The Enemy Within. A Dog’s Battle with Cancer Revealed in X-rays


Cancer is unfortunately very common in dogs, with approximately 1 in 3 dogs developing cancer during their lifetime. While cancer was previously considered a death sentence for dogs, advancements in veterinary medicine have led to more treatment options and improved prognosis for many canine cancers.

One of the most useful diagnostic tools for detecting cancer in dogs is x-ray imaging. X-rays create images of structures inside the body using radiation, and allow veterinarians to identify tumors or abnormalities that may indicate cancer. X-rays are minimally invasive, relatively affordable, and provide immediate images that give vets an initial glimpse into what may be going on inside the dog’s body.

While x-rays do not definitively diagnose cancer, they are often the first test ordered when a veterinarian suspects cancer as a possibility. X-rays can help locate tumors in areas like the chest, abdomen, and bones, alerting vets to the presence and spread of cancer. They also assist in determining the stage of cancer and serve as a baseline for comparison when monitoring treatment. This article will provide an in-depth overview of using x-rays to detect and evaluate canine cancer.

What is Cancer in Dogs?

Cancer is characterized by abnormal and uncontrolled cell growth that spreads to surrounding tissues. There are many types of canine cancers, but some more common ones include:

Lymphoma – This cancer affects the lymph nodes and lymphatic system. It is one of the most frequently diagnosed cancers in dogs (

Mast Cell Tumors – These abnormal growths develop from mast cells in the skin, gastrointestinal tract, and other areas. Mast cell tumors are the most common skin tumor in dogs (

Hemangiosarcoma – This cancer arises from blood vessel cells and often affects the spleen, heart, or skin. It can spread rapidly (

Osteosarcoma – The most common bone cancer in dogs, osteosarcoma typically develops in the limbs. It is an aggressive cancer that can spread to the lungs and other areas (

Risk factors for canine cancers include age, breed, genetics, and environmental exposures. Senior dogs are more prone to developing cancer than younger dogs.

Using X-Rays to Diagnose Cancer

X-rays are a valuable tool for veterinarians to diagnose cancer and other diseases in dogs. Here’s how they work and what vets look for:

X-rays use electromagnetic radiation to create images of the inside of the body. The x-ray machine sends a narrow beam of x-rays through the dog’s body. The rays pass through soft tissues but are absorbed by dense structures like bone. The differing levels of absorption are what create the image.

dog getting an x-ray

On an x-ray, tumors and cancerous masses often appear as abnormal masses or swellings. Lung tumors may look like round opaque spots. Bone cancer can cause areas of bone destruction or abnormal bone growth. Lymphoma often presents with enlarged lymph nodes.

One of the main benefits of x-rays for cancer diagnosis is that they allow vets to see tumors in the chest and abdomen that may not be palpable from the outside. X-rays provide important information about the location, size and shape of tumors that can’t be physically felt during an exam.

X-rays are relatively quick, painless and inexpensive compared to other imaging techniques. They are readily available at most vet clinics and animal hospitals, making them one of the first diagnostic tests vets utilize when cancer is suspected.

Interpreting X-Ray Results

Interpreting x-rays requires training and an understanding of what normal structures look like. Veterinary radiologists look for abnormalities that could indicate cancer, such as:

– Masses or tumors – These appear as areas of increased opacity or densities on the x-ray. Malignant tumors often have irregular or poorly defined borders. Benign masses tend to have smooth, well-defined borders.

– Evidence of metastasis – Metastatic cancer will cause changes like increased density in the lungs from tumor nodules. Lymph nodes may appear enlarged on x-rays when cancer spreads.

– Bone changes – Primary bone tumors or cancer that has metastasized to bone can cause abnormal bone density or the appearance of bone destruction on x-ray.

– Evidence of compression or obstruction – Tumors that are pressing on organs, airways, or vessels may be visible on x-rays.

In a normal chest x-ray, the lungs should appear light and clear, the heart and major blood vessels are visible, and the bronchial tree is defined. The lymph nodes, stomach, liver, and spleen should not appear enlarged or have defined masses.

While x-rays alone may not definitively diagnose cancer, they provide important information about the location, size, and spread of potential tumors. Accurate interpretation is key to using x-rays effectively in cancer diagnosis and staging.


[Radiographs (X-Rays) for Dogs](

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X-Ray Procedure

dog being positioned for an x-ray

The actual process of taking x-rays of dogs is very similar to taking x-rays of humans. The veterinarian or veterinary technician will bring the dog into the x-ray room and position them appropriately based on the area being imaged. For chest x-rays, the dog will be placed in a standing position with their front and back legs away from their body. For abdominal x-rays, the dog will lay on their back with their legs pulled away to expose the abdomen. The technician will then stand behind a lead shield while x-ray images are taken using an x-ray generator and imaging plate.

Proper positioning is extremely important to ensure the area of interest is clearly visible on the x-ray image. The technician will carefully place the dog and may use sandbags or tape to keep the legs or head from moving during the imaging. Sedation is sometimes required for dogs who cannot stay still. Throughout the procedure, the technician will take radiation safety precautions by wearing a dosimeter badge and utilizing shielding. The x-ray exposure levels are kept as low as possible while still producing diagnostic quality images.

