Uncommon Tumors: Primary Lung Tumors, Part 1

Why are primary lung tumors rare in dog cancer?

As a boarded oncologist, I see not only the common cancers in dogs like lymphoma, mast cell tumors, osteosarcomas, hemangiosarcomas, and mammary cancers. But I also see the uncommon ones.

Recently I have been seeing more of the uncommon tumors, and what’s even strange to me, I am seeing more that one within a few months of each other. For example, in the last few months, I have seen 2 dogs with insulinoma in the pancreas. Before these two, the last one I saw was probably over two years ago. This type of tumor secretes excessive amounts of insulin, the hormone your body normally secretes in response to eating a meal to lower your blood glucose (sugar). Since there is no control over the insulin production, insulin levels get too high, and blood glucose gets dangerously low. Insulinomas are infamous for being hard to find at abdominal surgery, so we often detect their presence because of their spread.

Also in the last two months, I have 2 patients with metastatic squamous cell carcinoma (SCC) in the tonsils. In both dogs with tonsillar SCC, a neck mass was found first, which was the metastatic lymph node – not the primary tumor in the back of the mouth – but the spread to the neck region.  Similar to insulinoma, the primary tumor can be small and the spread may be detected more easily. Check out my Facebook page to see one of the adorable dogs name Holly with tonsillar SCC that I am currently treating with metronomic chemotherapy (with Palladia).

In the Guide, I included 12 common canine tumors that I see and treat, but there was not enough space to go through some of the others. With my recent run of uncommon cases, I thought I would spend some time on some of the other less common tumors I see. Let’s start with lung tumors.

Primary lung cancer in dogs

When a client books an appointment with me, my staff asks what tumor they are seeing me for. My schedule often says something generic, usually: “a tumor in the lungs”.

There are two main types of lung tumors:

The first and most common type is another cancer that has spread to the lungs (for example, osteosarcoma).

The second type is primary lung cancer.

We will cover both in the upcoming posts, but let’s start with primary canine lung cancer.

Lung cancer is one of the top five human cancers and the leading cause of cancer related deaths worldwide and in the US.

In contrast, primary lung cancer is very rare in dogs and accounts for only 1% of all diagnosed cancers.  (As I stated above, metastatic cancer to the lungs – cancer that starts elsewhere and spreads to the lungs – is much more common in dogs.)

Primary canine lung cancer is typically seen in middle aged and older dogs (average age is 11 years). Some breeds that seem overrepresented include Boxers, Dobermans, Irish Setters, and Bernese Mountain Dogs.

Airborne carcinogens probably contribute, just like in people. One possible cause is environmental secondary smoke. There may also be an association with living in an urban environment. Interestingly, dogs with longer noses may get a protective benefit of the filtration in the nose and have less lung cancer than dogs with shorter noses, especially brachycephalic breeds (breeds with smushed noses like Pugs and English bulldogs).

The majority of primary lung tumors are malignant and carcinoma, most commonly adenocarcinoma, originating from the lung lining. Adenocarcinomas are classified based on location within the lung tissue (such as bronchial, bronchoalveolar, or alveolar).

Squamous cell carcinomas are less commonly reported in the lungs.

(Remember, the type of tumor is reported on the biopsy report – and we get that info most commonly once the tumor has been removed.)

Another important piece of information from the biopsy (also called the histology report) is the histological grade.

Grade is determined by the pathologist based on how aggressive the cells look under the microscope. Why is grade important?  Histological grade correlates with likelihood of metastasis (spread). For example, over 50% of undifferentiated adenocarcinomas and over 90% of squamous cell carcinomas will metastasize. Knowing this information helps me give my clients a prognosis after surgery, and helps them make their treatment decisions.

Dogs are often diagnosed with lung cancer as in incidental finding during a routine geriatric screen, which we will cover in the next blog. I will also go over symptoms, diagnostics, and treatment, and prognosis.

Live longer, live well,

Dr Sue