Healthy Pets

Cancer

posted: 05/15/12
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Cancer can affect virtually any organ or body system. Some are slow growing and some progress very rapidly. There are effective treatments for many types of cancers, and research is regularly identifying new ones. Early diagnosis has a significant effect on the success of treatment.

Hemangiosarcoma is an aggressive cancer that arises from the blood vessels. The cancer can occur anywhere in the body, but there are several locations that are more common. Early and aggressive treatment can lengthen the dog's life but this cancer is often metastatic and complete remission is rare.

Which dogs are at risk for developing hemangiosarcomas?

Hemangiosarcomas can occur in any dog regardless of breed, age, or sex. Hemangiosarcomas are rare in the cat and human. There are several breeds of dogs that seem to be at a greater risk for hemangiosarcoma and they include German Shepherds, Golden Retrievers, Boxers, and English Setters.

We do not currently understand why dogs develop hemangiosarcomas. Because of the increased incidence in several breeds, a genetic link appears to be one of several likely causes. Hemangiosarcoma is rarely found in humans, so less research has been done, and the amount of information about the cause of this tumor is somewhat limited.

What are the symptoms of hemangiosarcoma?

Hemangiosarcomas can occur anywhere on or in the body but primarily are present in the spleen, liver, heart and skin. The skin form of hemangiosarcoma has a better prognosis and recovery rate than the internal forms. The skin form is occasionally present in cats and can sometimes be associated with sun damage on light-skinned/haired animals. The internal form is usually diagnosed by the palpation of a large mass in the abdomen or with symptoms of sudden blood loss. The sudden blood loss results from the rupture of the fragile tumor and a resulting loss of blood into the abdomen. The symptoms would include weakness or collapse and pale mucous membranes. Occasionally dogs will have symptoms of chronic blood loss which include pale gums, slow capillary refill time (CRT), irregular heart rate and generalized weakness.

How is hemangiosarcoma diagnosed?

Once a tumor is suspected, abdominal and chest x-rays are often performed to determine the extent of organ involvement and whether or not metastasis is present. Hemangiosarcoma is an aggressive tumor and metastases are often present at the time of initial diagnosis. A biopsy or positive identification of a removed tumor by a veterinary pathologist is usually recommended.

What is the treatment for hemangiosarcoma?

Hemangiosarcoma is primarily treated with a combination of surgery and chemotherapy. Surgical removal alone is often not very rewarding. Because of the high risk of metastasis, the average survival time without chemotherapy is one to two months, with less than 10 % of the dogs living a year. With surgical removal and accompanying chemotherapy, the average survival time increases to 5 to 7 months. However 90% of these dogs still don't survive more than a year after initial treatment. Success rates can improve depending on location and early intervention. Skin-based hemangiosarcomas appear less likely to be metastatic when initially diagnosed and treatment is more often successful. Surgical removal of the skin-based tumors can be curative, however chemotherapy is often recommended in addition to surgery. Because of the aggressive nature of hemangiosarcomas and the rapidly changing chemotherapy drugs, I recommend that all owners of dogs with hemangiosarcomas seek out treatment or advice from a veterinary oncologist.

Conclusion

In summary, hemangiosarcoma is a somewhat common tumor in dogs. It can be found in any dog but has some definite breed predilections. Most of the tumors are metastatic and aggressive and have a guarded outcome. With early detection and treatment with surgery and chemotherapy survival times and quality of life can be improved.

Histiocytomas can affect dogs of any age. They can appear on any location on the body, however, the vast majority of histiocytomas appear on the head. Histiocytomas usually occur on dogs under three years of age; histiocytomas are one of the most common tumors in this age group. The breed or sex of the dog does not appear to influence their development.

These tumors appear rapidly and are small, round, and hairless. They will often ulcerate and then become smaller and go away. They usually appear as a solitary mass, but more than one may be present at a time. These tumors are benign and are not considered to be a health risk.

Treatment often involves just letting the tumor run its course. Histiocytomas can be surgically removed if they are bothering the dog and are in a location where the removal will allow for closure of the skin. They can also be treated with topical steroids and antibiotics if they ulcerate, become inflamed or infected. However, most dogs never receive nor require any treatment intervention. If you see a small tumor that develops on your dog make sure to have it examined by your veterinarian.

Lymphosarcoma is a common cancer of lymphocytes in dogs and can occur in the lymph nodes, spleen, liver and other organs. The cancer can be aggressive and if left untreated can lead to a high mortality. Treatment with chemotherapy has been very successful adding months and occasionally years to the dog's life.

Which dogs are at risk for developing lymphomas?

