CANCER
Cancer is a complex disease that occurs in all organisms. The causes for cancer are a combination of exposure to environmental carcinogens and the unique genetic make-up of each individual. This is true for Scottish Terriers and all purebred as well as mixed breed dogs.
The following cancers have been reported more commonly in Scotties:
Scottish Terrier Cancers
Urothelial Carcinoma cells under a microscope
Urothelial Carcinoma (UC)
or Transitional Cell Carcinoma (TCC)
Commonly called bladder cancer, urothelial carcinoma develops in the inner layer of cells that line the bladder. These cells are called transitional cells because of their ability to stretch and change shape as the bladder fills. They are responsible for the other name for this disorder, transitional cell carcinoma or TCC. Tumor cells first appear in the lining of the bladder, where they multiply and may invade into deeper layers such as the surrounding muscle. As the bladder tumor gets larger, it occupies more space within the bladder and may grow large enough to obstruct entry of urine from the kidneys into the bladder or to block the urethra, preventing flow of urine out of the bladder. In advanced stages, cancer cells can spread into nearby lymph nodes or potentially into more distant organs such as the liver or lungs.
Generally rare in dogs as a group, Scottish Terriers have an 18-20 times higher risk for TCC than any other breed, strongly suggesting that one or more inherited genes are involved. In addition to a genetic cause, results of ongoing research into TCC suggest that environmental factors such as exposure to pesticides or herbicides as well as chemicals present in air pollution may also increase the risk of TCC in dogs. In humans, smoking is a recognized cause of TCC, raising the possibility that second-hand smoke may also raise a dog’s risk of the disease.
Symptoms of TCC include the appearance of blood in the urine, frequent urination and loss of bladder control. To confirm the diagnosis, a vet will examine the urine to identify the presence of tumor cells and may order the BRAF urine screening test. An ultrasound scan of the bladder will identify the extent and position of a tumor and a biopsy will yield the definitive diagnosis. Although there is no cure as yet, early detection can be key in slowing the cancer’s progression and extending a dog’s survival.
To this end, it is recommended that Scotties have a yearly ultrasound screening starting at 5-6 years of age. TCC is the subject of intense current research, and studies suggest that early intervention with anti-inflammatory drugs, sometimes along with chemotherapy, can significantly slow its progress and lead to longer, symptom-free survival times. Several research studies on TCC and its prevention and control are currently ongoing and receiving grant support from the Health Trust Fund.
Lymphosarcoma cells under a microscope
Lymphosarcoma
Lymphosarcoma, also called lymphoma, is a cancer that usually appears in middle-aged to older dogs. It develops when immune cells called lymphocytes begin to multiply out of control. Lymphoma belongs to a group of cancers called “systemic”, because malignant cells can spread throughout the body, in this case via the lymphatic circulation. Lymphocytes develop in many areas of the body, including small structures called lymph nodes, which are connected to each other by lymphatic vessels that make up a body-wide lymphatic circulation. Because of this, when malignant lymphocytes develop in a lymph node, they can travel easily to other parts of the body. As a result, lymphoma doesn’t usually produce large, easily detectable tumors like other cancers. Sometimes, an owner might feel a small, hard swelling in the neck, armpit, groin or other areas where an enlarged lymph node forms, but often the first sign may be non-specific, such as loss of appetite, lethargy or general weakness. A definitive diagnosis is usually made by aspirating and examining cells from a lymph node or by checking a lymph node biopsy.
Lymphoma is a heterogeneous cancer, meaning it can involve different sub-types of lymphocytes and develop in many different locations. Since it’s also a systemic cancer that affects the entire body, its treatment usually involves chemotherapy, occasionally with radiation added, depending on location and extent of the cancer. Multi-drug therapy, in which two or more chemotherapy drugs are given together, can be especially effective. In most cases, cancer growth slows, with about 90% of dogs responding to treatment and having significantly increased survival times. However, in the majority of cases a dog will eventually become unresponsive to treatment and relapse. In rare cases, called “indolent lymphoma”, disease progression is slow and survival times can reach or exceed two years. Because this is such a heterogeneous cancer, detailed analysis of the specific type of lymphoma by a vet can be very important in determining treatment.
Hemangiosarcoma cells under a microscope
Hemangiosarcoma
Hemangiosarcoma, or HSA, is a cancer that develops when cells that line the heart and blood vessels become malignant and start to multiply. Abnormal growth of these cells produces highly vascular tumors, usually developing in the heart or spleen, although tumors can also develop in any vascular tissue such as muscle or the liver. Usually a cancer of older dogs, in rarer cases HSA may appear in young animals. HSA can be a silent cancer, producing few obvious symptoms until well advanced. In some cases, however, these vascular tumors might bleed periodically, causing subtle signs such as loss of appetite, general weakness or intolerance of exercise. When this cancer develops in the spleen or heart, sudden rupture of the tumor can cause life-threatening problems such as severe weakness or collapse, difficulty breathing or even sudden death. As for many other cancers, the cause of hemangiosarcoma remains unidentified, although a combination of genetics and environmental factors is believed to be involved.
If a vet suspects HSA, imaging with Xrays or ultrasound can confirm the diagnosis. When possible, a biopsy of the tumor can provide additional confirmation. Ideally, early detection and removal of the tumor can be curative. However, in some instances such as HSA in the heart, or when the cancer has already spread, chemotherapy after surgery can destroy remaining cancer cells or, in advanced cases, help prolong life. Radiation therapy may also be used instead of or in addition to chemotherapy. Unfortunately, hemangiosarcoma is an aggressive cancer and most dogs succumb within one year of diagnosis. The Health Trust Fund is currently supporting a research project aimed at improving the outcome of treatments for hemangiosarcoma.
Melanoma cells under a microscope
Melanoma
Melanoma develops when cells called melanocytes multiply abnormally, producing tumors that can appear in a dog’s skin, in his eye or in the oral tissues that line their mouth. Melanocytes get their name from melanin, the pigment they produce that gives dark color to these areas so, not surprisingly, melanoma can develop in the black areas in a Scottie’s mouth, on his tongue, on his toes or in other pigmented places. Rarely, a melanoma may also be pink, without noticeable dark pigment. In the early stages, a melanoma generally produces no symptoms and appears as a small mass which might bleed and break open. Melanoma usually appears in older dogs and, as it grows, the tumor causes varied symptoms, depending on its location. For example, ocular melanoma in the eye can produce vision problems or cause the eye to bulge, while oral melanoma can cause bad breath, drooling, or produce a visible dark mass inside the mouth. Although the cause remains unidentified, a combination of both genetic and environmental factors is believed to be responsible.
Melanoma is generally an aggressive cancer and, once identified, needs immediate treatment. Depending on its location, early removal of the tumor before cancer cells have spread can be curative. Oral melanoma can spread especially quickly and accounts for about 1/3 of all cases. Treatment of this type of disease varies with its location but generally starts with surgery to remove the malignant growth. Melanoma is typically resistant to radiation therapy and no established chemotherapy is available, although a melanoma vaccine exists that may help shrink an existing tumor. In later stages, the cancer can spread to other organs, such as the liver or the lungs, when palliative care such as pain relievers, steroids and nutritional support can be helpful.
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