in pets." A certain type of tumor, a pulmonary adenocarcinoma, is the most common form that occurs in the lungs. Squamous cell carcinomas may also be diagnosed.

In recent years, research has shown that second-hand smoke in pets can contribute to lung disease in pets. However, in most cases of a primary lung tumor, the cause remains unknown. Owners may initially notice symptoms such as coughing, lethargy, decreased appetite, or exercise intolerance. Alternatively, these masses may be found incidentally on health screening.

If a veterinarian suspects lung cancer, radiographs (x-rays) are taken. If the tumor is large enough, a white circular mass will be seen on the image. It is very important that three images of the chest be taken when performing radiographs. Owners may wonder why just one image will not suffice for diagnostic purposes; without a right chest view, a left chest view, and a ventral-dorsal view (when the dog lies on its back), a radiologist could miss a tumor that is hidden behind a rib or other dense structure.

Dr. Book mentions that, "one small solitary tumor on radiographs, with no evidence of lymph node enlargement will do better than many larger tumors that have spread." In some cases of primary lung tumors, advanced imaging, such as a CT scan, can be performed to rule out masses elsewhere. If no other masses are found, surgery can be performed to remove the specific lung lobe that is affected. Even with advanced imaging and surgical treatment, the tumors may spread to other organs (sometimes smaller metastatic lesions are too small to be seen with diagnostic imaging).

Although primary lung cancer is uncommon, "there are many types of cancers that have a preferential site of spread to the lungs," mentions Dr. Book. Some of the classic cancers that frequently spread to the lungs are osteosarcomas and mammary tumors.

Experts are not exactly sure why so many cancers spread to the lungs, but there are a couple of theories. One hypothesis is that cells from the tumor that starts elsewhere in the body break off and then lodge in the small capillary bed in the lung vessels. Another theory is similar to a seed in soil--perhaps there is something in the lung tissue that particular tumor cells like, so they are able to grow in that particular environment.

For more information about cancer in pets, contact your local veterinarian.