Prevention of Female Cancers by Optimization of Selenium Levels in the Organism.

Inclusion Criteria:

\- Sub-group I - BRCA1 mutation carriers

1. Carrier-status of BRCA1 mutation
2. Age \>20 years
3. Have a breast magnetic resonance imaging and/or ultrasonography and/or mammography that reveals no disease at maximum 9 months after enrollment
4. Be able to give information consent and sign an informed consent form
5. Be willing to comply with all of the study procedures as per the protocol
6. Be willing to inform researchers about current or any new pregnancy
7. Sub-optimal Se level in the blood

Sub-group II - Females from families with hereditary breast cancers but without BRCA1 mutations

1. Age ≥40 years
2. Age ≥20 years for women that have been diagnosed previously with breast cancer
3. Positive medical history of family, matching criteria of hereditary breast/ovarian cancer (HBO) (Appendix 1)
4. No personal history of cancer except for breast cancer and non-melanoma skin cancers
5. Have a breast magnetic resonance imaging/ultrasonography/mammography that reveals no disease at maximum 9 months after enrollment
6. Be able to give information consent and sign an informed consent form
7. Absence of BRCA1 mutations after testing for at least three founder mutations (BRCA1 5382insC, BRCA1 300T/G, BRCA1 4154delA)
8. Be willing to comply with all of the study procedures as per the protocol
9. Be willing to inform researchers about current or any new pregnancy
10. Sub-optimal Se level in the blood

Exclusion Criteria:

Sub-group I - BRCA1 mutation carriers

1. Diagnosis of any previous cancer except for breast cancers and non-melanoma skin cancers
2. Absence of a magnetic resonance imaging/ultrasonography/mammography that reveals no disease at maximum 9 months after enrollment
3. Current pregnancy or breast-feeding
4. Optimal Se level in the blood
5. Age \<20 years
6. Any medical illness, which, in the investigator's opinion, cannot be adequately controlled with appropriate therapy
7. Participation in any other clinical study involving a medical, surgical, nutritional, or life-style intervention (unless individuals are no longer receiving any intervention and they are in the follow-up phase only)

Sub-group II - Females from families with hereditary breast cancers but without BRCA1 mutations

1. Diagnosis of any previous cancer except for breast cancers and non-melanoma skin cancers
2. Absence of magnetic resonance imaging and/or ultrasonography and/or mammography that reveals no disease at maximum 9 months after enrollment
3. Absence of matching pedigree/clinical/molecular criteria of HBO (Appendix 1)
4. Presence of BRCA1 mutation
5. Current pregnancy or breast-feeding
6. Optimal Se level in the blood
7. Age \<40 years except for women that have been previously diagnosed with breast cancer
8. Any medical illness, which, in the investigator's opinion, cannot be adequately controlled with appropriate therapy
9. Participation in any other clinical study involving a medical, surgical, nutritional, or life-style intervention (unless individuals are no longer receiving any intervention and they are in the follow-up phase only)