One of the most feared diseases is osteosarcoma in dogs. Osteosarcomas are malignant type tumors that can develop in dogs with very high metastatic potential. All this makes an early diagnosis necessary to detect and treat it in time.
When your dog presents lameness, inflammation and pain at the level of the metaphysis of long bones, you should check with your veterinarian to rule out the possibility of the early development of a tumor.
Generally, dogs that suffer from this type of tumor do not have a good prognosis because their life expectancy is noticeably shortened.
Although it also largely depends on whether there is a presence of metastasis and how advanced its evolution is. My previous dog, Nit, died of osteosarcoma in his hind leg bone with metastases.
It was so fast that we only had time to do the tests and know the diagnosis once he died. We euthanized him because his pain was unbearable, and he was already almost 15 years old.
So that you do not find yourself alone in this situation, I have tried to explain everything about osteosarcoma in dogs in the simplest way.
You will read many technicalities, but I think it is important to mention them because they are the same ones that your veterinarian will use in case you are diagnosed with osteosarcoma.
What is Osteosarcoma in Dogs?
It is the development of primary-type tumors in the bones, very common among dogs, reaching 85% of the cases of bone tumors presented.
75% of the time, they occur in the appendicular skeleton (includes all the bones that make up the upper and lower limbs, including the pelvis) rather than in the axial skeleton (25% of cases); on average.
Among other primary neoplasms affecting the bones are chondrosarcoma, hemangiosarcoma, fibrosarcoma, multilobular osteochondrosarcoma and histiocytic sarcoma.
On certain occasions, certain bone lesions can be observed that are related to non-primary tumors that affect the bones (being malignant) in the form of metastases.
These are most frequently present in urothelial, mammary or even prostate carcinomas. They can also present as part of the systemic process, as are the cases of lymphoma, multiple myeloma and disseminated malignant histiocytosis.
This type of osteosarcoma is a mesenchymal tumor that occurs in the primitive bone cells of the dog. This condition usually occurs in large or giant dogs, with cases in which it occurs in small breeds being rare.
The distribution in which this type of tumor usually develops is in the longest bones, such as the proximal humerus, distal femur, distal radius and proximal tibia.
These manage to affect the front extremities with a ratio of 2 to 1 of the cases presented on average. When it comes to tumor development in the axial skeleton, it is usually found that most cases develop in the mandible, cranial bones, ribs, maxillae, pelvis and nasal cavities.
Sometimes, it can develop in tissues outside the bone, such as in the mammary glands.
Origin of Osteosarcoma in Dogs
The etiological study of sarcoma has not been able to determine the possible origins or causes of tumor development accurately. In this sense, hypothetical viral-type causes have been proposed that have not yet been consistently demonstrated.
Similarly, other causes may be physical factors, such as metal implants, microtrauma, exposure to ionizing radiation or fracture welding without proper internal resolution.
Even molecular and genetic origins, in which there is a certain idea that the tendency to develop tumors may be hereditary.
Note: A greater development has been observed in both male and female specimens, although in the case of Rottweilers, there seems to be an inversely proportional trend between the risk of developing osteosarcoma and the time of exposure to gonadal hormones.
Osteosarcoma in Dogs Symptoms
- Lameness is usually the most common symptom and can occur suddenly or gradually, depending on the case. It usually occurs when taking anti-inflammatory treatments, although it reappears when stopped.
- Local inflammation: This inflammation is usually caused by the tumor itself.
- Bone pain: It can occur due to microfractures of the bones involved or also caused by disruption of the periosteum due to osteolysis of the cortical bone. This is due to the extension of the tumor through the spinal canal.
- Fever: The presence of fever could occur due to the dog’s body’s immune response to tumor formation.
- Lack of appetite: It can happen that the tumor presses on the stomach and other digestive organs, causing dysfunction that leads to a slowdown in digestion. It could even completely block the stomach and intestines.
- Apathy: The development of a tumor consumes a lot of energy from the dog, which can lead to low activity levels.
- Pain: They are caused by low blood flow to the extremities due to inflammation due to the presence of the tumor because they cut off blood flow. It usually presents chronically.
Note: It is important to note that these symptoms usually appear in the presence of osteosarcoma. However, they are not exclusive to this condition and may be caused by other factors.
Therefore, it is recommended that the adopter, in case of noticing any or all of them, go to the veterinarian so that they can do the appropriate tests. The haste is important, aiming for your pet to have a correct diagnosis and determine the appropriate treatment.
How is Canine Osteosarcoma Diagnosed?
When the symptoms mentioned above have been observed, the dog should be taken to the veterinarian so that he can do a thorough and specialized evaluation.
This normally consists of taking X-rays of the dog, in which if there are signs of any sign that indicates the possible presence of sarcoma, it will be necessary to perform a biopsy through a bone sample.
The sample must then be further analyzed in the laboratory.
