Maintaining Suppression of Testosterone With Transdermal Estradiol Gel

Inclusion Criteria: 1. Males, Ages 18 and older 2. Body Mass Index (BMI) between 18 and 35 kg/m2 (inclusive) 3. Not currently hospitalized 4. Clinical indication of adenocarcinoma of the prostate evidenced by a biopsy report on record 5. At present receiving ADT treatment with a GnRH agonist for at least 2 months but not longer than 36 months without interruption - Note: If the patient received GnRH agonist treatment prior to the treatment described under 5, there must be evidence of a period without GnRH agonist treatment for a minimum of 2 months prior to starting the present treatment as is seen, for example with intermittent treatment regimens. 6. Able to initiate Screening procedures 2 weeks prior to the next scheduled injection with a GnRH agonist 7. Willing to discontinue current ADT regimen for the duration of the study 8. T level less than 50 ng/dL at Screening 9. WHO/ECOG performance status of 0 or 1 10. Life expectancy of at least 1 year 11. Adequate renal function demonstrated by having normal blood urea nitrogen (BUN) and Creatinine Screening lab values Exclusion Criteria: 1. History or presence of allergic or adverse response to estradiol 2. Presence of symptomatic metastatic disease, risk of spinal cord compression or urinary obstruction 3. History within the past 2 years of deep vein thrombosis (DVT), pulmonary embolism (PE2), a known thrombophilic disorder (eg.protein C, protein S, or antithrombin deficiency), or cerebrovascular accident (CVA) 4. History within the past 2 years of myocardial infarction or a coronary vascular procedure (e.g. percutaneous coronary intervention, coronary artery bypass graft) 5. History of congestive heart failure 6. Use of any investigational drug, biologic, or device within 28 days prior to the first dose of study gel 7. Use of any of the following known inducers or inhibitors of cytochrome P450 3A4 (CYP3A4): phenobarbital, carbamazepine, rifampin, erythromycin, clarithromycin, ketoconazole, itraconazole, ritonavir, St. John's Wort preparations (Hypericum perforatum), and grapefruit juice 8. Hematological parameters (Hematocrit or Hemoglobin) outside 20% of the upper or lower limits of normal at Screening 9. Active skin rash, sunburn, or other skin disorder on the upper arm(s) that requires treatment or may affect skin absorption of study gel 10. Resting uncontrolled hypertension (HTN) (160/100 mmHg) at Screening 11. Co-existent malignancy or a history of malignancy during the past 5 years, with the exception of basal and/or squamous cell carcinoma of the skin 12. Any other significant concurrent illness or disease or condition that in the opinion of the Investigator might interfere with the patient's ability to receive the treatment outlined in the protocol or might put him at additional risk