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Rib Bone Cancer in Dogs

Dog with Rib Bone Cancer

Rib bone cancer in dogs is not as common as bone cancer affecting the legs, but nevertheless remains a worrisome condition. There are two most common specific bone rib tumors affecting dogs, namely, osteosarcoma and chondrosarcoma. Both these cancers are known for causing the presence of a hard mass on the chest wall, where the ribs are located. Along with the presence of a mass on the dog's ribs, affected dogs may show other signs as well such as trouble breathing or lameness if the growth is found on the first ribs. Quick diagnosis of rib bone cancer in dogs is important so to increase survival times. Prognosis in certain types of rib bone cancer in dogs may be poor once the cancer has advanced to involve the lungs.

dog rib anATOMY

Rib Bones in Dogs

Dogs are equipped with 13 pairs of ribs (for a total of 26). Ribs are those long curved bones that compose the rib cage giving the dog's abdomen its typical barrel-shape. The ribs serve an important function: to help protect the dog's lungs, heart, and other internal organs keeping them well contained in the abdomen.

At the top, the dog's ribs attach to the dog's vertebral column (the spine). The ribs then spring away in a wide arch and attach at the bottom to the dog's sternum (breastbone).

The first set of ribs that attach directly to the dog's breastbone are known as "true ribs" while those that do not directly attach are known as "false ribs." Interestingly, unlike the rest of the dog's ribs, the cartilage of a dog's last rib doesn't connect to anything at all and is therefore called a "floating rib" as seen in the picture of the left.

At times, people feel a "lump" on the dog's last rib when in reality what they are feeling is the edge of " a dog's floating rib" along the flank.

According to a study, cancer of the ribs in dogs showed to affect mostly ribs 5 through 9 with the right side affected twice as often as the left side.

Rib Bone Cancer in Dogs due to Osteosarcoma

rib bone cancer in dogs

It is estimated that 80 percent of primary bone cancers in dogs are osteosarcomas, which represent 2 to 7 percent of all types of dog cancer. Osteosarcoma is primarily a cancer of middle-aged to older dogs, but younger dogs can also be affected. Large to giant breed dogs are more predisposed and generally male dogs are more affected than females.

Statistically, more than 75 percent of osteosarcomas affect the long bones, with the front legs affected twice as likely than the rear legs. The remainder occur on the dog's axial skeleton (head and trunk areas) and that includes the dog's upper and lower jaw,the spine, nasal cavity, pelvic area and the dog's ribs.

Osteosarcoma of the ribs in dogs is commonly found at the costochondral junction, that is, the area where the ribs merge with the sternum (breastbone) in the location depicted in the picture on the right.

Symptoms suggesting osteosarcoma of the dog's ribs include local swelling due the presence of a bone-forming tumor. Along with the swelling, respiratory compromise may result as a result of the cancer compressing the lungs or due to metastasis.

" The most common locations for OSA (osteosarcoma) in the axial skeleton are the mandible and maxilla followed by the spine, cranium, ribs, nasal cavity and pelvis."~Heather M. Wilson , veterinary oncologist

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Rib Bone Cancer Due to Chondrosarcoma

It is estimated that dog bone cancers other than osteosarcoma account to about 20 percent. Chondrosarcomas are the second most common type of bone cancer and represent up to 10 percent of all types of dog bone cancers. This type of cancer affects mostly large dog breeds, with giant breeds less commonly affected. It can affect dogs of any age, but it's more commonly found in middle-aged dogs.

Chondrosarcomas have a preference for flat bones such as nasal bones, ribs, jaw bones and pelvic bones. When this bone cancer affects the dog's ribs, it presents as a firm swelling at the costochondral junction, that is, the area where the ribs merge with the sternum (breastbone) in the location depicted in the picture above on the right. As in the case of osteosarcoma, chondrosarcomas of the dog's ribs can lead to respiratory compromise as the growth expands.

"Some dogs with chondrosarcoma live a few months, others live a few years. The rib tumors are usually not obviously painful, but can lead to lung compression if they grow inward."~Dr. Anne, veterinarian

Rib Bone Cancer Due to Fibrosarcoma 

It is estimated that fibrosarcomas represent about 7 percent of all primary bone cancers. This condition affects mostly older dogs and the axial skeleton (head and torso) is more likely to be affected compared to the appendicular skeleton (limbs). Fibrosarcoma i composed by fibrous collagen material.

Fibrosarcoma in dogs usually originates in the soft tissue but in some rare cases, at times a fibrosarcoma tumor may originate in the bone. It's important to therefore distinguish this type of cancer from fibrosarcoma of soft tissue origin, which may invade nearby bony structures, leading to weakening of the bone.

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Rib Bone Cancer Due to Hemangiosarcoma

It is estimated that hemangiosarcomas represent 2 to 3 percent of the different types of primary bone cancers affecting dogs. This condition affects mostly middle-aged dogs but can affect any dog of any age. Male dogs are more predisposed than females. Breeds commonly affected by this type of cancer include boxers, great danes and German shepherds.

Hemangiosarcomas have a predisposition to more likely affect the dog's axial skeleton (head and trunk areas). It is estimated that 57 percent of hemangiosarcomas affect the dog's axial skeleton (head and trunk areas) while 43 percent affect the dog's appendicular skeleton (limbs). When this cancer affects the dog's axial skeleton, the preferred area is the rib area.

