Canine Osteochondrosarcoma

One Cancer With Many Names & Symptoms

Osteochondrosarcoma is a blanket term that covers several different types of bone neoplasms (abnormal growth in cells) and can also be referred to as chondroma rodens, multilobular osteoma, multilobular osteochondrosarcoma (MLO), calcifying aponeurotic fibroma (CAF) and juvenile aponeurotic fibroma (JAF) depending on the location and severity of the tumor. Characteristics these tumors share include: slow growth, high rates of recurrence after treatment and occurring more frequently in flat bones – most notably in the skull but can be spread to other bones in the spine, pelvis and palate.

What breeds or types of dogs are more likely to get multilobular osteochondrosarcomas?

While MLO tumors are often malignant, they are relatively uncommon in canines, however, there are some characteristics that may make your dog more susceptible to developing them. Medium or large breeds of dogs who are middle-aged or elderly are more likely to be affected by MLOs while it’s significantly less common very large breeds or smaller breeds.

What are the differences in the types of canine MLO tumors?

Canine Osteochondrosarcoma MLO tumors can be defined as a wide range of tumors throughout the dog’s body, however, most often this term refers to cancerous growths on the dog’s skull. The severity and treatment of these tumors can also vary to a large degree so it’s important to understand the different types of these tumors and what it means for your dog’s long-term health.

Multilobular osteochondrosarcoma (MLO) – also known simply as multilobular osteomas, it’s the general term for bone neoplasms originating in the skull or close-by flat bone structures.
Chondroma rodens – neoplasm growths in the internal occipital protuberance, cerebellar meninges and the cerebellum of a dog.
Calcifying aponeurotic fibroma (CAF) – a benign tumor that typically develops in the fascia and tendons of dogs. The condition is characterized by fibroblast proliferation with an indistinct border and calcification.
Juvenile aponeurotic fibroma (JAF) – a rare, benign tumor that develops in the appendages or extremities of younger dogs, and often manifests as a painless mass in the paws or tails of dogs.

What are the symptoms of MLOs and related tumors?

The vast majority of MLOs are not painful for dogs in and of themselves but after sustained growth can present related health issues known as secondary effects of the initial tumor or tumors. These secondary issues depend on the location of the MLO and how aggressively it spreads to other parts of the body. Typically, dog owners would see the following symptoms in their dogs:

Well-defined boney mass on the skull
A concentration of smaller boney masses in the skull
Secondary effects as the tumor spreads or grows larger

Sadly, these tumors can become painful to dogs if they spread close to nerves, vital organs or the spinal chord.

What are the diagnostics used to determine treatment?

MLO tumors are diagnosed using a combination of methods, usually starting with an examination by your veterinarian. The following methods may be used:

Medical evaluation – feeling and seeing abnormal growth on your dog’s skull is often the first step a veterinarian will take in assessing what is affecting your dog.
Radiographic methods – CT or MRI scans can show the bone neoplasms present on your dog.
Laboratory tests – blood work and serum biochemistry that assesses levels of alanine and aspartate aminotransferase, alkaline phosphatases, urea, creatinine, albumin and protein levels can indicate the presence of an MLO neoplasm.
Histologically – visual analysis of the surgically removed tumor (partial or full) under the microscope.

How is osteochondrosarcomas treated?

When your dog has a form of osteochondrasarcomas there are generally two accepted treatment methods, with varying degrees of severity. The cost of these treatments will also vary depending on your location and available treatments.

Surgical Resection of MLO tumors

Surgically removing the tumor is the most common treatment method of osteochondrasarcomas. This is suggested if the tumor has not spread and is in a place on the dog’s head that won’t cause further health complications if operated upon.

The downside of this treatment is that it is very difficult to remove the MLO tumor in its entirety. So while the vast majority of the tumor is removed, some remnants of the tumor can remain, making it more likely for the tumor to reform and create the same health issues as earlier. The upside of this procedure is that it can relieve the major symptoms your dog is experiencing and since the MLO tumors are typified for their slow growth, surgery won’t be immediately needed again.

Cranieoctomy surgery

Similar to trying to excise the tumor, cranieoctomies remove portions of the dog’s skull in hopes of removing the entire tumor to prevent possible regrowth. Healing from this procedure can be more intensive than excising just the tumor but it’s seen as a more complete way to treat MLOs.

Osteochondrosarcoma stereotactic radiotherapy

This is a form of external radiation therapy meant to shrink the bone neoplasms on a dog’s skull after several rounds of treatment. Unfortunately, stereotactic radiotherapy treatment is still seen as experimental and has varying effects on dogs suffering from tumors. This procedure is used more for the long-term management of MLOs and not wholly curative.

What is the prognosis for dogs with MLO?

It’s difficult to give a definitive prognosis for dogs suffering from MLO because it depends on the grade of the tumor, how it has or hasn’t spread throughout the body and the treatment methods that are appropriate for treating the tumor.

About half of dogs treated for osteochrondrosarcomas will see a return of the tumors and a little over half of the dogs will see the tumor metastasize. However, because the tumors are slow to grow treatments can still extend a dog’s life between 1.5 – 3 years in many cases.