Gemcitabine, Docetaxel, and Capecitabine in Treating Patients With Cancer of Unknown Primary Origin

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed malignancy for which no primary origin has been identified despite routine workup, including the following: History and physical examination Chemistry profile and other blood work, including tumor markers with follow up on any positive findings CT scan or MRI of the chest, abdomen, and pelvis Mammography (for female patients) Prostate examination (for male patients) Stool guaiac Measurable disease Previously irradiated lesions are not considered measurable disease unless there is documented clear tumor progression in these lesions after completion of radiotherapy The following tumor types or presentations are excluded: Resectable disease Tumors consistent with germ cell primary, as indicated by any of the following: Midline tumor Elevated beta human chorionic gonadotropin Elevated alpha-fetoprotein i12p chromosomal alteration Prostate primary with elevated prostate-specific antigen Females with axillary nodes as the primary disease site Tumors limited to the peritoneal cavity consistent with primary peritoneal carcinoma Neuroendocrine tumors Squamous cell carcinoma involving cervical or inguinal lymph nodes No symptomatic brain metastases Prior brain metastases allowed provided patient completed definitive treatment with brain irradiation with or without resection PATIENT CHARACTERISTICS: Age 18 and over Performance status ECOG 0-2 Life expectancy More than 3 months Hematopoietic Hemoglobin ≥ 9.0 g/dL Granulocyte count > 1,500/mm^3 Platelet count > 100,000/mm^3 Hepatic Bilirubin normal Meets 1 of the following criteria: Alkaline phosphatase (AP) normal AND AST and ALT ≤ 5 times upper limit normal (ULN) AP ≤ 2.5 times ULN AND AST and ALT ≤ 1.5 times ULN AP ≤ 5 times ULN AND AST and ALT normal Albumin ≥ 3.0 g/dL Renal Creatinine ≤ 1.5 mg/dL Gastrointestinal Able to take oral medication Intestinal absorption intact No uncontrolled diarrhea and/or daily emesis Other Not pregnant or nursing Negative pregnancy test Fertile patients must use effective barrier contraception during and for 3 months after completion of study treatment No other malignancy within the past 5 years except curatively treated carcinoma in situ of the cervix or basal cell skin cancer No severe medical or psychiatric illness that would preclude study treatment No peripheral neuropathy > grade 1 No history of severe hypersensitivity reaction to docetaxel or other drugs formulated with polysorbate 80 PRIOR CONCURRENT THERAPY: Biologic therapy Not specified Chemotherapy No prior chemotherapy for this malignancy Endocrine therapy Not specified Radiotherapy See Disease Characteristics Recovered from prior radiotherapy Prior palliative radiotherapy to areas of bony metastases allowed provided there is measurable disease outside the radiotherapy port At least 4 weeks since prior radiotherapy No prior radiotherapy to ≥ 25% of the bone marrow Surgery See Disease Characteristics Other No concurrent antiviral therapy