| Exclusion Criteria: | 1) Metastatic Central Nervous System (CNS) from RCC.
2) Subjects who discontinued sunitinib therapy due specifically to intolerance.
3) Bone-only lesions as target lesions.
4) Any prior systemic therapy for RCC/mRCC other than sunitinib.
5) Receiving known strong CYP3A4 isoenzyme inhibitors and/or inducers. Subjects taking CYP3A4 isoenzyme inhibitors and/or inducers not classified as strong are eligible, provided the subject has been on a stable regimen for at least one week prior to randomization.
6) Not recovered from prior biopsy, surgery, traumatic injury, radiation therapy and/or has a non-healing wound or ulcer as judged by the investigator.
7) Grade >/= 3 hemorrhage and/or treatment with transfusions within 2 weeks prior to randomization.
8) Inadequately controlled hypertension (defined as blood pressure of > 140 mm Hg systolic and/or > 90 mm Hg diastolic on treatment).
9) Unstable coronary artery disease, as judged by the investigator, or recent myocardial infarction (< 180 days).
10) American Heart Association (AHA) Class 3/4 heart disease.
11) ECG QTc interval findings > 450 msec for men and > 470 msec for women and/or any uncontrolled clinically significant cardiac arrhythmia.
12) Active ketonuria secondary to poorly controlled diabetes mellitus.
13) History of pulmonary hypertension or interstitial lung disease.
14) Receiving immunosuppressive agents 28 days prior to randomization. Replacement doses of corticosteroids and topical/inhaled steroids are permitted.
15) Immunocompromised subjects, including known seropositivity for human immunodeficiency virus (HIV), or current or chronic hepatitis B and/or hepatitis C infection (as detected by positive testing for hepatitis B surface antigen [HbsAg] or antibody to hepatitis C virus [anti HCV] with confirmatory testing). (Note: testing is not mandatory to be eligible for the study.)
16) Active infection(s), receiving active systemic antimicrobial therapy, or serious intercurrent illness.
17) Current active second malignancy other than non-melanoma skin cancers. Subjects are not considered to have a currently active malignancy if they have completed anti-cancer therapy and are disease-free at least 5 years.
18) Pregnant or nursing women, women who are of childbearing potential (biologically capable of becoming pregnant) who are not using a medically acceptable contraceptive method, or men who are not using a medically acceptable contraceptive method with partners of childbearing potential.
19) Refusal to use medically acceptable contraceptive methods for 3 months after the last dose of temsirolimus or sorafenib therapy.
20) Any other significant illness, residual sunitinib toxicity or medically significant abnormal laboratory finding that would, in the investigator's judgment, make the subject inappropriate for this study, or would increase the risk associated with the subject's participation in this study.
21) Known hypersensitivity to any of the components of the test articles or documented medical condition that would prohibit adequate premedication with antihistamine agents.
22) Patients currently receiving and/or have received prior investigational drugs/vaccines (except sunitinib) within the past 30 days. |