Calcitriol and Gefitinib With or Without Dexamethasone in Treating Patients With Advanced Solid Tumors

DISEASE CHARACTERISTICS: * Histologically confirmed advanced solid tumor * Metastatic or unresectable disease * Standard curative or palliative measures do not exist or are no longer effective * No known brain metastases PATIENT CHARACTERISTICS: Age * 18 and over Performance status * ECOG 0-2 OR * Karnofsky 60-100% Life expectancy * More than 3 months Hematopoietic * WBC ≥ 3,000/mm\^3 * Hemoglobin ≥ 8 g/dL * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 Hepatic * Bilirubin normal * AST and ALT ≤ 2.5 times upper limit of normal * No unstable or uncompensated hepatic disease Renal * Creatinine normal OR * Creatinine clearance ≥ 60 mL/min * No prior hypercalcemia * No kidney, ureteral, or bladder stones within the past 10 years * No unstable or uncompensated renal disease Cardiovascular * Ejection fraction ≥ 30% * No heart failure or significant heart disease * No significant arrhythmias * No myocardial infarction within the past 3 months * No unstable angina pectoris * No symptomatic congestive heart failure * No other unstable or uncompensated cardiac disease Pulmonary * No evidence of clinically active interstitial lung disease * Chronic, stable, asymptomatic, radiographic changes allowed * No other unstable or uncompensated respiratory disease Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 30 days after study treatment * Able to receive oral medication * Willing to have serial skin biopsies * No prior allergic reaction to compounds of similar chemical or biological composition to study drugs or other agents used in this study * No ongoing or active infection * No known severe hypersensitivity to gefitinib or any of its excipients * No psychiatric illness or social situation that would preclude study compliance * No other severe or uncontrolled systemic disease or concurrent illness that would preclude study participation * No other significant clinical disorder or laboratory finding that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent filgrastim (G-CSF) or sargramostim (GM-CSF) Chemotherapy * More than 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and recovered Endocrine therapy * No other concurrent systemic glucocorticoid therapy Radiotherapy * More than 4 weeks since prior radiotherapy and recovered Surgery * Recovered from prior major surgery * No prior nephrectomy Other * Recovered from all prior anticancer therapy * More than 30 days since prior non-approved or investigational drugs * More than 7 days since prior thiazides * No concurrent administration of any of the following: * Combination antiretroviral therapy for HIV-positive patients * Phenytoin * Carbamazepine * Barbiturates * Rifampin * Phenobarbital * Hypericum perforatum (St. John's wort) * Calcium supplements * Thiazides * Digoxin * No other concurrent investigational or commercial anticancer agents or therapies