Cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
is the leading cause of death in
dogs
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
.
It is estimated that 1 in 3 domestic dogs will develop cancer, which is the same incidence of cancer among humans.
Dogs can develop a variety of cancers and most are very similar to those found in humans. Dogs can develop
carcinoma
Carcinoma is a malignancy that develops from epithelial cells. Specifically, a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that arises from cells originating in the endodermal, mesodermal ...
s of epithelial cells and organs,
sarcomas
A sarcoma is a malignant tumor, a type of cancer that arises from transformed cells of mesenchymal (connective tissue) origin. Connective tissue is a broad term that includes bone, cartilage, fat, vascular, or hematopoietic tissues, and sarco ...
of connective tissues and bones, and
lymphoma
Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). In current usage the name usually refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include enlar ...
s or
leukemia
Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ' ...
s of the circulatory system. Selective breeding of dogs has led certain pure-bred breeds to be at high-risk for specific kinds of cancer.
Veterinary oncology is the medical study of cancer in animals, and can be diagnosed and treated by specialized veterinarians called veterinary oncologists.
Causes
Cancer is a complex, multifactorial disease.
Carcinogenesis is linked with DNA mutations, chromosomal translocations, dysfunctional proteins, and aberrant cell cycle regulators.
Cancer alters the DNA of cells and the mutated genetic material is passed on to daughter cells, resulting in
neoplasm
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
s.
The mutated DNA effects genes involved with the
cell cycle
The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and subs ...
, classified as either
oncogene
An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels. s or
tumor suppressor gene
A tumor suppressor gene (TSG), or anti-oncogene, is a gene that regulates a cell during cell division and replication. If the cell grows uncontrollably, it will result in cancer. When a tumor suppressor gene is mutated, it results in a loss or red ...
s.
Oncogenes are responsible for cell proliferation and differentiation.
Oncogenes responsible for cell growth are overexpressed in cancerous cells. Tumor suppressor genes prevent cells with erroneous cell cycles from replicating.
Cancer cells ignore cell cycle regulators that control cell growth, division, and death.
The histology of spontaneous tumorigenesis in canines is attributed to the multiplicity and complexity of the disease. The heterogeneity of its development encompasses inherited, epigenetic, and environmental factors.
The
selective breeding
Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant mal ...
techniques used with domestic dogs causes certain breeds to be at high risk for specific cancers. Selection for specific phenotypes in dog breeding causes long-range
linkage disequilibrium
In population genetics, linkage disequilibrium (LD) is the non-random association of alleles at different loci in a given population. Loci are said to be in linkage disequilibrium when the frequency of association of their different alleles is h ...
in their DNA.
Certain areas of alleles have the tendency to separate less frequently than normal random segregation, which leads to long ranges of repeated DNA sequences. These repeated sequences caused by decreased genetic diversity within breeds, can lead to a high prevalence of certain diseases and especially cancer in breeds. It is believed that the breeding and inbreeding of domesticated canines for specific traits has significantly decreased nucleotide diversity in many pedigree dogs, making certain varieties of canines more susceptible to developing cancer.
Symptoms
Symptoms of cancer in dogs may include:
*Lumps (which are not always malignant, but should always be examined by a vet)
*Swelling
*Persistent sores
*Abnormal discharge from any part of the body
*Bad breath
*Listlessness/lethargy
*Rapid, often unexplained weight loss
*Sudden lameness
*Offensive odor
*Black, tarry stools (a symptom of ulcers, which can be caused by mast cell tumors)
*Decreased or loss of appetite
*Difficulty breathing, urinating or defecating
Types of cancer
Dogs can develop many of the same types of cancer as humans. Many canine cancers are described with the same terminology and use the same classification systems as human cancers.
* Mast cell tumors are the most common type of
skin cancer in canines.
* Lymphoma
* Prostate cancer
* Brain cancer
Hemangiosarcoma
Hemangiosarcoma is a rapidly growing, highly invasive variety of cancer that occurs almost exclusively in dogs, and only rarely in cats, horses, mice, or humans (vinyl chloride toxicity). It is a sarcoma arising from the lining of blood vessels; ...
is a type of cancer that develops almost exclusively in dogs, the only two other species known to have it are cats and horses. Hemangiosarcomas are tumors that form on the blood vessels, and can occur all over the body. These tumors can develop on the skin, subcutaneously, or on a blood vessel within an organ and are highly malignant. The tumors are most fatal when they rupture, causing the dog to suffer from severe loss of blood, or
hypovolemia.
Dogs are one of three mammalian species that are known to suffer from a transmissible cancer.
Canine transmissible venereal tumor (CTVT) is species specific and highly contagious.
The cancerous cell lines are transmitted between individuals that are in close contact with each other through acts of intercourse, biting, scratching, or licking.
The cancer is prevalent in populations of stray dogs or environments of uncontrolled copulation.
The tumors occur around the area of external genitalia and can grow up to 15 cm in area.
Canine transmissible venereal tumors can often be infected, ulcerated, and hemorrhagic.
Susceptibility
Cancer prevalence in dogs increases with age and certain breeds are more susceptible to specific kinds of cancers. Millions of dogs develop spontaneous tumors each year.
