DISEASE CHARACTERISTICS:

• Histologically confirmed non-small cell lung cancer

  • Squamous cell carcinoma
  • Adenocarcinoma (including large cell carcinoma)
  • Non-small cell cancer not otherwise specified

• Brain metastases

  • Biopsy not required
  • Ineligible for surgical resection or radiosurgery
• Systemic disease that is not in immediate need of chemotherapy

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• Karnofsky 70-100%

Life expectancy:

• More than 12 weeks

Hematopoietic:

• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3
• Hemoglobin at least 9 g/dL

Hepatic:

• Bilirubin no greater than 2 times upper limit of normal (ULN)
• SGOT and SGPT no greater than 2 times ULN (5 times ULN if liver metastases present)
• Alkaline phosphatase no greater than 2 times ULN (5 times ULN if liver metastases present)

Renal:

• BUN no greater than 1.5 times ULN
• Creatinine no greater than 1.5 times ULN

Other:

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No known HIV positivity or AIDS-related illness
• No active nonmalignant systemic disease
• No frequent vomiting or other medical condition that would preclude oral medication intake (e.g., partial bowel obstruction)
• No other prior or concurrent malignancies within the past 5 years except surgically cured carcinoma in situ of the cervix or basal cell or squamous cell skin cancer

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• No concurrent immunotherapy or biologic therapy except growth factors

Chemotherapy:

• See Disease Characteristics
• At least 4 weeks since prior chemotherapy and recovered
• No more than 1 prior chemotherapy regimen for systemic metastatic disease
• No prior chemotherapy for brain metastases
• No prior temozolomide
• Concurrent chemotherapy (docetaxel, paclitaxel, or cisplatin) to alleviate progressing systemic disease is allowed

Endocrine therapy:

• Concurrent dexamethasone required

Radiotherapy:

• See Disease Characteristics
• At least 4 weeks since prior radiotherapy to 15% or more of total bone marrow (2 weeks for less than 15% of bone marrow) and recovered
• No prior radiotherapy to 50% or more of total bone marrow
• No prior radiotherapy to the brain
• Prior radiotherapy for local control or palliative therapy for a painful bony lesion allowed
• Concurrent radiotherapy to painful bony lesions allowed if no more than 15% of bone marrow is irradiated

Surgery:

• See Disease Characteristics
• Prior surgery for brain metastases allowed

Other:

• No other concurrent investigational drugs
• Recovered from toxic effects of all prior therapies