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OBJECTIVE: To determine associations between clinical and histologic factors in dogs with primary lung tumors and outcome and to develop a histologic grading method for primary lung tumors. DESIGN: Retrospective study. ANIMALS: 67 dogs undergoing thoracotomy and lobectomy for primary lung tumors. PROCEDURE: Medical records and histologic sections were reviewed to evaluate factors of prognostic importance. Association of these factors with disease-free interval (DFI) and survival time was evaluated, using the Cox proportional hazards model. Median DFI and survival time were determined, using the Kaplan-Meier product-limit method. RESULTS: Clinical and histologic factors significantly associated with prognosis were histologic score, detection of clinical signs, and metastasis to regional lymph nodes. On the basis of histologic score, a histologic grading method was developed. Dogs with well-differentiated tumors had significantly longer survival time and DFI (median DFI, 493 days) than dogs with moderately (median DFI, 191 days) or poorly (median DFI, 0 days) differentiated tumors. Dogs with clinical signs or metastasis to regional lymph nodes had shorter survival times and DFI than dogs in which lung masses were discovered as an incidental finding. CLINICAL IMPLICATIONS: Dogs with well-differentiated, nonmetastasized, primary lung tumors that do not have clinical signs associated with the tumor have a favorable prognosis. Dogs with more advanced disease or aggressive tumors histologically may require treatment, such as chemotherapy in combination with surgery. The grading method proposed here for primary lung tumors may be useful in other dogs with primary lung tumors.
McNiel et al. (Mon,) studied this question.