Boxers,
Boston Terriers and
Golden Retriever
The Golden Retriever is a Scottish breed of retriever dog of medium size. It is characterised by a gentle and affectionate nature and a striking golden coat. It is commonly kept as a pet and is among the most frequently registered breeds ...
s are among the breeds that most commonly develop
mast cell tumor
A mastocytoma or mast cell tumor is a type of round-cell tumor consisting of mast cells. It is found in humans and many animal species; it also can refer to an accumulation or nodule of mast cells that resembles a tumor.
Mast cells originate f ...
s. Large and giant breeds, like
Great Dane
The Great Dane is a large sized dog breed originating from Germany. The Great Dane descends from hunting dogs from the Middle Ages used to hunt wild boar and deer, and as guardians of German nobility. It is one of the largest breeds in the worl ...
s,
Rottweiler
The Rottweiler (, ) is a breed of domestic dog, regarded as medium-to-large or large. The dogs were known in German as , meaning Rottweil butchers' dogs, because their main use was to herd livestock and pull carts laden with butchered mea ...
s,
Greyhound
The English Greyhound, or simply the Greyhound, is a breed of dog, a sighthound which has been bred for coursing, greyhound racing and hunting. Since the rise in large-scale adoption of retired racing Greyhounds, the breed has seen a resurge ...
and
Saint Bernards, are much more likely to develop
bone cancer
A bone tumor is an abnormal growth of tissue in bone, traditionally classified as noncancerous (benign) or cancerous (malignant). Cancerous bone tumors usually originate from a cancer in another part of the body such as from lung, breast, thyro ...
than smaller breeds.
Lymphoma occurs at increased rates in Bernese Mountain dogs, bulldogs, and boxers.
It is important for the owner to be familiar with the diseases to which their specific breed of dog might have a breed predisposition.
[
A study of 144 female dogs found that dogs eating higher amounts of ]red meat
In gastronomy, red meat is commonly red when raw and a dark color after it is cooked, in contrast to white meat, which is pale in color before and after cooking. In culinary terms, only flesh from mammals or fowl (not fish) is classified as ...
, especially beef
Beef is the culinary name for meat from cattle (''Bos taurus'').
In prehistoric times, humankind hunted aurochs and later domesticated them. Since that time, numerous breeds of cattle have been bred specifically for the quality or quantity ...
and pork
Pork is the culinary name for the meat of the domestic pig (''Sus domesticus''). It is the most commonly consumed meat worldwide, with evidence of pig husbandry dating back to 5000 BCE.
Pork is eaten both freshly cooked and preserved; ...
, were more likely to get mammary cancer
A mammary tumor is a neoplasm originating in the mammary gland. It is a common finding in older female dogs and cats that are not spayed, but they are found in other animals as well. The mammary glands in dogs and cats are associated with their ...
.
Treatment
Treatment options vary and depend on the type and stage of cancer. Common treatments include surgery
Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...
, chemotherapy
Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemotherap ...
, radiation therapy
Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radia ...
, amputation, and immunotherapy
Immunotherapy or biological therapy is the treatment of disease by activating or suppressing the immune system. Immunotherapies designed to elicit or amplify an immune response are classified as ''activation immunotherapies,'' while immunotherap ...
. A combination of therapies may be used. Knowledge and treatment of cancer have increased significantly in the past three decades. Survival rates have also increased due to the increased prevalence of canine cancer treatment centers and breakthroughs in targeted drug development. Canine cancer treatment has become an accepted clinical practice and access to treatment for owners has widely expanded recently. Cancer-targeting drugs most commonly function to inhibit excessive cell proliferation by attacking the replicating cells.
There is one canine tumor vaccine approved by the USDA
The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of com ...
, for preventing canine melanoma. The Oncept vaccine activates T-cell
A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...
responses and antibodies against tumor-specific tyrosinase
Tyrosinase is an oxidase that is the rate-limiting enzyme for controlling the production of melanin. The enzyme is mainly involved in two distinct reactions of melanin synthesis otherwise known as the Raper Mason pathway. Firstly, the hydroxy ...
proteins. There is limited information about canine tumor antigens, which is the reason for the lack of tumor-specific vaccines and immunotherapy treatment plans for dogs.
Success of treatment depends on the form and extent of the cancer and the aggressiveness of the therapy. Early detection offers the best chance for successful treatment. The heterogeneity of tumors makes drug development increasingly complex, especially as new causes are discovered. No cure for cancer in canines exist.
Some dog owners opt for no treatment of the cancer at all, in which case palliative care
Palliative care (derived from the Latin root , or 'to cloak') is an interdisciplinary medical caregiving approach aimed at optimizing quality of life and mitigating suffering among people with serious, complex, and often terminal illnesses. Wit ...
, including pain relief, may be offered. Regardless of how treatment proceeds following a diagnosis, the quality of life of the pet is an important consideration. In cases where the cancer is not curable, there are still many things which can be done to alleviate the dog's pain. Good nutrition and care from the dog's owner can greatly enhance quality of life.[
]
Prognosis
According to Blue Cross, pet owners can expect for their pet to live about 12 months with current treatments. If the owner opts for palliative care instead of treatment, the dog will live about 3 months, although if the tumor is partially removed this can be extended. The survival time may be longer in large dogs, and the cure rate is 20%. If a tumor is completely removed, usually the pet will receive small doses of radiation in hopes of preventing recurrence. The survival rates are: 1 year: 59%, 3 year: 40%, 5 year: 13%.
References
{{reflist
External links
Cancer in Dogs: Symptoms, Diagnosis and Treatment
from Pet Education
from Understanding Cancer in Golden Retrievers
Cancer in dogs,