RATIONALE: Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die.

PURPOSE: Phase II trial to study the effectiveness of R115777 in treating patients who have relapsed or refractory multiple myeloma.

OBJECTIVES: I. Determine the rate of objective response and disease stabilization in patients with relapsed or refractory multiple myeloma treated with R115777. II. Determine whether the degree of inhibition of FTase activity and farnesylation of lamin-B, H-, K-, and N-RAS in peripheral blood mononuclear cells and tumor tissue correlates with tumor response in patients treated with this regimen. III. Determine whether the presence of activating RAS mutations in myeloma cells predicts treatment response in patients treated with this regimen. IV. Correlate R115777 plasma levels and RAS mutation status with tumor response in patients treated with this regimen.

OUTLINE: Patients receive oral R115777 twice daily on days 1-21. Treatment repeats every 28 days in the absence of disease progression or unacceptable toxicity. Patients are followed for at least 30 days.

PROJECTED ACCRUAL: Approximately 12-42 patients will be accrued for this study within 25 months.

DISEASE CHARACTERISTICS: Diagnosis of relapsed or refractory multiple myeloma confirmed by the presence of the following: Bone marrow plasmacytosis with at least 10 percent plasma cells Sheets of plasma cells OR Biopsy-proven plasmacytoma Documentation of at least one of the following criteria: Serum myeloma (M)-protein component at least 1.0 g/dL by serum protein electrophoresis Urine M-protein excretion more than 200 mg/24 hours by urine protein electrophoresis Stage IIA or IIIA disease Measurable disease The following are not considered measurable disease: Lytic bone lesions Anemia Bone marrow plasmacytosis Beta-2 microglobulin in serum Previously treated with conventional chemotherapy Progressing or relapsing disease at time of study

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Eastern Cooperative Oncology Group (ECOG) 0-3 Life expectancy: More than 8 weeks Hematopoietic: Absolute neutrophil count at least 1,000/mm^3 Hepatic: aspartate aminotransferase (AST) or alanine transaminase (ALT) no greater than 2 times upper limit of normal (ULN) Bilirubin no greater than 2 mg/dL Renal: Creatinine no greater than 1.5 times ULN Calcium no greater than 12 mg/dL Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception Capable of swallowing intact study medication tablets No concurrent serious infection No grade 3 or greater peripheral neuropathy No life-threatening illness unrelated to tumor No other active or invasive cancer within the past 3 years except nonmelanoma skin cancer

PRIOR CONCURRENT THERAPY: Biologic therapy: Prior thalidomide allowed At least 14 days since prior immunologic agents No concurrent immunologic agents Chemotherapy: See Disease Characteristics At least 3 weeks since prior cytotoxic chemotherapy No other concurrent cytotoxic therapy Endocrine therapy: At least 14 days since prior high-dose corticosteroids No concurrent hormonal therapy No concurrent corticosteroids Radiotherapy: At least 3 weeks since prior radiotherapy and recovered No concurrent radiotherapy Surgery: Not specified Other: No other concurrent cancer therapy Concurrent pamidronate or other bisphosphonates allowed