Statement: Patients with cancer in situ of the cervix are eligible for the primary trial and the secondary trial.
Primary_evidence: Inclusion Criteria:   Women 18 years of age or older   History of invasive ER+ or PR+ breast cancer treated with at least 4.5 years of tamoxifen   No current evidence of recurrent invasive disease or metastatic disease. Patients may have a history of bilateral breast cancer   Premenopausal (estradiol level in premenopausal range, >20pg/ml, within the prior 28 days)   Liver function tests and creatinine <2.5 times the upper limit of normal within the 28 days prior to enrollment   ECOG Performance Status 0-1   Must agree to use non-hormonal contraception (condoms, diaphragm, IUD, sterilization, abstinence, etc) and no other hormonal therapy during trial and until 3 months after letrozole is stopped   Negative pregnancy test within 14 days prior to enrollment   Patient must be able to speak, read and write in English Exclusion Criteria:   Previous treatment with an oral or IV bisphosphonate in the prior two years   History of cancer other than breast cancer within 5 years excluding basal/squamous cell skin carcinoma in situ of the cervix   Women with evidence of current local recurrence or metastatic breast cancer   Pregnant women   Nursing women   Women who are currently taking tamoxifen and are unwilling to stop this medication   Women with a known deleterious BRCA 1 or BRCA 2 mutation
Secondary_evidence: Inclusion Criteria:   Females greater than or equal to (  ) 18 years of age, with histologically-confirmed HER2-positive breast cancer   Metastatic breast cancer, with progression on trastuzumab-based therapy as last treatment for metastatic disease   Less than or equal to (  ) 3 chemotherapy regimens prior to study entry   Last trastuzumab dose 9 weeks before study entry for participants receiving pertuzumab + trastuzumab, and 4 weeks for participants receiving pertuzumab monotherapy   Left ventricular ejection fraction 55% at study entry Exclusion Criteria:   Previous treatment with an anti-cancer vaccine or any targeted therapy other than trastuzumab   Brain metastases   History of any cardiac adverse event related to trastuzumab therapy   Any other malignancy in the last 5 years, except for basal cell cancer or cancer in situ of the cervix