• Subject must currently be receiving enzalutamide for prostate cancer in a study sponsored by Astellas or Medivation and, based on the investigator's assessment, benefit from continued treatment. Subjects participating in investigator-initiated trials are not eligible.

• Subject is able to continue on the treatment regimen that the subject was receiving in the prior study. If in the investigator's assessment, a change is needed to the subject's regimen (e.g., dose change in Androgen deprivation therapy (ADT) or dropping of a combination therapy) approval from a medical monitor is required prior to enrollment.

• Subject is able to swallow enzalutamide capsules and comply with study requirements.

• Subject and female partner who is of childbearing potential must continue to use 2 forms of birth control, of which 1 must be highly effective and 1 must be a barrier method throughout the study and for 3 months after final enzalutamide administration.

• Subject agrees to avoid sperm donation during the study and for at least 3 months after final enzalutamide administration.

• Subject agrees not to participate in another interventional study while on treatment.

⁃ Canada Specific:

• Institutional Review Board (IRB)/Independent Ethics Committee (IEC) approved written Informed Consent and privacy language as per national regulations (e.g., Health Insurance Portability and Accountability Act authorization for the United States sites) must be obtained from the subject prior to any study-related procedures.

• Subject must currently be receiving enzalutamide for breast cancer in a study sponsored by Astellas or Medivation/Pfizer and based on the investigator's assessment, benefit from continued treatment. Subjects participating in investigator-initiated trials are not eligible.

• Subject is able to continue on the treatment regimen that they were receiving in the prior study. If in the investigator's assessment, a change is needed to the subject's regimen (e.g., dropping of a combination therapy) approval from a medical monitor is required prior to enrollment.

• Subject is able to swallow enzalutamide capsules and comply with study requirements.

• Subject is either:

• Of nonchildbearing potential:

• postmenopausal (defined as no spontaneous menses for at least 12 months prior to Day 1 with follicle stimulating hormone (FSH) \> 40 IU/L at Day 1 for women \< 55 years of age),

• documented surgically sterile or status post hysterectomy (at least 1 month prior to Day 1),

• Or, if of childbearing potential,

• must have a negative urine pregnancy test at Day 1 before the first dose of study drug is administered,

• must use 2 acceptable methods of birth control starting at Day 1 and through 6 months after the final study drug administration,

• must not donate ova starting at first administration of study intervention and throughout 6 months after final study intervention administration.

⁃ The 2 acceptable methods of birth control are as follows or per local guidelines where these require additional description of contraceptive methods:

• A barrier method (e.g., condom by a male partner) is required; AND

• One of the following is required:

• Placement of an intrauterine device (IUD) or intrauterine system (IUS);

• Additional barrier method including occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository;

• Vasectomy or other surgical castration at least 6 months before Day 1.

• The subject must not be breastfeeding at Day 1 or during the study period, and for 6 months after the final study drug administration.

• Subject agrees not to participate in another interventional study while on treatment.