TREATMENT
The treatment of choice for solitary primary pulmonary tumors in dogs and cats is wide surgical resection—either a complete
lung lobectomy or a partial lobectomy if the tumor is in the periphery.27,48 However, in cats more often than dogs, even if a single pulmonary nodule is seen radiographically, it is not uncommon to
find multiple small lesions at surgery, suggesting the importance of advanced diagnostic imaging (CT or magnetic resonance
imaging) before surgery.1
Surgery
Given the advent of fiberoptic technologies and the training of surgical residents in noninvasive techniques, thoracoscopic
lung lobectomy is becoming a more common surgical approach for managing lung tumors in companion animals. When compared with
thoracotomy in people, the results of thoracoscopy are less tissue trauma, decreased morbidity, shorter hospitalization, and
earlier return to normal activity.49 Adequate exposure of the thoracic cavity and access to the hilar lymph nodes may still require conventional thoracotomy,
so thoracoscopic procedures are best suited for removing small, peripherally located masses.48
For conventional thoracotomy, a lateral intercostal surgical approach allows access to the primary bronchi for lobectomy of
the side involved but prevents adequate examination of the opposite hemithorax. During thoracotomy, examine and palpate all
accessible lung lobes and tracheobronchial lymph nodes for metastasis or multifocal primary masses. If the tracheobronchial
lymph nodes appear enlarged, they should at least be biopsied and preferentially be extirpated.
Adjuvant chemotherapy
After the primary tumor and associated draining lymph nodes are removed, adjunctive chemotherapy may be warranted based on
host factors (clinical stage) and tumor characteristics (histologic findings). Despite the availability of new chemotherapeutic
drugs, few well-designed prospective studies have investigated the efficacy of one or multiple agents for treating primary
pulmonary neoplasms in dogs and cats.
Vinorelbine, a semisynthetic derivative of vinca alkaloids, has recently been described for treating various neoplasms, including
primary lung tumors, in dogs.50 Vinorelbine is widely distributed in all tissues except for the brain, with concentrations in the lungs reaching 13.8-fold
higher than other vinca alkaloids.51 In one study, two of seven dogs with macroscopic bronchoalveolar carcinoma achieved a partial remission after vinorelbine
treatment. Furthermore, in dogs with microscopic bronchoalveolar carcinoma (incompletely excised primary or lymph node metastases),
vinorelbine's anticancer activity was suggested by the relatively durable survival times of 113, 196, and 730+ days in three
dogs treated with surgery and systemic vinorelbine.50 Further investigations are warranted to determine the effectiveness of adjunctive vinorelbine for treating bronchoalveolar
carcinomas as well as other pulmonary neoplasms in dogs.
In a study of 15 dogs with primary lung tumors treated by lobectomy, five dogs with advanced recurrent pulmonary carcinoma
received one of three chemotherapy protocols: 1) cyclophosphamide, vincristine, and methotrexate, 2) vindesine alone, or 3)
vindesine and cisplatin.8 Two dogs treated with vindesine and cisplatin showed partial responses, with greater than 50% reduction in radiographic
lesions. Anorexia was the only side effect of the cyclophosphamide, vincristine, and methotrexate protocol, while reversible
neurotoxicity was the only side effect of vindesine alone. In the dogs treated with vindesine and cisplatin, mild leukopenia
and gastrointestinal upset were seen in both dogs, while only one dog experienced reversible peripheral neurotoxicity consisting
of rear limb weakness and decreased patellar reflexes.8 The anecdotal favorable response observed in the two dogs treated with cisplatin and vindesine, along with this protocol's
acceptable toxicity profile, warrants further studies examining this combination of chemotherapeutic agents for treating primary
lung cancer, especially adenocarcinomas.8
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