Veterinary Medicine - March 2008 - (Page 167)

were seen in both dogs, while only one dog experienced reversible peripheral neurotoxicity consisting of rear limb weakness and decreased patellar reexes.8 The anecdotal favorable response observed in the two dogs treated with cisplatin and vindesine, along with this protocol’s acceptable toxicity pro le, warrants further studies examining this combination of chemotherapeutic agents for treating primary lung cancer, especially adenocarcinomas.8 THE FUTURE IN TREATMENT Although complete surgical removal of primary lung tumors before metastasis offers the best hope for a cure, several promising treatment modalities are on the horizon. Intensity-modulated radiation therapy An alternative to conventional lung lobectomy in companion animals is the use of intensity-modulated radiation therapy (IMRT). This treatment modality allows the delivery of curative-intent megavoltage radiation to the neoplastic lesion. Excessive delivery of radiation to normal tissues is minimized by collimating multiple treatment beams in the radiation eld to conform three-dimensionally to the geometry of the cancerous mass.52 In a case study, the effectiveness of IMRT for treating a primary bronchoalveolar carcinoma in a dog was assessed by using positron emission tomography combined with CT. After treatment with IMRT, the dog survived 22 months, only to be euthanized for clinical signs considered unrelated to the primary lung tumor or treatment with IMRT. This anecdotal case report demonstrates favorable clinical outcomes with combination IMRT and positron emission tomography and CT for the treatment and response-assessment of a primary lung tumor in a dog.52 electrode is directly inserted into the tumor percutaneously under the guidance of CT, and alternating electrical currents are passed through the electrode into the neoplastic mass with the intent of inducing tumor cell necrosis. In a study using animal models, transmissible venereal tumor fragments were injected into the lungs of ve dogs, and the patients were subsequently subjected to site-directed RFA. After treatment, the dogs were euthanized, and lung lesions were histologically evaluated. All tumor lesions demonstrated complete thermal coagulative necrosis with no evidence of viable tumor cells. The damage to normal lung parenchyma involved only a narrow zone of hemorrhagic necrosis surrounding each ablated lesion. The ef cacy of RFA on primary pulmonary masses suggests that animals with metastatic pulmonary nodules may also bene t from this treatment modality. Such a supposition is supported by one study in which electrode placement in the epicenter of the cluster of nodules was adequate for complete nodule ablation.53 10. A lateral forelimb radiograph of a geriatric dog presented for evaluation of severe lameness and pain. Note the extreme periosteal proliferation consistent with hypertrophic osteopathy. The dog had a primary pulmonary carcinoma. (Photograph courtesy of Dr. Laura Garrett.) Localized therapy The localized delivery of chemotherapeutic agents or cytokines to the thoracic cavity or lung parenchyma may allow for enhanced anticancer effects within the immediate tumor microenvironment. Radiofrequency ablation Another promising alternative to surgical removal of primary lung tumors is radiofrequency ablation (RFA). A heating Intracavitary chemotherapy. The clinical effectiveness of intracavitary cisplatin administration (50 mg/m2) has been investigated in six dogs with malignant cavitary effusions.54 In three dogs with pleural mesothelioma, complete resolution of cancerous effusions was achieved after a maximum of two treatments. These favorable anecdotal ndings warrant further exploration of intracavitary chemotherapeutic strategies for managing the clinical consequences associated with primary or metastatic lung tumors. A more recent study evaluated the effectiveness of intracavitary mitoxantrone or carboplatin for treating thoracic or abdominal carcinomatosis, sarcomatosis, or mesothelioma in patients with and without malignant effusions. In dogs treated with intracavitary chemotherapy, the median survival time was 332 days, compared with only 25 days in untreated dogs.55 These ndings derived from a small population of cancer-bearing dogs also suggest that intracavitary chemotherapy exerts some bene cial anticancer effects. Inhaled chemotherapy. Although intracavitary chemotherapy may increase the concentration of drug within the pleural space and at the visceral surface of the lung, the attainment of higher drug concentrations within the pulmonary parenchyma is better achieved through inhalation therapy. In a recent study, either doxorubicin or paclitaxel was delivered by aerosolization to 28 dogs with either primary or metastatic pulmonary neoplasia.56 Tumor regression occurred in 25% of dogs treated, with one VETERINARY MEDICINE March 2008 167

Table of Contents Feed for the Digital Edition of Veterinary Medicine - March 2008

Veterinary Medicine - March 2008 Contents Toxicology Brief Idea Exchange A Challenging Case An Update on Diagnosing and Treating Primary Lung Tumors CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - March 2008

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