This is a randomized phase III trial comparing cisplatin with or without gemcitabine in patients with carcinoma of unknown primary and a predicted favorable prognosis.

The purpose of this trial is to compare the overall survival rates of patients with carcinoma of unknown primary (CUP) and a predicted favorable prognosis according to the French classification treated with cisplatin with or without gemcitabine.

Inclusion Criteria:

• Patients older than 18 years
• Evidence of CUP based on histologic examination
• Negative search for the primary tumor site using recommended guidelines
• Disease classified as good prognosis according to the French classification criteria: *performance status >2 and *normal serum LDH
• No prior chemotherapy
• No previous carcinoma, except basal-cell carcinoma of the skin
• Adequate renal function: measured or calculated creatinine clearance > 60 ml/min
• Absolute granulocyte count ≥ 1,500/mm3; platelets ≥ 100,000 mm3; bilirubin ≤ 1.5 fold the upper normal value
• Signed informed consent

Exclusion Criteria:

• Patients infected by the Human Immunodeficiency Virus (HIV)
• CUP belonging to one of the following subgroups: 1) Axillary lymph node of an adenocarcinoma in a woman; 2) Serous adenocarcinoma of the peritoneum in a woman; 3) Undifferentiated carcinoma of the middle line in a young man; 4)Squamous-cell carcinoma; 5) Neuroendocrine carcinoma; 6) Bone metastases with elevated serum prostate specific antigen (PSA) in a man
• Patients who do not fit inclusion criteria.