Most x-rays take only a few seconds to obtain the image. The dog usually only needs to stay still for a brief period. For some ill patients, the technician may limit the views taken to shorten anesthesia time if sedation was required. Once the x-rays are complete, the images are digitized and sent to a radiologist for analysis and diagnostic interpretation. The entire appointment usually lasts 10-20 minutes from start to finish.

Limitations of X-Rays

X-rays have some limitations as a diagnostic tool for detecting cancer in dogs, including:

They are not always 100% definitive. Not all tumors show up on X-rays, especially if they are in the early stages. Some cancers may also resemble benign growths on X-rays.

Image quality can be an issue. Subtle changes or small tumors may be missed depending on the clarity of the X-ray image.

There is room for user error. The clarity and usefulness of X-rays depends on the skill and experience of the person taking and interpreting the images. Correct positioning of the dog is also key.

So while X-rays are a useful initial screening, they cannot definitively diagnose cancer in dogs in all cases. Other tests like biopsy, ultrasound, MRI or CT scans may be needed to confirm or provide additional information.

Other Diagnostic Tests

In addition to x-rays, there are other imaging and diagnostic tests that may be used to detect and diagnose cancer in dogs:

CT Scans

a ct scan image

Computed tomography (CT) scans use x-rays and computer technology to create detailed cross-sectional images of the body ( CT scans can visualize tumors in areas like the nasal cavity, lungs, and abdomen more clearly than standard x-rays. However, CT scans require anesthesia and have limited usefulness for lymph nodes and metastases (Hansen, 2019 [1]).


Magnetic resonance imaging (MRI) uses magnetic fields and radio waves to produce detailed 3D images of organs and tissues. MRI provides superior soft tissue detail compared to CT scans and x-rays. It can be useful for brain, spinal cord, bone marrow, and joint evaluations. However, MRI is more expensive, requires longer scan times, and usually involves anesthesia (


Ultrasound uses high-frequency sound waves to create images of organs and masses. It allows real-time visualization and biopsy guidance. Ultrasound is relatively inexpensive and does not require anesthesia. However, image quality depends on the operator’s skill and gas/bone interferes with imaging (Hansen, 2019 [1]).


A biopsy involves removing a sample of tissue and examining it under a microscope. This is the only way to definitively diagnose cancer and determine the tumor type. Biopsies can be done surgically or via needle aspiration. Risks include bleeding and seeding cancer cells along the needle track (

X-Rays for Staging Cancer

X-rays can play an important role in staging cancer in dogs. Staging refers to determining how far the cancer has spread in the body. This helps determine treatment options and prognosis.

One of the main uses of x-rays for cancer staging is evaluating the primary tumor size and looking for metastasis (spread of cancer to other areas of the body). X-rays provide detailed images of bone and can detect bone lesions caused by cancer. They can help determine if a bone tumor has spread to the lungs or other bones.

For example, with bone cancer like osteosarcoma, x-rays of the affected limb can determine the tumor size, location, and bone destruction. Chest x-rays are recommended to check for metastasis to the lungs. Full body x-rays may be done to look for cancer spread to other bones or organs.

Accurate staging is critical for appropriate treatment planning and prognosis determination. While x-rays have limitations, they are widely available and provide an affordable method for initial cancer staging in dogs. Other imaging like CT or MRI scans may be used for more detailed staging when needed.

X-Rays During Cancer Treatment

X-rays can be a very useful tool for monitoring the effectiveness of cancer treatment in dogs. They allow veterinarians to visually assess changes to tumors or cancerous areas before, during, and after treatment. Some key ways x-rays are used during cancer treatment include:

dog's cancer treatment response seen on an x-ray

– Checking if a tumor is responding to chemotherapy or radiation therapy. X-rays give a picture of the size and shape of the tumor, allowing the vet to see if it is shrinking or not.

– Looking for spread or metastasis of cancer to other areas of the body. Unfortunately cancer can sometimes spread during treatment. X-rays of the chest and abdomen can look for signs of metastasis.

– Assessing changes to bones or joints if bone cancer is being treated. Radiation and chemotherapy can sometimes lead to bone tissue damage, which would show on x-rays.

– Monitoring for side effects like pneumonia or intestinal issues. Cancer treatments can increase risk of these complications.

– Tracking implant placement during radiation therapy. Special markers or fiducials are sometimes implanted to help guide and target radiation to tumors.

– Evaluating fractures or other orthopedic issues that may occur during treatment.

Frequent x-rays during cancer treatment are important to help the veterinarian determine if the current protocol is working or if adjustments need to be made. They provide a non-invasive way to visualize the cancer and get an accurate picture of how the dog is responding. X-rays are invaluable imaging tools for monitoring the effectiveness of cancer treatment in canine patients.


In summary, X-rays are one of the most important diagnostic tools for canine lung and other cancers. Chest X-rays can detect primary lung tumors and are the first step in diagnosis. They are also used for staging cancer to determine how far it has spread. During cancer treatment, X-rays help monitor the tumor response and determine if chemotherapy or radiation therapy is working. While X-rays have some limitations, like not detecting small nodules, they provide valuable information about the location, size, and spread of cancer when used along with other tests like CT scans. Given their relative low cost and accessibility, X-rays will continue to be a critical imaging modality for veterinary oncologists and general practitioners alike when evaluating dogs for possible cancer.

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