Thymoma in dogs: 23 cases (1980-1991)
Atwater, S.W.; Powers, B.E.; Park, R.D.; Straw, R.C.; Ogilvie, G.K.; Withrow, S.J.
Journal of the American Veterinary Medical Association 205(7): 1007-1013
1994
ISSN/ISBN: 0003-1488 PMID: 7852153 Document Number: 429742
Medical records of 23 dogs in which thymoma was diagnosed between Jan 1, 1980 and Dec 31, 1991 were reviewed. All thymomas were in the cranial mediastinum. 11 dogs had megaoesophagus, and myasthenia gravis was confirmed in 7 of these. One dog developed clinical signs of myasthenia gravis after removal of the thymoma. Concurrent, nonthymic neoplasms were found in 5 dogs, and 2 had hypercalcaemia. Three dogs developed third-degree atrioventricular heart block, 1 of which had generalized myositis involving the cardiac muscle. None of the dogs had evidence of distant metastasis. Histologically, the predominant tumour types were differentiated epithelial type (9/23) and lymphocyte-rich type (6/23). Clear cells (large cells with nonstaining cytoplasm) comprised >= 50% of the cell population in tumours from 5 dogs. Mast cells were detected histologically in 85% of thymomas evaluated. 16 dogs were treated, and in 15 of these, surgery was the primary means of treatment. Six of the 9 dogs with megaoesophagus that underwent surgery died or were destroyed within a week of diagnosis; whereas only 1 of the 4 dogs without megaesophagus that underwent surgery died within 1 week of diagnosis. Two dogs underwent surgery and received adjuvant chemotherapy. One dog died of complications associated with chemotherapy. One dog was treated with chemotherapy alone and survived 14 months. Seven dogs did not undergo treatment; 4 of these were destroyed immediately after the mass was first discovered. By means of univariate analysis, age (<= 8 years old vs > 8 years old), megaoesophagus (present vs not present), and histological type were associated with survival time. Only megaoesophagus was associated with survival time by multivariate analysis. Dogs with megaoesophagus had a Kaplan-Meier median survival time of 4 days. Kaplan-Meier median survival time for dogs without megaesophagus could not be calculated, because most dogs died of causes unrelated to the thymoma. Kaplan-Meier 1-year survival rate was 83% for dogs without megaesophagus.