The Dog Cancer Survival Guide (99 page)

*multiple tumors do not worsen the prognosis

In general, the higher the stage, the worse the prognosis becomes. The biopsy results offer you a great deal more information to consider, including the type of tumor (adenocarcinoma, cystadenocarcinoma, etc.) and its grade (aggressive characteristics). Other prognostic factors include: whether there is invasion into the lymphatics or the vascular system, whether estrogen or progesterone receptors are involved, and whether tumors are invasive or ulcerated.

Dogs of advanced age tend to have a less favorable prognosis, as do dogs that are not spayed. Small breeds tend to have more benign tumors than malignancies and live longer than larger breeds.

Surgery is the treatment of choice to remove mammary tumors, with the exception of IMC (see below). It’s important to remember that benign and malignant tumors can both develop at the same time, so every tumor should be addressed.

The number, location and size of tumors will determine the extent of the surgery. For each one, the entire tumor and all affected tissues should be removed with a wide (two-centimeter) margin. All masses will be submitted for biopsy, so that the type of each tumor can be determined, and the margins can be confirmed as clean. Radical mastectomies are usually not necessary for spayed dogs – a lumpectomy or a simple mastectomy (which removes just the mammary gland involved in the tumor) can suffice, as long as the excision is complete. Remember, 100% of benign and 50% of malignant tumors are cured with surgery alone, so approximately 75% of dogs with mammary tumors are treated with simple surgeries and then, potentially, are cured.

If your dog is intact, however, you might consider a radical mastectomy, which removes the entire chain associated with the tumor. A 2008 study reported that almost 60% of intact dogs who had a regional mastectomy later developed a secondary mass on the same side, in the same chain. This study’s results directly contradict what veterinary oncologists are traditionally taught about mammary cancer, which is that they should just remove the tumor with an adequate surgery. Since 75% of those secondary masses were malignant, discussing radical mastectomy with your oncologist is a good idea. Further studies are needed to look at whether radical mastectomies actually improve survival times for intact dogs, but they should be considered, based on the results of this study.

Would so many dogs have developed a second tumor if they were also spayed at the time of the first surgery (see below)? Unfortunately, we can’t know without another study; if your dog is intact, I recommend discussing spaying and/or a radical mastectomy with your oncologist.

The lymph nodes should also be considered for removal. For example, if your dog has a tumor at the back end of the chain – down near the rear legs – the inguinal lymph node will also be removed, even if it looks normal. The axillary (armpit) node, on the other hand, need only be removed if metastasis is confirmed or suspected. If there is metastasis in any lymph node, or if it is suspected, removing it should be seriously contemplated.

If your dog has IMC, or inflammatory mammary carcinoma, surgery may not be helpful because the surgical incision often does not heal well, due to the inflammatory nature of the cancer. Blood clotting abnormalities and edema can also occur. Treatment for IMC is usually palliative, not curative. NSAIDs can be used, as well as palliative radiation and palliative chemotherapy protocols. Surgery can still be considered, as sometimes just removing the inflamed, ulcerated mass will make your dog feel better.

The role of chemotherapy in treating mammary cancer in general has not been fully established, and there are no standard recommendations from the literature to share with you. One study looked at a small group of dogs, who had surgery along with a course of 5-FU and cyclophosphamide. They experienced significantly improved survival times, when compared to the control group, which had surgery only. Doxorubicin is commonly used in dogs with a high risk of metastasis. If you are contemplating chemotherapy, I strongly recommend consulting with a boarded oncologist who understands mammary cancer, because each case is so distinct.

The conventional treatments, which Dr. Ettinger recommends for mammary tumors, should be considered part of step one of Full Spectrum cancer care (
Chapter 11
). Please review that chapter for more general information about surgery, radiation and chemotherapy and how to handle common side effects.

For more information on all other Full Spectrum steps, including nutraceuticals, immune boosters, dietary changes and brain chemistry modification strategies, review Full Spectrum cancer care, which begins on
page 103
.

You will also find information about specific chemotherapy agents in
Chapter 41
.

