Sarcoma is a malignant tumor that develops from connective tissue cells. In 90% of dogs, osteosarcoma is diagnosed - a lesion of bone tissue. Veterinary clinics are also contacted regarding neoplasms on the animal’s genitals. Sarcoma in a dog is amenable to palliative treatment, and the animal has a chance of recovery, but only if it is promptly contacted by specialists. More often, neoplasms are mistaken for injuries and inflammatory processes, trying to treat them on their own, which significantly reduces the chances of a positive outcome.
Reasons for tumor development
Malignant neoplasms of the musculoskeletal system in animals account for 4% of all cancers, and in 90% of cases it is osteosarcoma of the paws. The exact causes of the disease are still not known, but even a trivially improperly healed fracture can give rise to the formation of a tumor.
Experts identify embryonic disorders, exposure to chemical carcinogens, radiation exposure and genetic predisposition among the main common causes of the disease. Osteosarcoma is most often diagnosed in Great Danes, Rottweilers, St. Bernards, Moscow Watchdogs, and Irish Setters, with the largest percentage of patients being males.
The age of the animal is also a cause of tumor development. Bone tissue sarcoma is not typical for young dogs; it is a disease of older animals over 6 years of age. Also, small breeds and dogs weighing less than 30 kg do not get osteosarcoma.
Osteosarcoma in dogs
Content
- Primary bone tumors
- Osteosarcoma
- Physical examination
- Diagnosis of osteosarcoma
- Biopsy
- Prognosis and treatment
The current incidence of bone tumors in dogs is approximately 9% of all cancers. Of these, 98% are malignant. Bone tumors can be divided into three groups—primary bone tumors, tumors that metastasize to the bone, and tumors that have invaded the bone from surrounding soft tissue.
Primary bone tumors
The most common bone tumor in dogs is osteosarcoma (OSA). This malignancy accounts for approximately 85% of all primary bone tumors (Brodey & Riser 1969). Other tumors include other sarcomas, e.g. chondrosarcoma (CSA), fibrosarcoma (FSA) and hemangiosarcoma (HSA), which account for approximately 5-10% of all bone tumors. Other rare tumors include lymphosarcoma, plasma cell tumors, osteomas, chondromas, and other sarcomas.
Osteosarcoma
Osteosarcoma is a malignant mesenchymal tumor of primitive bone cells. These cells produce osteoid (matrix), differentiating them from other bone sarcomas. Histologic diagnosis requires a biopsy large enough so that osteosarcoma is not confused with reactive bone, osteomyelitis, chondrosarcoma, hemangiosarcoma, or fibrosarcoma. Osteosarcoma is locally aggressive, causing lysis and/or production of bone and soft tissue and can cause pathological fractures. Osteosarcoma occurs in both the appendicular (peripheral) and axial skeleton. Large dog breeds are considered to be more at risk than small breeds. In fact, 90% of all osteosarcomas occur in dogs weighing more than 20 kg. In most dogs, osteosarcoma develops spontaneously, but it could also be associated with previous trauma, fracture, placement of metal implants and subsequent bone infarctions. The appendicular (peripheral) skeleton accounts for approximately 75% of osteosarcoma cases, and the metaphyseal region of bone is the most common site of tumor. The distal radius and ulna and the distal femur and tibia are the most common sites, accounting for 40% of all osteosarcomas.
Osteosarcoma of the axial skeleton is less common than its appendicular osteosarcoma counterpart and is a common cancer in dogs. Approximately 50% of axial osteosarcomas occur in the bones of the skull, with the greatest distribution noted in the mandible and maxilla. Osteosarcoma of the ribs accounts for 25% of the axial skeleton. Less common are cases of damage to the skull, scapula, vertebrae, pelvic bones and sternum. In small breed dogs (<15 kg), osteosarcoma as a percentage of all skeletal neoplasms is 45%, and 85% in large breeds. Metastatic bone tumors account for approximately 25% of all bone tumors in small dogs, compared with <5% in large dogs.
The following clinical signs that may be observed in dogs with osteosarcoma are signs of intermittent claudication that initially respond to nonsteroidal anti-inflammatory drugs (NSAIDs). In some cases, the appearance of lameness is accompanied by the sudden appearance of a tumor on the limb. Hypertrophic osteopathy can develop in dogs with lung lesions of various origins.
Physical examination
In many cases, the patient will have severe swelling on the affected limb. Depending on the animal, tenderness may not always be present and in some cases there may be significant soft tissue enlargement. Supporting ability can be either unchanged or with severe lameness, which weakly correlates with radiographic signs. Acute lameness with pathological fracture accounts for <3% of all fractures.
Pain may be evoked by deep bony palpation in early cases when soft tissue swelling is not obvious.
Diagnosis of osteosarcoma
Spontaneous unexplained lameness. The presence of a periosteal reaction of a neoplastic nature on an X-ray examination of the affected bone. Osteosarcoma does not affect articular cartilage, although the tumor can spread to soft tissue and adjacent bones. A CT scan (computed tomography), if available, gives a more accurate assessment of the extent of bone involvement.
