Depending on the chosen treatment and tumor location
Bone tumors usually occur at the bones of the limbs (average of 75%). It is known that this tumor type appears twice as much on the front limb than the hind limb and has a preferential location per bone. Twenty-five % of bone tumors appear at the skull and spine (27% at the lower jaw, 22% the upper jaw, 15% spine, 14% skull, 10% ribs, 9% nasal cavity/sinus near the nose, 6% hip bones). Although rare, bone tumors can also be found in mammary glands, subcutaneous tissue, spleen, intestines, liver, kidney, testicle, vagina, eye, stomach ligament, the delineation of the articulation (synovium), meninges, adrenals.
Osteosarcomas are very aggressive tumors. They have locally a very invasive behavior and cause bone loss and/or produce inferior bone. Where the tumor is located, there is usually a visible swelling of the tissue. Because the tumor can locally damage the bone, this process could lead to a spontaneous fracture of that bone.
Metastases are very common and develop early during the course of the disease, although they usually don’t cause any symptoms and therefore go unnoticed (= subclinical). Although at the time of diagnosis less than 15% of dogs will show detectable metastases on radiographs, about 90% of dogs dies within one year with metastases in the lungs (when treatment was limited to surgery). This tumor type metastasizes usually via the blood, but in rare cases it can also be found in the local lymph nodes. The lungs are the most reported location for metastases, followed by spreading towards the bones or soft tissues.
This tumor type is most prevalent in average age to older dogs (median of 7 years), but it has been reported in young (1-2 year old) dogs as well.
A higher risk for development of this tumor type was reported for large and giant races (Saint-Bernard, Danish Dog, Irish Setter, Dobermann, Rottweiler, German shepherd, Golden retriever). As a general rule, large dogs have a greater risk of developing on bone tumor on the limbs, whereas smaller dogs, a greater risk of developing one in (the extension of) the spine (= axial skeleton).
To be more precise:
Dogs with a weight above 40 kg represent 29% of the dog population with bone tumors. In these dogs, only 5% of bone tumors occurs at the skull or spine (axial skeleton).
Dogs weighing less than 15 kg represent 5% of the canine population with bone tumors. In these dogs, 59% of the tumors are localized to the skull and the spine.
The symptoms depend on the tumor location. If an osteosarcoma is situated on a limb, there will be a local swelling that can be painful and lead to limping. If it’s situated on the axial skeleton, the symptoms can vary and include a local swelling with or without limping, difficulties eating (if in the upper or lower jaw), mild protrusion of the eye and being painful when the mouth is opened (if in the orbit and the lower jaw), facial deformation and nasal discharge (if in the sinus and nasal cavity), being overly sensitive with or without neurological symptoms (if in the spine). Respiratory problems rarely occur, even if radiographs of the chest clearly show the presence of metastases.
Furthermore, a lower energy level can occur and the occurrence of an increased level of calcium in the blood (hypercalcemia) is very rare.
Via radiographs, much information can be collected about the presence of a bone tumor. In case of osteosarcomas, bone destruction is expected to be seen on the radiograph, as well as an uncoordinated bone production because of the irritation of the bone membrane. However, when the disease is in a very early stage, it isn’t always easy to track down these lesions and then a CT-scan can be of more use.
Via a biopsy, the type of bone tumor can be confirmed. Via scintigraphy and aspirates of (local) lymph nodes, the veterinarian can visualize the distribution of the osteosarcoma. Other options to map the tumor distribution include a combination of radiographs and/or CT scan, ultrasound of the abdomen to detect metastases towards the lymph nodes and internal organs.
Some blood values can indicate an increased bone activity.
The treatment option depends on the location of the tumor and the presence of metastases. Furthermore, an osteosarcoma can be a very painful tumor because of the irritation of the bone membrane, which requires appropriate painkilling. The more treatments (surgery, chemotherapy, radiotherapy) are combined, the higher the chances of success. This because osteosarcomas often require local (surgery, radiotherapy) as well as general (chemotherapy) treatment (in case of metastases).
If possible, the veterinarian will surgically remove the tumor. This is relatively simple for osteosarcomas of the limbs, but less obvious for tumors of the skull or spine. When the tumor causes pain due to its size and location at the spine, a part of it can be removed (decompression) to make life more comfortable for the dog. Generally speaking, surgical removal of a tumor on the limb leads to amputation of the paw. In certain cases, limb-sparing surgery can be considered, but this is a complex procedure requiring a team of veterinarians. Amputation of the limb is an option for large dogs if the remaining 3 paws are healthy (e.g. do not harbor advanced arthrosis).
