Lung Metastases

 

Pulmonary metastases (lung met) is the most common location for osteosarcoma. Lung mets for the most part are asymptomatic and radiographs (3 views) is the only way to initially detect the nodules. A dog has 6 lung lobes; 4 on the right side and 2 on the left side. A dog can survive with 45% of the lung capacity gone.

Pulmonary Metastasectomy

    Removal of the lung met may be an option. To be a candidate for pulmonary metastesectomy, the following conditions are usually required:

  • Primary tumor in complete remission, preferably for a long relapse-free interval (>300 days).
  • 1 or 2 nodules visible on plain thoracic radiographs
  • Cancer only found in the lung (negative bone scan)
  • Long doubling time (>30 days) with no new visible lesions within this time
Nonspecific Immunomodulation Liposomal IL-2 in a small sample study showed promise. Unfortunately, this drug is not readily available. Free IL-2 is available, but the success rate has not been well documented.

Lipsome-encapsulated muramyl tripeptide phosphatidylethanolamine (L/MTP-PE)

Chemotherapy

In one study, the chemo agents of cisplatin, doxorubicin, or mitoxantrone failed to stop the progression of lung mets.

However, inhaled therapies are showing promise. Inhaled gemcitabine is currently in trial at UC Davis. (Jan 07)

Oral Cyclophosphamide, part of the metronomic protocol, is showing anecdotal success with some dogs.

Metronomic Protocol

The metronomic protocol is a protocol that can be introduced at any stage. It is often started at the presentation of lung mets.

Alternatives

Artemisinin is a Chinese Herb. Many are using Artemisinin, but no known study has been published.

Progression/Complications

Pulmonary metastases (lung met) often shows no visible signs. As the nodules grow, most dogs will slow down and may start showing flu-like symptoms. Runny nose and eyes are possible. However, sometimes, symptoms may be visible as listed below.

Coughing

If lung mets are close to the main bronchial tubes, they can cause irritation which can cause a cough. Likewise if they are near nerves or the diaphragm they can cause irritation and a cough. There are other reasons for a cough-reflux of acid from the stomach can do it, like heartburn. Reverse sneeze can sound like a cough, and sometimes mild forms of laryngeal paralysis can cause a cough, usually after eating or drinking. Suppressing the cough may help with symptoms.

Plueral Effusion

Another sign of metastases in the lung is when fluid builds up around the lungs. The lungs are covered in two layers of a saran wrap-like lining (called "pleura"). One layers covers the lung itself, the other covers the inside of the rib cage. The two are virtually inseparable and contain only enough fluid to allow for them to move smoothly against each other. When the saran wrap lining gets infected, inflamed or involved with cancer cells, the saran wrap develops small holes through which fluid leaks-fluid then accumulates between the two layers. This is called "pleural effusion". When this happens, fluid accumulates against the lungs, not inside them, and compresses the lungs, making it harder for them to expand with air. If the effusion is caused by cancer, the fluid accumulates quickly and even if drained or treated with diuretics (which do work to some extent), it usually returns fairly rapidly. So, metastases to the pleura will cause a "malignant effusion". This is different from actually having metastases in the lung tissue, which as we know, can go for a long time without causing symptoms.

Hypertrophic Ostoearthropathy (HO) :

HO is defined as the bilateral, symmetrical soft tissue swelling of the lower legs. Metastatic pulmonary lesions is the most common cause of HO. The limbs may be warm to the touch and are often painful when pressed. The dog may be reluctant to move and may show signs of lameness. In one study, HO symptoms were eliminated when the lung mets were surgically removed.

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Bone Metastases

 

Bone metastases is the second most common location. Radiographs or a bone scan (nuclear scintigraphy) are the common methods to diagnosis suspected metastatic sites.

Amputation and limb-spare are often options that are reserved for the primary tumor and normally not an option for bone metastases.

All treatment options are considered palliative:

  • Palliative radiation
  • Bisphosphonates
  • Metronomic Protocol
  • Chemotherapy may not be that effective as a stand-alone, but it is unclear of the effectiveness when combined with some of the other protocols.
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Brain Metastases

 

The incidence of metastatic brain tumors is unknown but believed to be very rare. Brain tumors can be suspected if the dog starts experiencing seizures. Diagnostic tests are normally cost prohibitive with very limited value-added.

Protocols normally address the symptoms and are considered palliative. Corticosteroids (dexamethasone and prednisone) are used to help reduce elevated intracranial pressure. Anti-convulsants (Phenobarbital) is used to control the seizures.

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