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Like osteosarcoma, this form of cancer has a great tendency to spread, with an estimated 100 percent of dogs developing spread of cancer within 1 year. Spread may occur to the dog's lungs, liver, kidneys, heart, omentum, and peritoneum. Symptoms of hemangiosarcoma of the dog's rib are similar to those of osteosarcoma.

According to a study on rib bone cancer in dogs, "Fifty-four dogs with primary tumors of the rib were evaluated. Thirty-four dogs had osteosarcomas, 15 dogs had chondrosarcomas, three dogs had hemangiosarcomas, and two dogs had fibrosarcomas."

At the Vet's Office

The tissue sample taken from the liver is checked under a microscope.

A biopsy is the most accurate diagnostic tool for rib bone cancer in dogs

A dog with a lump on the ribs should be evaluated by a vet to rule out any possible tumors to the dog's skeletal system. The vet will likely ask several questions in regards to the dog's symptoms. How long has the swelling been there? Is the dog active, has a good appetite? Does the dog seem to have any pain? Any breathing problems?

Next, the vet will likely perform a physical examination and take a look at the localized swelling. X-rays are often taken, generally two views of the site. X-rays are insightful as bone cancers easily show on x-rays. The vet will look for specific signs such as destruction of bone (lysis) and bony proliferation.

Chest x-rays are often done to check for signs of the cancer spreading to the lungs. Signs of spread to the lungs are usually not seen until the nodules are larger than 6 to 8 mm.

A complete blood count, biochemistry profile and urinalysis is also important so to have an insight on the dog's overall physical condition. A CT scan may be recommended. All these tests should help confirm or rule out rib bone cancer in dogs.

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Differentiating the various types of rib bone cancer in dogs can be challenging at times. Definite diagnosis requires bone biopsy (done via biopsy needle with the dog sedated) followed by histological evaluation.

Treatment depends on the type of rib bone cancer in dogs cancer that is found. Surgical removal of the mass and rib bone/bones that are affected is usually suggested.

dog grooming back

Prognosis of Rib Bone Cancer in Dogs 

Prognosis of rib bone cancer in dogs depends on the type of cancer. As seen, osteosarcoma is the most prevalent type of bone cancer (80 percent), followed by chondrosarcoma (20 percent) and then fibrosarcoma (7 percent) followed by hemangiosarcoma (2-3 percent). Other bone tumors are much rarer and these include synovial cell sarcomas, giant cell tumors, myelomas and lymphosarcomas.

Osteosarcoma of the ribs has in general a poor prognosis. According to a study, less than 10 percent of affected dogs survived more than 4 months after being diagnosed. Dogs receiving chemo along with surgery though had a longer median survival time (240 days), compared to dogs with rib osteosarcoma treated by surgery alone (median survival, 90 days).

Prognosis of rib bone chondrosarcoma has a better prognosis considering that this form of cancer has a tendency to be less likely to spread to the lungs or other organs compared to osteosarcomas. A study has shown the metastatic rate of chondrosarcomas to be around 17 percent. These cancers have been successfully removed by rib and chest wall surgical removal. Response to chemo or radiation appears poor.

Prognosis of fibrosarcoma varies, it appears that it has a a better prognosis than osteosarcoma considering that this cancer is less likely to spread, but the prognosis of chondrosarcoma was more favorable according to a stud. However, in some isolated cases, there have been instances of this cancer spreading throughout the body, affecting organs, lymph nodes and skin.

Hemangiosarcoma has a poor prognosis. Lesions affecting the axial skeleton, including ribs are not controlled much by surgery.

"Chondrosarcoma had a better prognosis (median disease-free interval, 1,080 days; median survival, 1,080 days) than osteosarcoma, hemangiosarcoma, or fibrosarcoma of the rib." ~Source J Am Anim Hosp Assoc. 1995 Jan-Feb;31(1):65-9., Primary rib tumors in 54 dogs.

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  • J Am Vet Med Assoc. 1982 Apr 15;180(8):927-33. Malignant neoplasia of canine ribs: clinical, radiographic, and pathologic findings. Feeney DA, Johnston GR, Grindem CB, Toombs JP, Caywood DD, Hanlon GF.
  • J Am Anim Hosp Assoc. 1995 Jan-Feb;31(1):65-9.Primary rib tumors in 54 dogs.

    Pirkey-Ehrhart N, Withrow SJ, Straw RC, Ehrhart EJ, Page RL, Hottinger HL, Hahn KA, Morrison WB, Albrecht MR, Hedlund CS, et al.

  • Brodey RS, Misdorp W. Riser WH et al: Canine skeletal chondrosarcoma: A clinicopathologic study of 35 cases J Am Vet Med Assoc. 1974
  • J Am Vet Med Assoc. 1988 Jul 15;193(2):205-10.Jamshidi needle biopsy for diagnosis of bone lesions in small animals. Powers BE1, LaRue SM, Withrow SJ, Straw RC, Richter SL

  • Malignant Bone Tumors in the Dog, University of Pennsylvania School of Veterinary Medicine'

  • Clinical Veterinary Oncology, Stephen Withrow, E. Gregory MacEwan, J.B Lippincott Company 1989

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