The Dog Cancer Survival Guide (98 page)

The other fifty percent of mammary tumors are malignant, and of those, fifty percent will metastasize. The most common malignant mammary tumors are: carcinomas, adenocarcinomas (malignant versions of adenomas) and cystadenocarcinomas (malignant versions of cystoadenomas).

Another malignant mammary tumor is the inflammatory mammary carcinoma (IMC). This aggressive tumor is noteworthy (even though it is less common than other malignancies) because of its high rate of growth and rapid metastasis.

All malignant tumors have the potential to spread, especially when left untreated. Breast cancer can metastasize to the lungs, regional lymph nodes, abdominal organs (such as the liver) and bones.

When you need to look up the definition of a word or phrase, find it listed in
Chapter 5
, which begins on
page 46
.

Mammary tumors are very rare in male dogs and very common in females. Also, they are quite prevalent in several specific breeds: Cocker Spaniel, Brittany Spaniel, English Springer Spaniel, Pointer breeds, Toy and Miniature Poodles, Dachshunds, Maltese, German Shepherds and Yorkshire Terriers. Both Boxers and Collies have a decreased risk for mammary tumors.

There are several other factors that may determine which dogs become afflicted. The biggest factor seems to be whether she has been spayed or not, and when. Females, spayed before their first heats, decrease their risk to only half a percent for developing mammary gland tumors. The risk increases to eight percent when the spay is performed between the first and second heats, and it jumps to 26% after the second heat cycle. In other words, females spayed after the second heat and intact females are seven times more likely to develop a mammary tumor than those spayed before six months of age!

The protective benefits of early spaying seem to derive from arresting the normal development of mammary glands, as the dog matures from puppy to adult. The early hysterectomy removes the ovaries, resulting in vastly reduced levels of the female sex hormones, estrogen and progesterone. Both of these have been associated with mammary tumor development; research has found both benign and malignant mammary tumors sometimes feature estrogen receptors, which seem to help transform normal mammary cells into cancerous cells (these receptors may be targets in future mammary cancer treatments).

The longer your dog’s body is exposed to the female sex hormones, the more likely she is to develop mammary cancer. Even dogs who were not spayed early can still get some benefit from a later surgery; spaying just before the age of two and a half years, while not completely preventative, affords some protection against developing mammary tumors later in life. Studies also show that when an intact female develops mammary tumors, spaying her will typically result in longer survival time.

Early obesity seems to play a role in mammary tumor development; dogs with lean bodies from age nine to twelve months are at decreased risk, while overweight dogs are at increased risk. In this same study, females fed a homemade diet were also at higher risk, and so were those that ate a lot of red meat, especially beef and pork, and little chicken.

Does this mean you are not to feed your dog the dog cancer diet Dr. Dressler recommends? I wouldn’t object to feeding the dog cancer diet, based only on this study. It’s important that you are aware of this link, and it’s important to know that diet plays a vital role in mammary cancer. However, diet is a very complex subject. If you feed the dog cancer diet, I certainly recommend you feed chicken (and other lean meats) and skip beef and pork for these dogs.

I would also modify your dog’s intake of dietary fat. Dietary fats are a significant contributing factor in mammary cancer. For example, low-fat, high-protein diets are associated with longer survival times than low-fat, low-protein diets. In the same study, survival times were not affected either way by a high-fat diet, regardless of protein intake. High levels of dietary fat tend to increase blood estrogen levels in women, leading to higher risk for breast cancer; the same thing may occur in female dogs.

Genetic mutations seem to be involved in the development of mammary cancers. Although the specific mutation has not yet been identified, candidates include: p53, c-erb-2 (HER-1/neu) and BCRA1 and BCRA2. In the future, as problematic mutations are identified, we may be able to target treatments to specific genes.

A direct association has recently been found between anaplastic (particularly aggressive) carcinomas and COX-2, an enzyme responsible for inflammation. The anaplastic tumors express a lot more COX-2 than adenocarcinomas, for example. If your dog has an anaplastic tumor, using a COX-2 inhibitor (like NSAIDs) may help control the tumor.

In human women, pregnancy provides some protection from breast cancer; this is not true for dogs. Whether your dog has lactated or not also does not affect her risk of developing mammary cancer.

Most mammary tumors are found by owners or by vets, during a routine physical exam. The mammary glands line up along both sides of the chest and abdomen chains. Most dogs have ten glands in total, five on each chain. Each gland is referred to by number, one to five on each side, with number one toward the head and number five toward the tail.

Tumors usually feel like small, discrete, firm balls right at the nipple; in the softer breast tissue, they feel more like diffuse masses. Most dogs do not seem sick when the tumor is found, and blood tests are usually normal.

