DISEASE CHARACTERISTICS: Histologically confirmed small cell lung cancer Must have received one prior chemotherapy regimen and relapsed OR Diagnosis of metastatic breast cancer No more than two prior chemotherapy regimens for metastatic disease Measurable disease Prior radiotherapy to measurable lesion allowed if progressed since treatment No diffuse bone marrow involvement on OctreoScan scintigraphy Positive for somatostatin receptors (grade 3 or 4) by Octreoscan scintigraphy No unstable brain metastases within the past 6 months Hormone receptor status: Not specified

PATIENT CHARACTERISTICS: Age: 18 and over Sex: Male or female Menopausal status: Not specified Performance status: Small cell lung cancer patients:

Karnofsky 80-100% Breast cancer patients: Karnofsky 50-100% Life expectancy: Greater than 12 weeks Hematopoietic: Hemoglobin at least 8 g/dL Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) AST and ALT no greater than 5 times ULN Renal: Creatinine no greater than 1.7 mg/dL OR Creatinine clearance at least 40 mL/min Cardiovascular: No history of congestive heart failure unless ejection fraction at least 40% Other: No other significant, uncontrolled medical, psychiatric, or surgical condition that would preclude study Not pregnant No nursing during and for 1 month following study Negative pregnancy test Fertile patients must use effective contraception during and for 6 months following study

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior biologic therapy No concurrent biologic therapy Chemotherapy: See Disease Characteristics At least 4 weeks since prior chemotherapy No concurrent chemotherapy Endocrine therapy: At least 2 weeks since prior hormonal therapy Radiotherapy: See Disease Characteristics At least 2 weeks since prior radiotherapy Concurrent localized radiotherapy allowed provided measurable disease exists outside of the radiation field Surgery: At least 2 weeks since prior surgery Concurrent localized surgery allowed provided measurable disease exists outside of the surgical field Other: At least 4 weeks since other prior investigational therapy No concurrent medication that decreases renal function (e.g., aminoglycoside antibiotics) No other concurrent investigational agent Concurrent bisphosphonates allowed