Differential diagnoses for radiographic aggressive bone lesions include bone tumor (primary or metastatic), infection (fungal or bacterial), and (rarely) bone cysts. Bacterial osteomyelitis is suspected based on history (as infection from surgery or trauma is more common than hematogenous spread). Mycotic osteomyelitis is the main differential diagnosis in countries where fungal diseases are common, as they may be monostotic with a preference for metaphyseal lesions and the spread is hematogenous; however, most mycotic diseases are polyostotic and are associated with pulmonary infiltrates and thoracic lymphadenopathy. The patient's travel history and alarms may indicate a fungal infection.
Clinical diagnosis. Complete blood count and biochemistry and urinalysis are standard. The blood result may be within physiological limits; however, increased alkaline phosphatase (ALKP) levels may occur. It is necessary to take chest x-rays in 3 projections. Less than 10% of dogs with osteosarcoma have visible pulmonary metastases at the time of initial evaluation; however, if present, the prognosis is poor. To identify metastatic lesions (6.4%), diagnostics (CT, MRI) are more effective. The availability of CT means that metastatic lesions not seen on plain radiographs are identified. Although this inevitably influences our discussions with our clients, all data currently available on survival times were obtained from patients diagnosed by radiographs. Our ability to see these lesions should not prevent us from treating patients, but may make it easier to explain the importance of subsequent chemotherapy to the client.
Biopsy
Morphology is necessary for the definitive diagnosis of a bone tumor. The trephine biopsy method is used. Diagnostic accuracy is 82% for a specific tumor type and 92% for differentiating a tumor from other causes, and complications from these procedures are rare. Material for cytology should be performed before fixation in formalin. An open biopsy guarantees a larger biopsy, but with an increased risk of surgical complications (hematoma, infection, tumor seeding, and pathological fracture).
Prognosis and treatment
- Untreated: Severe pain due to extensive destruction of bone and surrounding soft tissue. Euthanasia is the method of choice soon after diagnosis due to pain and/or pathological fracture.
- Analgesics alone: The use of bisphosphonates, NSAIDs, opioids, and other analgesics for medical treatment of the primary tumor still rarely improves 3-month survival.
- Amputation only: Ranges from 119-175 days with a 12-month survival rate of 11-21% and a 24-month survival rate of 0-4%. Death is associated with metastatic disease, usually involving the lungs.
- Amputation or outpatient and adjuvant chemotherapy is 262-540 days with a 12-month survival rate of 33-69%. This depends on the chemotherapy protocol, stage of the disease and location.
The article was prepared by Voronina L.A.,
veterinary therapist “MEDVET” © 2021 SEC “MEDVET”
How the disease develops
The osteogenic form of neoplasms can occur in any bone, but most often (70% of cases) the limbs are affected. The remaining 30% affects the jaw, spine, skull, ribs, but the chest is almost never involved. In the case of paw lesions, tumors form in distal areas with an active growth point.
The tumor appears inside the bone. Tissue destruction proceeds from the center to the periphery with damage to the bone marrow canal. The primary lesion quickly metastasizes, which intensifies the pain syndrome. There are several types of sarcoma in dogs on the paw:
- osteoblastic – damage to bone tissue;
- fibroblastic – damage to the soft tissues of the extremities;
- anaplastic, in which adipose tissue is involved;
- chondroblastic – cartilage tumors;
- fibrous histiocytoma is a lesion of muscle tissue.
What types of this pathology are there?
Like any “self-respecting” cancer, this pathology is divided into types. Here are the most common:
- Damage to the mammary glands in bitches. It often develops if a dog whose puppies died for some reason and developed mastitis does not receive any treatment.
- Transmissible sarcoma. Oddly enough, but it is usually transmitted sexually and is often observed in male dogs used by the “conveyor” method. It is not surprising that this species is often found in the literature as venereal.
- Bone. The most common type, sarcoma is a tumor of connective tissue, and bones are a type of the latter.
- Lymphosarcoma. An extremely dangerous variety, as it can (via the lymphatic system) instantly spread throughout the animal’s entire body.
- Soft fabric. The most poorly studied type. It is assumed that these tumors develop exclusively from metastases.
Symptoms
Often sarcoma in dogs is discovered late, since the process is not immediately visible to the naked eye. The first thing that should alert you is causeless lameness in case of damage to the paws or disruption of the functioning of other parts of the musculoskeletal system (for example, if a tumor develops on the jaw, it will be difficult for the animal to open its mouth and chew food). The pain syndrome in the early stages is mild, so the animal does not show concern and continues to lead its usual lifestyle. The second thing that should alert the owner is frequent fractures. The third obvious sign is the appearance of a tumor. The affected area turns red, swells, and a vascular pattern appears on the skin.
Are some dog breeds more prone to cancer than others?
No, veterinarians around the world do not have such data. There is, however, a hereditary predisposition. It has been noted that if in a particular “family” of dogs, which descends from one or two ancestors, cases of sarcoma are constantly observed, it is better to completely exclude such animals from the reproduction process.