In my experience, chemotherapy, for dogs with advanced stages of mammary tumors with a high risk for metastasis, can help maintain a good quality of life and delay or even prevent metastasis. I typically recommend post-operative chemotherapy, based on several prognostic factors, including: tumor size, stage, ulceration and full histopathology (which includes the tumor type, malignancy, vascular and/or lymphatic invasion, invasive nature and margins). Chemotherapy is best used when the disease is still in a microscopic form, because once metastasis has developed, chemotherapy is typically less effective. A careful consideration of your dog’s complete pathology is necessary to determine whether chemotherapy can be helpful or not – so make it a point to discuss this with your oncologist.

Radiation therapy is not widely used in dogs with mammary cancer, but it may be useful when a surgery results in incomplete margins and a second surgery is not possible. Also, radiation could be helpful when the mammary tumors are sarcomas, which are more likely to recur after surgery than other tumor types. Inoperable tumors may also benefit from a course of palliative radiation.

In addition to surgery and possibly chemotherapy or radiation, consider spaying your dog, if she is intact at the time of diagnosis. I mention this again because this topic is controversial among vets, however, two recent studies have shown that spaying at the time of surgery may increase survival times. Spaying may be particularly helpful for tumors with estrogen hormone receptors, because the spay removes the ovaries, and therefore the main source of estrogen. It’s possible that the variable outcomes in studies can be explained by this phenomenon: spaying helps if the tumors are estrogen responsive and doesn’t if they are not. Checking the status of estrogen receptors on your dog’s tumor would help you make this decision; unfortunately, this test is not commercially available. In general, I recommend spaying at the time of surgery or, when that is declined, a radical mastectomy, for intact dogs.

Hormonal therapy is the use of a drug to help block estrogen’s stimulation of the mammary tissue. Anti-estrogen therapies like tamoxifen, which are often used in human women, may not help your dog because, while your dog may have an estrogen-receptor positive tumor, these tumors tend to be benign and less-aggressive in dogs, and are often well-controlled by adequate surgery. More aggressive tumors in dogs do not usually have estrogen receptors and are less hormone-dependent. The side effects of anti-estrogen therapy can include: vulvar swelling, vaginal discharge, stump pyometra (a severe, possibly life-threatening infection of the “stump” of the uterus left after spaying), signs of heat and urinary tract infections. Because of these potentially severe side effects and the lack of evidence for efficacy, I do not generally recommend anti-estrogen therapy as a treatment.

All malignant mammary tumors have the potential for developing metastasis. For this reason, every dog with a confirmed malignancy should be rechecked periodically for new mammary tumors, even after a complete excision of the original tumor. Also, every dog should be staged periodically, for spread.

From my perspective as a veterinarian oncologist, mammary tumors are highly treatable with surgery. With 50% completely benign and only half of the malignancies prone to metastasize, your dog can really benefit from conventional treatments.

Early detection is critical. Stay vigilant about checking your dog for new masses, as the benefit of treating dogs with mammary tumors easily outweighs the risk of side effects. Treated dogs live significantly longer, are happy, run, play, sleep and eat, much as they did before they got sick.

O
steosarcoma accounts for the majority of bone cancers (85%) in dogs. Although it can develop in any bone in the body, three-quarters of these tumors develop in the limbs, with the front legs twice as likely to develop osteosarcoma as the hind legs.

Osteosarcoma (OSA) tumors grow fast and metastasize quickly. Ten to fifteen percent of dogs with osteosarcoma (OSA) already have detectable lung metastasis when they are first diagnosed and 90% have micrometastasis (spread that is not detected on chest X-rays). This incredibly high rate of micro-metastasis makes systemic chemotherapy treatments just as important as tumor removal. Despite its aggressive behavior, OSA is considered a highly treatable tumor.

The standard of care treatment for OSA is surgery, performed quickly, on the affected area, and then, chemotherapy to control the likely metastasis. Because so many OSA tumors are located in the limbs, the surgery is nearly always an amputation. Palliative radiation treatments can help to control pain, if surgery is not an option. Newer, alternative options for local control include limb-spare procedures and stereotactic radiosurgery, such as the CyberKnife.

OSA cases treated with amputation alone have a median survival time of four to five months, with 90-100% dying in one year and only 2% still alive after two years.

Median survival times for OSA cases treated with amputation and chemotherapy increase to ten to twelve months, with 20-25% of dogs still alive after two years. Several factors useful to help you determine your own dog’s prognosis will be reviewed in this chapter.