Lymphomas primarily affect middle age to older dogs. There does not appear to be a breed or sex predilection. Only 10% to 20% of dogs are clinically ill at presentation, the majority are brought in because of recently identified swellings or lumps.

Why do dogs develop lymphoma?

While we understand how lymphomas form, we still do not understand why. In cats there appears to be a strong link between some forms of lymphoma and infection with feline leukemia virus, however in dogs such a link is not apparent. Some authors have speculated that environmental factors such as exposure to pesticides or strong magnetic fields increase the incidence, but there is currently no strong proof of this. At the same time, some authors have also hinted at a possible genetic correlation, but further studies need to be performed to determine the exact risk factors involved in canine lymphoma.

What are the symptoms of lymphoma?

The symptoms of lymphoma are related to the location of the tumor(s). Tumors that develop in the lymph nodes often present as swellings with no other symptoms. The gastrointestinal form often is accompanied with vomiting, diarrhea, weight loss and lack of appetite. The mediastinal (chest) form often presents with shortness of breath and muffled heart sounds. The cutaneous (skin) form can present in several different ways including single or multiple lumps in the skin, or mouth. These bumps can itch or be red and ulcerated.

How is lymphoma diagnosed?

Lymphoma is diagnosed with a combination of diagnostic tests. Blood tests, fine needle aspirates of the tumor, biopsies, x-rays and ultrasound are all used to confirm the diagnosis of lymphoma. The exact tests performed will depend on the location of the tumor.

Testicular tumors are considered one of the most common tumors in older intact (unneutered) male dogs. The overall incidence in dogs is not very high because of the large number of dogs that are castrated. However, in intact male dogs these tumors are considered fairly common. The tumors are usually fairly easy to recognize and diagnose. Treatment consists of castration and is usually curative.

Which dogs are at risk to develop testicular tumors?

Testicular tumors are most common in intact (unneutered) older male dogs. However, they can occur in intact males of any age. There does not appear to be any breed predilection for this tumor. The current cause of testicular tumors is unknown. Dogs that have one or both testicles that are not descended (cryptorchid) are 13 times more likely to develop a tumor in the undescended testicle than dogs with normal testicles. Except for the increased risk of these tumors in cryptorchid dogs, no other risk factors are readily apparent.

Are there different types of testicular tumors?

There are three common types of testicular tumors: Sertoli cell tumors, seminomas, and interstitial cell tumors. While there are differences in the types of tumors, they are often treated similarly and are therefore commonly lumped together as testicular tumors.

What are the symptoms?

Sertoli cell tumors show symptoms of swelling of the testicular and scrotal area. If the dog is cryptorchid the swelling will occur in the inguinal or abdominal area depending on the location of the testicle. Up to 50% of the Sertoli cell tumors will produce estrogen and the dog will suffer symptoms of hyperestrogenism. These include an enlarged prostate gland, enlarged mammary glands and nipples, symmetrical hair loss, anemia, and the tendency to attract other male dogs. Sertoli cell tumors may metastasize to the abdomen, lung, thymus and brain, however this occurs in less than 15% of the cases.

Seminomas will also appear as swellings of the testicle, scrotum and inguinal or abdominal area. Seminomas produce estrogen or metastasize in less than 5% of the reported cases.

Interstitial cell tumors show very few symptoms and do not produce estrogen or metastasize. They are usually incidental findings and not considered to be much of a problem.

How are testicular tumors diagnosed?

Diagnosis is based on history, presentation, and pathological identification through a biopsy or microscopic examination of the removed tumor. Dogs suspected of a testicular tumor should also have abdominal and chest x-rays to check for metastasis as well as a chemistry panel and a blood count (CBC).

What is the treatment for testicular tumors?

Treatment usually consists of surgical castration. Because of the success of testicular removal and the low rate of metastasis, castration is often the only treatment needed. Some dogs have been treated successfully with chemotherapy and in dogs that have metastasis, chemotherapy is sometimes recommended.

What is the prognosis for dogs that develop testicular tumors?

The prognosis for dogs with treated testicular cancer is usually very good. The low rate of metastasis makes surgical castration very successful and curative in most dogs. Dogs that develop hyperestrogenism from Sertoli cell tumors will often have a regression of symptoms, once the tumor has been removed. In severe hyperestrogenism that results in anemia, some animals may require transfusions and more aggressive treatment. The prognosis for testicular tumors that have metastasized is more guarded and the outcome varies widely depending on location, type and treatment.

How can testicular tumors be prevented?