More than one tumor is found in 60% of cases, although multiple tumors do not exacerbate her prognosis. Because the tumors can develop from more than one kind of mammary tissue, it’s important to examine each one to find out what cancer is present. The most common glands for cancer development are the fourth and fifth of either chain (located towards her tail end).

While benign tumors often feel like they are superficial and unattached to any other tissue, malignancies often seem attached or rooted to underlying tissues. Other hallmarks of malignancies include: ill-defined borders, ulceration (open sore), pain and swelling. Malignancies may also increase rapidly in size.

Although these characteristics have often been found in malignant tumors, their presence does not definitely indicate that the tumor is malignant. Conversely, their absence does not mean the tumor is benign. Every tumor should be biopsied, submitted to a lab, and examined for malignancy under a microscope.

Regional lymph nodes should also be examined. They can become enlarged due to normal inflammation, to metastasis or to a secondary infection from an ulcerated tumor. The most commonly affected nodes are the inguinal (inner thigh) and axillary (armpit). As the mammary tissue includes a complex lymph drainage system, the prescapular nodes in front of the shoulder, the popliteal nodes behind the knee, the sternal nodes in the chest cavity and the abdominal lymph nodes should all be examined, as well.

If breast cancer has spread by the time of diagnosis, your dog can show general signs of weakness, lethargy, and weight loss. The uncommon, aggressive inflammatory mammary carcinoma (IMC) can cause these same symptoms, plus others. As the name suggests, these tumors contain many inflammatory cells, and are associated with swelling, pain and rapid metastasis. They often involve the skin, which can become swollen, warm and red. IMC is frequently confused with mastitis (an inflammation of the breast tissue) because the breast becomes painful to the touch and can even ulcerate.

Once a tumor or tumors are found, each is measured and possibly aspirated, with a fine needle aspirate, to find out whether the mass is a mammary tumor, an infection or an inflammation. When the presence of a mammary tumor is confirmed, the aspirate can almost never show whether it is benign or malignant. To get that information, a biopsy must be performed.

The biopsy surgery will remove the entire mass, which is then examined under a microscope to check the margins and see whether it is benign or malignant. If the tumor is benign and margins are clean, this biopsy becomes the curative surgery.

If the tumor is malignant, further staging should be done to determine whether there is metastasis. When a tumor has the hallmarks of malignancy (it is very large, inflamed, stuck to underlying tissues, or regional lymph nodes are enlarged), your vet or oncologist may want to stage it, even before removing it with a biopsy.

To stage the malignancy, your vet may order a complete blood count (CBC), a chemistry panel, urinalysis, chest imaging (to check for spread to the lungs), an abdominal ultrasound (to check for spread to the abdominal organs) and aspirates of the draining lymph nodes, deep in the abdomen.

Enlarged lymph nodes can occur because of factors other than metastasis, so their size is not a good predictor of outcome. However, all regional lymph nodes should be checked for metastasis when malignant breast tumors are present.

The outcome for mammary tumors is extremely variable, because some are benign, others are malignant and each tumor type is so distinctive. With treatment, the overall median survival time is about fifteen months for all tumors (benign and malignant), and survival times of two years occur for 25-40% of all dogs with mammary tumors.

Dogs with benign tumors have significantly longer survival times than those with malignant tumors. The median survival time for dogs with benign tumors, removed with surgery, is approximately twenty-six months or over two years. (The reason there are median survival times associated with benign tumors is that even these tumors can recur if they are not completely removed.)

Dogs with malignant tumors have a more varied outcome. Low-grade malignant tumors, which are removed with clean margins, may be cured altogether – as if the tumor were benign – while others may recur and spread within the first year. Higher-grade tumors may recur and metastasize even sooner. In general, dogs whose malignancies are removed with surgery experience a sixteen-month median survival time.

Because of the many variables at play, each dog and each case must be considered carefully; however, we do have a few prognostic factors to review.

The stage – location where mammary tumors appear in the body – can be helpful in forecasting your dog’s outcome. Here is a modified version of the World Health Organization’s (WHO’s) Clinical Staging System for Mammary Gland Tumors:

Stage I:
Tumor(s)* are under three centimeter in diameter, with no regional lymph node involvement and no metastasis.

Stage II:
Tumor(s) are three to five centimeter in diameter, with no regional lymph node involvement and no metastasis.

Stage III:
Tumor(s) are over five centimeter in diameter, with no regional lymph node involvement and no metastasis.

Stage IV:
Tumor(s) are any size, with regional lymph node involvement.

Stage V:
Tumor(s) are any size, with regional lymph node involvement and metastasis.