Temozolomide in Treating Patients With Invasive Pituitary Tumors

DISEASE CHARACTERISTICS: * Clinically demonstrable invasive pituitary macroadenoma, including any of the following subtypes: * Growth hormone-secreting * Prolactin-secreting * Adrenocorticotrophic hormone-secreting * Non-secreting * Must have biochemical evidence of any of the following: * Acromegaly as measured by serum insulin-like growth factor-1 (IGF-1) * Prolactinoma as measured by serum prolactin (PRL) * Cushing's disease as measured by 24-hour urinary-free cortisol * Inadequate tumor control, defined as a visible pituitary tumor ≥ 1 cm in maximal diameter encasing the carotid arteries, and/or invading into the cavernous sinuses, and/or abutting/invading the optic chiasma as demonstrated by MRI scan with or without contrast * Previously assessed by radiosurgery and meets ≥ 1 of the following criteria: * Not a suitable candidate for radiotherapy (e.g., tumor abutting and/or invading the optic chiasm) * Declined radiotherapy (in light of side effects or personal choice) * Has not exhibited tumor shrinkage or tumor continues to grow ≥ 1 year after completion of radiotherapy * Must have a normal visual field evaluation by Goldman perimetry * No visual field abnormalities * Hypopituitarism allowed as evidenced by any or all of the following: * Subnormal growth hormone response to arginine/growth hormone-releasing hormone testing (normal response is an increase of \> 4 ng/mL) * Low age- and sex-matched IGF-1 levels * Low thyroid-stimulating hormone (TSH), free triiodothyronine (T3), and free thyroxine (T4) levels * Low estradiol levels * Low luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels in postmenopausal female patients OR low testosterone, LH, and FSH levels in male patients * Serum cortisol \< 3 ng/mL (at 8 am) * Patients diagnosed with hypopituitarism (except for post-menopausal females) are required to initiate hormone replacement therapy for the 12-month duration of the study and to discontinue hormone replacement therapy at the end of 12 months to re-evaluate hypopituitarism PATIENT CHARACTERISTICS: * Able to undergo a pituitary MRI scan * No clinically significant renal, hematologic, or hepatic abnormalities * No prior or concurrent medical condition that may interfere with the conduct of the study or the evaluation of its results, in the opinion of the Investigator or the Data Safety Monitoring Board compliance officer * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception for ≥ 2 months prior to, during, and for 1 month after completion of study therapy * No history of immunocompromise, including known HIV positivity as measured by enzyme linked immunosorbent assay (ELISA) and western blot * No alcohol or drug abuse within the past 6 months * No blood donation within the past 2 months * No history of noncompliance to medical regimens, potential unreliability, or inability to complete the entire study * No other active malignant disease within the past 5 years, except basal cell carcinoma or carcinoma in situ of the cervix * No active or suspected acute or chronic uncontrolled infection PRIOR CONCURRENT THERAPY: * See Disease Characteristics * Prior pituitary surgery allowed provided the surgery failed to induce complete tumor response and the patient is deemed unsuitable for further pituitary surgeries * At least 3 months since prior pituitary surgery * More than 1 month since prior unlicensed drugs or participation in a clinical trial with an investigational drug * No concurrent pituitary surgery or pituitary radiotherapy * No other concurrent therapy to reduce pituitary tumor size