Cancer can occur in any purebred dog, including mongrels, but it is believed that the following breeds are most susceptible to tumors:
- Boxers.
- Great Danes.
- St. Bernards.
- Golden Retrievers.
- Boston Terriers.
Belonging to a certain breed does not mean that a dog will certainly get cancer, but it is at risk and requires more attention to its health.
Diagnostics
The primary method for diagnosing osteosarcoma in a dog is radiography. In case of pronounced pain, x-rays are performed under sedation, which allows you to take pictures from different angles. Radiography allows you to detect the disease in the early stages and determine complications in 10% of cases. In this case, the lesion is clearly visible on the images, the tumor has blurred edges, bone lysis and an increase in bone tissue density are diagnosed.
Radiography in most cases confirms the diagnosis, but morphological examination and biopsy help to clarify the question of the nature of the tumor. It is carried out in closed and open ways. The first is puncture of material from the affected area with needle penetration into the bone marrow space. In this way, it is determined how much the tumor has metastasized. The open method allows you to take a large amount of material and determine the morphological identity of the tumor, i.e. make an accurate diagnosis.
The dog's blood is drawn regularly. In case of malignant tumors, its formula contains increased leukocytes and alkaline phosphatase, which indicates the progression of the tumor and its metastasis in distant areas. During diagnosis, it is necessary to differentiate the neoplasm from postoperative osteomyelitis, fungal infection of bone tissue, and the presence of cysts.
Treatment
Treatment of cancer patients is almost the same for both people and animals. It is always complex and consists of the following stages:
- Surgical removal of the tumor. The neoplasm must be removed with a part of healthy tissue in order to protect against possible penetration of cancer cells into surrounding tissues and spread of the process.
- Irradiation using a special device. This is not possible in all veterinary clinics. The method is not used for all types of cancer tumors and is not applicable for some types of tumor localization.
- Chemotherapy. It involves taking toxic drugs that can kill cancer cells, destroy or reduce tumors and metastases, and also prevent their formation and further spread.
You cannot give your dog medications intended for humans, since, despite the general principles of the effect on tumors, the type of medication, dosage and intensity of treatment can only be selected by a veterinarian. This is because the dose is calculated only for the individual dog, taking into account his weight, age, general health and the presence of additional problems.
If the doctor prescribes painkillers, there is also a danger of overdose. Owners should obtain full advice from a specialist on how they should act in certain situations.
Treatment of any form of cancer is extremely complex, lengthy and expensive. However, there are some types of this terrible disease that are easier to treat than others and can be cured completely or give long-term remission. These include skin cancer in the early stages.
Chemotherapy is often used to treat osteosarcoma along with surgery to prevent the disease from spreading to other parts of the dog's body, especially the lymph nodes. In severe cases, the veterinarian may recommend amputation of the limb to completely remove the tumor.
Possible complications
With cancer, the most dangerous complication is metastases, leading to the spread of cancer throughout the dog’s body. This leads to a generalization of the process, which is expressed by increased intoxication. If organs such as the brain, lungs, liver and, less commonly, the heart are affected, the dog’s fate is predetermined. The duration of her remaining life is calculated in months, and sometimes weeks.
Bone lesions lead to pathological fractures that do not heal. Problems with the digestive system are extremely exhausting for both the dog and its owners. She literally melts before our eyes, practically dying from exhaustion.
Since cancer is treatable only in the first two stages, in the presence of terminal stages there is no talk of recovery. You can only provide your pet with a calm, painless last days of life, surrounded by loving and caring owners.
Why is a cancerous tumor on the paw dangerous?
Any malignant neoplasm poses a threat to the pet's life. The danger of a cancerous tumor on the paw is that very often the correct diagnosis is made already in the later stages, when treatment may not bring the desired result.
This is because many dogs do not show signs of illness, and the owner may not see them in a timely manner. At the stage when the animal becomes weakened and its temperature rises, the cancer cells are already growing significantly, and metastases appear in the internal organs.
At this stage, treatment may not bring results, and the pet dies after a few weeks or months.
What therapy can be used for canine oncology?
Oncology is a medical discipline that studies tumors (both benign and malignant), studies the causes of their appearance, the mechanisms and patterns of their development, their prevention, diagnosis and treatment.
A tumor, or neoplasm (neoplasia, neoplasm) is a group of cells of newly formed tissue in which the processes of growth, differentiation and cell reproduction are disrupted. The body's control over these processes is lost. The main features of tumor tissue are tissue or cellular atypia, progression, relative autonomy and unlimited growth.
Metastasis is the process of tumor cells spreading in the body to other organs in various ways: with the blood or lymph flow, contact (into adjacent tissues), along nerve bundles. As a result of this process, secondary foci are formed - metastases, which, as a rule, grow faster than the primary tumor.
If there is any possibility of a successful outcome, it is better to immediately agree to surgery, which is the most common treatment for any type of tumor. A tumor that has been properly removed will not grow back, but one that is simply suppressed by chemotherapy can have a sudden relapse. Chemotherapy is also often used in treatment, but should not be relied upon alone in this case.