Testicular tumors are easily prevented through routine castration of male dogs. Castration in young dogs prevents aggression, roaming, urine marking and a variety of other unwanted male behaviors. The surgery is safe and relatively inexpensive and in the long run saves the owner money. Dogs that are used for breeding can be castrated when they are no longer used for breeding. Dogs that are cryptorchid should always be castrated and the owner should insist that both testicles be removed. Since cryptorchidism is considered to be an inherited trait, cryptorchid dogs should never be used for breeding. Because the retained testicle is 13 times more likely to develop a tumor, it should always be removed.

Mammary tumors are the most common tumors in female dogs who have not been spayed. Mammary tumors can be small simple nodules or large aggressive metastatic growths. With early detection and prompt treatment, even some of the more serious tumors can be successfully treated. Cats also suffer from mammary tumors and they have there own unique set of problems that are discussed in the Cat Health Center.

Which dogs are at risk for developing mammary tumors?

Mammary tumors are more common in unspayed, middle-aged female dogs (those between 5 and 10 years of age), although they can, on rare occasions, be found in dogs as young as 2 years. These tumors are rare in dogs that were spayed under 2 years of age. Occasionally mammary tumors will develop in male dogs and these are usually very aggressive and have a poor prognosis.

Spaying greatly reduces the chances of a female dog developing this condition. In those females spayed prior to their first heat cycle, breast cancer is very, very rare. Those that are spayed after their first heat but before their fourth heat or before 2.5 years of age will have a somewhat decreased incidence of breast cancer than those who are never spayed. Those spayed after 2.5 years of age have the same incidence of disease as those who were never spayed. It is believed that the elimination or reduction of certain hormonal factors causes the lowering of incidence of the disease in dogs that have been spayed. These factors would probably be estrogen, progesterone, a similar hormone or possibly a combination of two or more of these.

What are the types of mammary tumors in dogs?

There are multiple types of mammary tumors in dogs. Approximately one-half of all mammary tumors in dogs are benign, and half are malignant. All mammary tumors should be identified through a biopsy and histopathology (microscopic examination of the tissue) to help in the treatment of that particular type of tumor.

The most common benign form of canine mammary tumors is actually a mixture of several different types of cells. For a single tumor to possess more than one kind of cancerous cell is actually rare in many species. This combination cancer in the dog is called a 'benign mixed mammary tumor' and contains glandular and connective tissue. Other benign tumors include complex adenomas, fibroadenomas, duct papillomas, and simple adenomas.

The malignant mammary tumors include: tubular adenocarcinomas, papillary adenocarcinomas, papillary cystic adenocarcinomas, solid carcinomas, anaplastic carcinomas, osteosarcomas, fibrosarcomas and malignant mixed tumors.

What are the symptoms of mammary tumors?

Mammary tumors present as a solid mass or as multiple swellings. When tumors do arise in the mammary tissue, they are usually easy to detect by gently palpating the mammary glands. When tumors first appear they will feel like small pieces of pea gravel just under the skin. They are very hard and are difficult to move around under the skin. They can grow rapidly in a short period of time, doubling their size every month or so. The dog normally has five mammary glands, each with its own nipple, on both the right and left side of its lower abdomen. Although breast cancer can and does occur in all of the glands, it usually occurs most frequently in the 4th and 5th. In half of the cases, more than one growth is observed. Benign growths are often smooth, small and slow growing. Signs of malignant tumors include rapid growth, irregular shape, firm attachment to the skin or underlying tissue, bleeding, and ulceration. Occasionally tumors that have been small for a long period of time may suddenly grow quickly and aggressively but this is the exception not the rule. It is very difficult to determine the type of tumor based on physical inspection. A biopsy or tumor removal and analysis are almost always needed to determine if the tumor is benign or malignant, and to identify what type it is. Tumors which are more aggressive may metastasize and spread to the surrounding lymph nodes or to the lungs. A chest x-ray and physical inspection of the lymph nodes will often help in confirming this. Mammary cancer spreads to the rest of the body through the release of individual cancer cells from the various tumors into the lymphatics. The lymphatic system includes special vessels and lymph nodes. There are regional lymph nodes on both the right and left sides of the body under the front and rear legs. They are called the 'axillary' and 'inguinal' lymph nodes, respectively. Mammary glands 1, 2, and 3 drain and spread their tumor cells forward to axillary lymph nodes while cells from 3, 4, and 5 spread to the inguinal ones. New tumors form at these sites and then release more cells that go to other organs such as the lungs, liver, or kidneys.

What is the treatment?