Metastases can be surgically removed to somewhat prolong life or to improve the quality of life for dogs in whom -as a consequence of metastases towards the lungs- hypertrophic osteopathy occurs (abnormal widening of the bone as a result of new bone production). When the metastases are removed, the symptoms associated with hypertrophic osteopathy disappear as well.
These images show the preservation of a good quality of life after paw amputation.
Even when no metastases were detected at the time of diagnosis, it is advised to proceed with chemotherapy after surgery because this tumor type metastasizes very frequently. At this time, chemotherapy isn’t very satisfactory in the treatment of metastases. Presumably, this is due to the limited access/distribution of this medication within the tumor and metastases. This approach will possibly become more important in the future when it can be combined with medication that enhances the access to the tumor and metastases.
Receptor tyrosine kinase inhibitors such as Masivet® and Palladia® are tablets that can be administered orally and block growth receptors within the tumor. As with chemotherapy, receptor tyrosine kinase inhibitors only work well when they can efficiently be distributed within the tumor. So far, this treatment has not led to a cure, but a slowdown of the growth was seen with half of the tested dogs (on a total of 23).
Radiotherapy (at higher doses) is often combined with limb-sparing surgery and done prior to surgery. High doses can also be used to cause necrosis within the tumor when the tumor’s location does not allow a surgical removal. In general, radiotherapy can contribute to the temporary control of the tumor growth.
Radio-isotopes are compounds capable of specifically binding bone cells. When bound to the bone cell, they will emit alpha or beta particles that locally kill the cancer cells. 153Sm-EDTMP is a bone-seeking isotope that is used to treat primary and metastasized bone tumors as it is preferentially absorbed by the bone cancer cells. The treatment consists of intravenous administration of the isotope, after which it binds on the bone.
Overall, this treatment will not lead to a cure, but rather a prolongation of life. Depending the situation and/or treatment, the dog’s life can be extended for months to even years.
Good pain relief depends on the patient and his affliction. In case of osteosarcomas, different stages and forms of pain can be experienced.
Initially (local) anti-inflammatory drugs can be sufficient. When the tumor grows, nerve tissue can become involved and may require the need of pain relief such as morphine-based drugs used for other pain levels (such as nerve pain). When the tumor starts to grow uncontrollably and destroys bone, bone protection such as aminobiphosphonates can be added to the pain relief plan (aminobiphosphonates is used as treatment against bone destruction, such as metastases to bones in men).
Radiotherapy is one of the most efficient treatment options for the relief of pain caused by bone destruction in humans with cancer. This technique is also used to temporarily stun the tumor growth and thus reduce bone pain (the latter is the case for 74-93% of dogs with bone cancer). The relief is temporary and remains effective between 53 and 103 days.
Radiopharmaceuticals are an option as well, although more information needs to be gathered on its use in dogs with metastasized bone tumors. Radiopharmaceuticals consist of radio-isotopes that emit local radiation and thus temporarily control the tumor. This pain relief technique is successfully used in humans with metastasized bone tumors.
The mental health of the dog is a factor that should not be underestimated: offering continued attention and love, can reduce feelings of pain in humans and animals. It’s important to avoid boredom, fatigue and isolation in your dog, as this lowers the pain threshold. A regular scheme and environment, sufficient sleep/rest, environmental enrichment, company, sympathy and avoiding unpleasant environments can considerably decrease the inconvenience associated with cancer.
The prognosis depends on the chosen treatment and tumor location.
Palliative pain relief: a 2.5 months survival can be expected.
Radiotherapy: survival of 4 months.
Limb amputation: survival of 4.3 months; 12% of dogs will still be alive after 1 year; 2% after 2 years.
Limb amputation and chemotherapy: depending on the metastases a survival of 10-11 months can be expected; 35-50% of dogs will still be alive after 1 year, 20-28% after 2 years.
Osteosarcomas of the skull/lower or upper jaw are locally aggressive but metastasize less than an osteosarcoma on the limb (37%).
Pre-operative high blood levels of alkaline phosphatase are associated with a shorter survival.
There are no pictures available for this tumor type
Ehrhart NP, Ryan SD, Fan TM. Tumor of the Skeletal System. Withrow and MacEwen's Small Animal Clinical Oncology, 5th edition, Chapter 24 (p 463-490).
With the kind contribution of Prof. dr. Paul Simoens, Vakgroep Morfologie, Faculty of Veterinary Medicine, UGent for the anatomical representations.
With the kind contribution of the Imaging Department of Companion Animals, Faculty of Veterinary Medicine, UGent for the radiograph images
Service of Cancerology, VetAgro Sup, Campus veterinary medicine Lyon, France