In the latter case, complete blood count (CBC) blood tests, biochemical profiles and urinalysis are performed that provide basic information that guides the veterinarian in his diagnosis, even determining if chemotherapy is necessary.
This disease consists of 3 stages of development that are classified by the TNM system (being the acronym for Tumor T, Lymph Node N and Metastasis M)
In this way, we have three types of exploratory processes to determine and certify the presence of tumors:
Simple radiography is about the examination through x-ray plates of the appendicular skeleton in 2 positions and 3 when it comes to metastases in the lungs or other areas.
This is the basis on which the diagnosis starts. The lesions are usually shown as monostotic, presenting aggressiveness when found in the bones. Due to bone lysis, pathological fractures may occur in some individuals.
The so-called Codman’s triangle is usually present, although it is not definitively indicative of the presence of osteosarcoma.
The mediolateral radiograph is normally taken from the left hind limb of the animal with the presence of femoral osteosarcoma, and lytic areas can be seen in the discontinuous distal femoral diaphysis of the periosteum, generally associated with amorphous periosteal reaction.
Radiological studies are recommended due to the high rate of presence of metastases. If possible, it is recommended to perform a chest CT to study the possible tumor lesions present.
Nuclear scintigraphy is the best technique used due to its degree of sensitivity and precision.
Although the medical history, clinical picture and radiological examinations make a presumptive diagnosis possible, evaluating and ruling out other possible causes of lytic or proliferative bone lesions is also necessary.
Cytology and Biopsy
Cytology consists of tissue analysis by aspirating them with a fine needle stained with alkaline phosphate. This procedure is minimally invasive.
A bone biopsy is usually performed when it is located in unusual or accessible sites or is an atypical lesion. If a surgical procedure removes the tumor, histopathologic confirmation of osteosarcoma is necessary.
In cases of bone tumors, the sample should be taken directly from the center of the lesion since, contrary to what happens with soft tissue tumors, samples taken from the periphery might not be diagnostic.
A complementary physical examination is necessary. For this, orthopedic and neurological tests are carried out, especially if the possibility of limb amputation is estimated.
In addition, a hematological, serum biochemical and urinalysis evaluation is highly recommended. The diagnosis begins by observing the patient at rest to determine the exact site where the injury occurs by reacting to pain with special palpation in the area of the metaphysis of the bones, deformity and edema.
When it is observed in movement, it is done to evaluate whether there is a loss of functionality and its degree, as well as the presence and severity of claudication.
Tumor metastasis occurs primarily by the hematogenous route (through the blood), targeting mainly the lungs and other bones, although regional lymph node metastases have been detected in more than 37% of dogs with OSA.
Most cases (exceeding 90% of incidences) present micrometastases, although less than 15% of dogs usually present detectable cases in the initial diagnosis.
Osteosarcoma in Dogs Treatment
There are various techniques and procedures with which to treat canine osteosarcoma. Next, we will list some of them:
With a Surgery
One of the first options for treatment is surgery: with it, the amputation of the affected limb is sought. Most dogs can achieve a good quality of life after surgery.
However, the previous orthopedic or neurological difficulties that could generate later complications must be considered.
The total amputation of the limb is not usually recommended when it is observed that there is already the presence of tumor metastases or if the dog has previous mobility problems in which the rest of the limbs are involved.
This would deteriorate and prevent a faster and more satisfactory recovery.
Intervention, Removal and Reconstruction
The most suitable patients for this type of surgery are those with the tumor located in the distal radius or ulna areas, without any macroscopic disease evident elsewhere.
Also, those who do not have other diseases and the tumor is less than half the size of the radius. In addition, dogs that have pathological fractures or tumors infiltrated in the circumference of the limb’s soft tissues or other edematous lesions since the risk they run is very high compared to the benefit they can obtain.
This therapy consists of administering cytotoxic drugs (chemotherapy) as they contribute to increasing the survival period. The most widely used are cisplatin, carboplatin and doxorubicin, although the former is hardly used anymore due to the side effects it usually causes.
However, it has not been conclusively proven that any of these is superior in efficacy or that their combination is more effective.
In the same way, no differences have been recorded regarding the survival rate between dogs receiving preoperative or intraoperative chemotherapy treatment or even those receiving it up to 3 weeks after the intervention.
Therefore, the choice of drug will depend on the particular circumstances of each case, considering possible adverse consequences, side effects and treatment costs.
Pain Treatment and Management
One of the most important treatments consists of treating and managing the pain caused by osteosarcoma in the dog because the bone destruction caused by it produces truly unbearable pain.
It begins with the application of non-steroidal anti-inflammatory drugs and opiates, but if this is not enough, other substances such as gabapentin, bisphosphonates and amantadine are administered.
Although they are not analgesics per se, they act by inhibiting bone resorption and increasing its density.
It is also hypofractionated, or palliative radiation considered the most effective therapy for rapid pain control while helping slow down the disease’s progress.