Surgical Removal: Upon finding any mass within the breast of a dog, surgical removal is recommended unless the patient is very old. If a surgery is done early in the course of this disease, the cancer can be totally eliminated in over 50% of the cases having a malignant form of cancer. The area excised depends on the judgment and preference of the practitioner. Some will only remove the mass itself. Others, taking into consideration how the cancer spreads, will remove the mass and the rest of the mammary tissue and lymph nodes that drain with the gland. For example, if a growth were detected in the number 2 gland on the left side, we would therefore remove glands, 1, 2, and 3 and the axillary lymph node on that side. If it were found in the number 4 gland on the right side, then glands 3, 4, 5 and the inguinal lymph node on that side would be completely removed. With some tumor types, especially sarcomas, complete removal is very difficult and many of these cases will have tumor regrowth at the site of the previously removed tumor. Owners may confuse a surgical removal of a mammary gland in the dog with a radical mastectomy in humans, with all of the associated problems. In humans, this type of surgery would affect the underlying muscle tissue which complicates the recovery. In the dog, however, all of the breast tissue and the related lymphatics are outside of the muscle layer so we only need to cut through the skin and the mammary tissue. This makes the surgery much easier and recovery much faster. A radical mastectomy in a dog means all the breasts, the skin covering them, and the four lymph nodes are all removed at the same time. Although this is truly major surgery, suture removal usually occurs in 10 to 14 days with normal activity resuming at that point. Many veterinarians will spay a dog having a mastectomy (unless she is very old). The value of this in decreasing the recurrence of tumors is still controversial. Chemotherapy and Radiation Therapy: Chemotherapy has not been a very successful nor widely used treatment for mammary tumors in dogs. However, with the constantly changing and improving drugs available, a veterinary oncologist should be consulted to find out if there is an effective drug available for your dog's particular type of mammary cancer. The effectiveness of radiation therapy has not been thoroughly researched. Some anti-hormonal drug regimens are being tested in dogs. At this point in time, surgical removal of the tumors is the treatment of choice.

How can I prevent mammary cancer in my dog?

There are few cancers that are as easily prevented as mammary cancer in dogs. There is a direct and well-documented link between the early spaying of female dogs and the reduction in the incidence in mammary cancer. Dogs spayed before coming into their first heat have an extremely small chance of ever developing mammary cancer. Dogs spayed after their first heat but before 2.5 years are at more risk, but less risk than that of dogs who were never spayed, or spayed later in life. We all know the huge benefits of spaying females at an early age but, every day, veterinarians still deal with this easily preventable disease. Early spaying is still one of the best things pet owners can do to improve the health and insure a long life for their dogs.

Conclusion

Mammary cancer is a very common cancer and can often be successfully treated if caught early. If all non-breeding dogs and cats were spayed before their first heat this disease could be almost completely eliminated. If you find a growth or lump in the mammary tissue of your dog, you should inform your veterinarian immediately and not take a "wait and see" attitude.

Canine mast cell tumors account for up to 20% of all skin tumors in dogs. While they often appear small and somewhat insignificant, they can be a very serious form of cancer in the dog. Some mast cell tumors are easily removed without the development of any further problems and others can lead to a life threatening disease. Proper identification and treatment are very important in controlling this disease.

Which dogs are at risk for developing mast cell tumors?

Mast cell tumors can develop in all ages and breeds of dogs. They are very rare in cats and humans. There appears to be a hereditary factor to these tumors as shown by some strong breed predilections. Dachshunds, English Bulldogs, Fox Terriers, and Staffordshire Terriers are all at increased risk. Boxers and Boston Terriers are at even higher risk and appear to have certain genes that make them more susceptible to the disease. One study has indicated that younger dogs that develop mast cell tumors are not as likely to develop the more severe forms of the cancer.

The exact cause of mast cell tumors is still speculative. A viral source has been mentioned, as well as hereditary and environmental factors. It is quite possible that there are a variety of different causes for the development of this tumor. Because this tumor is not found in humans, there has not been as much research and information available for the veterinarian as there are for tumors that are found in both humans and animals.

What are the symptoms of mast cell tumors?

The appearance of mast cell tumors can be widely variable. They can be either benign or malignant and can be found on any part of the body. They are found most commonly on the trunk, limbs and perineal (genital) area. Tumors can be found on the skin or in the underlying or subcutaneous tissue. They can be single or multiple and can be smooth, bumpy or even ulcerated. As you can see, they come in a variety of shapes and locations so a good diagnostic workup is necessary to properly identify a growth as a mast cell tumor.

Because of the large amounts of histamine, heparin and proteolytic enzymes (enzymes which break down protein) present in mast cell tumors, they can create problems when damaged or removed. Sites where the tumors are removed can sometimes refuse to heal and can become difficult to manage. There can also be systemic signs, such as vomiting and duodenal ulcers, that result from the release of these substances from the active mast cell tumors.

