Happy spring doctor! Hoping you enjoyed your break. If your time permits, I was wondering if you could give us layman’s run down on the Bad News of bone cancers? And perhaps link your quality of life post because I can’t seem to find it. Thank you from the dog who’s going for a CT and bone biopsy next week. Question tax: do you like gingerbread cookies?
If you are feeling up to the Bad News that is the neoplasia (cancers) found in bones of dogs, fair warning it is pretty bad news overall. Some are distinctly worse than others, but because of their location tumors of the bone present some particular challenges.From a diagnostic standpoint, you can’t perform a Fine Needle Aspirate on a bone tumor very easily. A fine needle just doesn’t cut it if you have to go through bone, you need a serious bone biopsy with a special needle and that generally can’t be processed quickly and easily in the clinic, it must go to a lab for decalcification (removing the calcium is why bone samples take so long to process) and analysis. You also generally can’t ultrasound them well, as ultrasound does not penetrate the bone, so may be limited to X rays, CT scans (we don’t call them CAT scans in vet medicine because that’s just confusing) and surgical biopsies. When we talk about cancers, we often use the ending ‘sarcoma’ or ‘carcinoma’ to indicate an aggressive malignancy, and just ‘oma’ to indicate a benign one, eg a Lipoma is benign and doesn’t invade or spread, but a Liposarcoma is bad news. The exception to this is tumors arising from white blood cell lines (eg lymphoma) and melanoma, which are essentially all malignant.
The benign variants of a cancer maybe a case of ‘cut it out and you are done’, the difficulty is in how to cut out enough bone and still retain function.
Types of Bone Cancers in Dogs
We can see tumors within bones develop from any of the cell types we find there:
Osteosarcomas (85%) and Osteomas - from bone producing cells
Chondrosarcoma and Chondroma - from cartilage
Fibrosarcoma and Fibroma - from fibrous connective tissue
Multiple myeloma - from bone marrow
Leukemia - from bone marrow
Histiocytic sarcoma - from a type of white blood cell
Haemangiosarcoma - from blood vessel lining
Osteoclastoma - from bone dissolving cells
Metastatic cancer from elsewhere in the body which has lodged in the bone, eg melanoma, anal gland adenocarcinoma, mammary carcinoma
And these cancers may look different depending on whether they arise from the medulla (the inside, where the bone marrow is), the cortex (the outer, thick part) or the periosteum (the very outside).
The overwhelming majority of bone cancers in dogs are osteosarcoma. In little dogs they tend to occur in the skull, ribs and spine. In big dogs they are more common in the limbs, classically shoulder, wrist and knee (“away from the elbow and towards the knee”) but they can occur anywhere. With amputation, removing the primary cancer and the associated pain, dogs will average about 6 months survival time. Without amputation it’s more like two. Some whizz bang surgeons can offer limb sparing surgery in some cases, where the relevant bone is basically replaced by a metal tube with similar survival times. With surgery and chemo dogs can be expected to make a year, with some (20% or so last time I looked) potentially making it to three years, which was when the study ended. Osteosarcoma likes to spread to lung, and some dogs also received a partial lung lobectomy before chemo to remove known a metastasis. This is why a full body CT scan is often recommended.
Osteosarcoma, in addition to very common locations, also has a fairly distinctive radiographic appearance. Most begin in the medullary cavity (inside) of the bone and work their way out, dissolving building new bone as they go. These lesions on Xray are both destructive and proliferative. If we think it’s an OSarc, it probably is.Without surgery, dogs are at risk of a pathologic fracture, where the cancer has eaten away at so much bone that it spontaneously breaks. They are very bad news, and we are talking about surviving only months, depending on pain control.
Chondrosarcoma behave in a very similar manner to osteosarcoma, but do not produce as much new bone. They are also highly aggressive.
Fibrosarcomas can invade bone from the outside, or arise from within it, from connective tissue. They may be well differentiated, which usually means they are closer to normal tissue and slower to spread, or anaplastic, which means they are so weird you can barely identify them and anything goes.
Liposarcomas usually develop from within the bone marrow and kind of eat their way out. Haemangiosarcoma also develops from within the bone marrow, usually at either end of the long bones, and can cause swelling in addition to pain and lameness, this type of tumor often causes pathological fractures. These tumors can be kind of difficult to see, especially in early cases.
Histiocytic sarcoma, leukemia and multiple myeloma are tumors arising from the bone marrow which may have systemic effects. Multiple myeloma produces a ‘moth eaten’ appearance and likes the pelvis for some reason. These often have systemic effects and are usually treated medically rather than surgically.
Osteoclastoma is a weird one, and there have not been many cases reported of this cancer developing from bone dissolving cells. They are usually lytic and unstable, but I don’t know much about them.
While malignant tumors of the bone often spread to the lungs, cancer originating from other sites can spread to bones (metastasis) and cause unpredictable lesions, commonly mammary gland cancer and anal gland adenocarcinoma, but melanoma and a few others can do it too. You can also get Mast Cell Tumors in the bone marrow, as it has a really good blood supply.
There is also all the non-malignant versions of all the above types of neoplasia, which do not spread but can still grow, causing disruption and pain.
Unfortunately you need cells under a microscope to know for certain what we are dealing with, but sometimes we make our decisions based on the dog’s comfort without them.
Some of the Quality of Life posts, because I’m not sure which one you are after:
Quality of Life with the graph
Best wishes for you and Thistle this week.
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