Illustrated Articles

Dogs + Tumors

  • Many herding breeds (most commonly Collies and Australian Shepherds) have a mutation at the MDR1 gene that makes them more sensitive to the negative effects of certain medications. These drugs include several antiparasitic agents (when given at high doses), the antidiarrheal agent loperamide (Imodium®), and several anticancer drugs. The effects of the mutation vary in severity, depending on whether the dog carries one or two copies of the mutation. There is a cheek swab or a commercially-available test that assesses blood samples for the presence of the MDR1 mutation.

  • The two most common nasal tumors are nasal adenocarcinoma and nasal lymphoma. Clinical signs range from mild to severe, and may include respiratory distress, hemorrhage, and neurological problems. Staging is always recommended before primary therapy is pursued. Radiation therapy is usually pursued for localized disease. Chemotherapy is usually pursued for systemic disease.

  • Neuroendocrine tumors are a group of tumors that develop from the cells of the neuroendocrine system, and include insulinomas, gastrinomas, glucagonomas, carcinoids, medullary thyroid carcinomas, small-cell lung carcinomas, pheochromocytomas, chemodectomas, and Merkel cell carcinomas. Some of these tumors are functional, while others are non-functional. The signs of disease in dogs and cats depend on the type of growth, location of the tumor, its size, the degree of infiltration in the surrounding tissues, whether it has metastasized, and whether it is functional. A definitive diagnosis requires tissue biopsy and histopathology, often with histochemical staining and electron microscopy. Staging is highly recommended for these tumors. Treatment may involve surgery, chemotherapy, radiation therapy, and medical and dietary management.

  • Oral papillomas (warts) are benign tumors of the epithelial lining of the mouth and throat caused by papillomaviruses. The esophagus may also be affected in severe cases.

  • Peripheral odontogenic fibroma (formerly known as fibromatous and ossifying epulis) is a benign, often slow-growing tumor that arises from periodontal structures. They can be further sub-classified as peripheral odontogenic fibromas and acanthomatus ameloblastomas. These tumors do not spread to other organs; however, extension to surrounding tissues is common. Treatment is dependent on size and location of the tumor. If surgery cannot be performed, radiation therapy is an excellent alternative for ameloblastomas given their high degree of response to radiation therapy.

  • Oral squamous cell carcinomas (SCC) are the most common oral tumor in cats, and second most common in dogs. These tumors are locally aggressive, with a possibility to metastasize. Regardless of the location of SCC, surgery is the typically the standard treatment. Radiation therapy may be recommended following surgery or as a primary treatment for palliative care. Staging is recommended for all cases. If metastasis is present chemotherapy is often pursued.

  • Oral fibrosarcomas are the third most common oral tumor in dogs. These tumors arise from the connective tissues of the oral cavity. They are locally aggressive with a low tendency to metastasize. Staging is recommended for oral tumors, and CT imaging is advised for planning treatment, whether surgical or radiation. These tumors may also affect the nasal cavity. Treatment involves surgical removal of the tumorous tissue. Radiation therapy may also be recommended.

  • Like humans, benign and malignant tumors occur in dogs’ mouths. Peripheral odontogenic fibromas (POF) are the most common benign tumors while oral melanomas, squamous cell carcinomas, and fibrosarcomas are the most prevalent malignant tumors in dogs. Diagnosis may be performed via fine needle aspiration or biopsy. Spread to mandibular lymph nodes does occur. Fine needle aspiration of the lymph nodes is recommended when malignant tumors are suspected. Tumor staging including laboratory testing as well as CT imaging helps to plan therapy.

  • Osteosarcoma, or bone cancer, is common in large breed dogs and is very aggressive, with upwards of 90-95% of patients having micrometastasis. Osteosarcoma is very painful. Lameness or a distinct swelling may be noted. Amputation is by far the most common treatment with chemotherapy following surgery. Radiation therapy may also be an option.

  • Ovarian tumors are quite rare in North American pets, mainly due to routine spaying practices. Several types of tumors can arise from the tissues of the ovary. How the tumor will affect your pet is entirely dependent on the location and type of tumor. By far, ovarian cancer is most commonly diagnosed by abdominal ultrasound or during a spay procedure. Full staging is recommended prior to surgery to determine if the cancer has metastasized. Treatment for solitary masses without evidence of spread typically involves ovariohysterectomy. If metastasis is present, chemotherapy should be considered, however its efficacy is not completely known. Without evidence of spread, ovarian tumors carry a good prognosis.