Octreotide With or Without Prednisone in Treating Patients With Metastatic or Recurrent Thymoma

DISEASE CHARACTERISTICS: Histologically confirmed invasive, recurrent, or metastatic thymoma or thymic carcinoma not amenable to potentially curative therapy Must have extensive disease defined as: - distant disease - pleural disease with or without mediastinal involvement - recurrent progressive disease in site of previous radiotherapy Measurable disease with at least one bidimensionally measurable lesion Must have octreotide scan prestudy that demonstrates activity in the area of measurable disease within 6 months prior to registration PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-1 Life expectancy: Not specified Hematopoietic: Not specified Hepatic: Bilirubin no greater than 2.0 mg/dL Renal: Creatinine no greater than 3.0 mg/dL Other: No diabetes mellitus or any other complications to high dose corticosteroid therapy No acute concurrent complications such as infections Other prior malignancy(ies) must have been curatively treated and demonstrate no evidence of recurrence Not pregnant or nursing Negative pregnancy test Adequate contraception required of all fertile patients PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Prior chemotherapy allowed if disease progression is demonstrated prior to study entry Endocrine therapy: Prior or concurrent corticosteroids for myasthenia gravis allowed Radiotherapy: Prior radiotherapy allowed Surgery: No postsurgical complications