How are mast cell tumors treated?

Mast cell tumors are usually treated by surgical removal. It is important that the tumor is carefully removed and a large area of 'healthy' tissue around the tumor is also removed. In some cases surgical removal may not be an option. With surgical removal it should be noted that in up to 50% of the cases the tumor might regrow. Radiation therapy after surgical removal appears to be beneficial and may reduce the incidence of reoccurrence and increase survival rates. When dealing with mast cell tumors and their wide variety of forms, it is important to remember that each animal needs to be evaluated and treated individually.

Conclusion

Mast cell tumors can present in a wide variety of ways and can have an equally varied set of symptoms and outcomes. Because it is difficult to diagnose a mast cell tumor by visual inspection, it is important that all suspicious looking skin tumors be examined by a veterinarian and followed up with diagnostic testing and identification. Treatment consists of surgical removal and radiation. As with all tumors, prompt recognition and treatment is very important in obtaining the best possible outcome.

Osteosarcomas account for only 5% of all canine tumors, but 80-90% of malignancies involving the bone. Much more common in large breed dogs, osteosarcoma is an aggressive cancer of the bone that often requires amputation of the affected limb coupled with chemotherapy to provide temporary relief from this aggressive disease.

Which dogs are at risk for developing osteosarcomas?

Osteosarcomas generally affect older large or giant breed dogs. The giant breeds at greatest risk for developing osteosarcoma include Great Danes, St. Bernards, Great Pyrenees, Newfoundlands, Bernese Mountain Dogs, and Irish Wolfhounds. Large breeds such as Rottweillers, Labradors, Golden Retrievers, Shepherds, Dobermans, Weimaraners and Boxers are also at an increased risk. It is not a very common tumor in small breed dogs and rarely occurs in cats. Dogs that weigh over 80 pounds have been shown to be at least 60 times more likely to develop an osteosarcoma than dogs weighing less than 75 pounds. While older dogs more commonly develop osteosarcomas, there does appear to be an increased incidence in one to two year old dogs as well. Male dogs have an increased incidence of osteosarcomas.

It is unknown why some dogs develop osteosarcomas, but one theory suggests that the rapidly growing cells found at the growth plates in the bones are genetically at a greater risk of mutation. Another theory is that the tumors develop at the site of trauma. The increased cellular activity at the site of a fracture or trauma could result in the development of cancer cells. The reality is that both of these may be true and there may be other causes not yet discovered.

What are the symptoms of osteosarcomas?

The symptoms of osteosarcomas are often closely associated with their location. Most osteosarcomas develop on the limbs of dogs below the elbow or near the knee. The tumors usually form at or near the growth plates. Affected dogs will often have a pronounced bone swelling. X-rays often reveal a characteristic bone pattern that, coupled with history and breed, may indicate the development of an osteosarcoma. These tumors often produce pain in the joint that can first be detected as lameness in the affected limb. Up to 90% of these tumors will have metastasis to the lungs at the time of diagnosis but because of the small initial size of the metastases, less than 10% will initially show up on a chest x-ray. Because of this high incidence of metastasis, all dogs with osteosarcomas are treated as if they have metastasis to the lungs regardless of the findings on the initial lung x-rays. Osteosarcomas will occasionally show up at different locations and likewise other tumor types can initially appear to be an osteosarcoma. Because of this possibility, a biopsy is always recommended. Fungal bone infections can produce similar symptoms and appearance on an x-ray, so a fungal culture is often performed to help clarify the diagnosis.

What is the treatment for osteosarcoma?

Osteosarcoma is an aggressive, highly metastatic cancer that requires an aggressive treatment protocol. Once the tumor has been positively identified as an osteosarcoma, the affected limb is usually amputated. In rare cases where the tumor is in the right location, some limb sparing surgeries have been performed but that is not usually the case. After the amputation, a course of chemotherapy is usually begun. The most successful drugs have been carboplatin and cisplatin. Carboplatin is more expensive but safer and easier to administer. Doxorubicin is sometimes used as well. A qualified veterinary oncologist is often the best source of information and he or she will be aware of the newest chemotherapy protocols. The life expectancy of a dog with a properly identified and treated osteosarcoma varies greatly, but can approach a year or longer.

Is osteosarcoma preventable?

It does not appear that osteosarcoma is preventable. Because of some strong breed correlations, any breed line that has a history of osteosarcoma should be examined closely prior to breeding. Unfortunately we do not completely understand the cause of osteosarcoma but, hopefully as our knowledge improves, we can continue to provide more effective treatments and early diagnostic tests.

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