Today's Veterinary Practice

MAY-JUN 2017

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HOW I TREAT 107 MAY/JUNE 2017 ■ TVPJOURNAL.COM we usually attempt to rule out other tumor types with fine-needle aspiration and cytology before surgery. These tumors can spread to local lymph nodes and the lungs, so sampling of local lymph nodes, if palpable, and chest radiography and abdominal ultrasonography are recommended. Computed tomography (CT) can be used to detect smaller lesions in the lungs, but its role in routine staging for mammary cancer has not been determined. The increased expense of CT and requirement for anesthesia may not be cost effective for most patients. Q. What is the current recommended treatment and its prognosis for dogs with mammary carcinoma? A. Surgery is the mainstay of treatment for dogs with mammary carcinoma, with the extent of surgery dependent on the extent of disease. The goal is to remove all existing masses, along with any local, easily accessible lymph nodes. Multifocal disease is common, occurring in more than half of patients. The role of ovariohysterectomy is somewhat controversial, but many oncologists recommend spaying at the time of tumor removal to remove any hormonal inf luence on tumor progression, as well as to eliminate the risk of ovarian and uterine diseases, which are also common in older dogs. Radiation therapy has not found a role in the management of canine mammary carcinoma, although it is a frequent treatment modality in treating breast cancer in people. Chemotherapy has also not been proven to extend survival in veterinary patients in most studies, but it is used frequently in dogs with tumors that have the potential to be aggressive. Doxorubicin, carboplatin, 5-f luorouracil/cyclophosphamide, and toceranib phosphate are some of the more commonly recommended chemotherapeutics. Hormonal modulation therapy (eg, tamoxifen) is not currently recommended in veterinary patients. Prognosis is most inf luenced by tumor type, size, and evidence of metastatic disease ( Box 1 ). Lower-stage disease (<3 cm, no lymphatic invasion or distant metastasis) and well-differentiated tumors are usually associated with survival times measured in years after complete tumor removal. Q. How would a genetic blood test change the diagnosis and treatment for this disease? A. MicroRNAs (miRs) are small, noncoding RNA molecules that can be detected in the blood of cancer patients. If we can identify which miRs are specifically associated with the presence of mammary carcinomas, we may be able to make a diagnosis on the basis of a simple blood test, possibly very early in the course of disease. If we can identify markers associated with more aggressive types and perhaps predict response to treatment, it will inform veterinarians' decision- making about how to manage these patients. BOX 1. Malignant Versus Benign Tumors About half of mammary tumors are benign, and half are malignant. Of those that are malignant, approximately half are likely to metastasize. Large-breed dogs appear to be more predisposed to malignant tumors. A few mutations have been identified in certain breeds and lines of dogs that are similar to mutations found in people, such as in the BRCA1 and BRCA2 genes, which have been shown to increase the incidence of breast and ovarian cancer. Mammary tumors are the most common tumor in intact female dogs, occurring in approximately 25% of this population, with the risk increasing with age.

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