Inclusion Criteria:

1. History of histologically confirmed diagnosis of borderline tumors or low-grade epithelial cancer from the ovary, fallopian tube or primary peritoneum. Eligible histologies include borderline serous papillary, borderline mucinous papillary, borderline endometrioid, low-grade serous papillary, low-grade mucinous papillary, low-grade endometrioid and mixture of the above. Patients whose tumors are histologically borderline but have low grade invasive implants are also included. Patients whose tumors are histologically borderline but which include high grade components are excluded.
2. Recurrent or advanced borderline or low-grade epithelial ovarian, fallopian tube or primary peritoneal tumors not amenable to surgery, or patients who have measurable residual disease at the end of secondary cytoreduction.
3. The ovarian tumors have to be either estrogen receptor or progesterone receptor positive.
4. Measurable disease by radiological imaging studies. Raised CA125 tumor marker alone and lesions located in previously irradiated areas are not considered measurable.
5. Age greater than 18 years of age.
6. Expected survival of more than 12 weeks.
7. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
8. Willingness to comply with study procedures and follow up examinations.
9. Have written informed consent. (Signature on consent form indicating that the patient is aware of the nature of her disease and willingly gives written consent after being informed of the procedure to be followed, the experimental nature of the therapy, alternative treatment options and potential benefits and risks associated with the therapy).
10. Known history of Central nervous system metastases allowed if patients have had treatment, are neurologically stable, and do not require oral or intravenous steroids or anti-convulsants, provided brain scan (Computer Assisted Tomography or Magnetic Resonance Imaging Scans) shows absence of active disease.
11. Have adequate bone marrow reserve as indicated by absolute neutrophil count (ANC)> 1,500/ mm3; platelet count > 100,000/mm3; hemoglobin > 9.0g/dL.
12. Have adequate liver function tests as indicated by bilirubin < 1.5 X normal, alanine amino-transferase (ALT)< 3 X normal; and aspartate amino-transferase (AST) < 3 X normal.
13. Have adequate renal function tests as indicated by serum creatinine of < 1.5mg/dl.

Exclusion Criteria:

1. Failure to recover from any prior surgery or major surgery within 4 weeks of study entry
2. Patients with sarcomatous, germ cell or stromal elements in their cancers are not eligible.
3. Patients with intermediate and high-grade primary ovarian, fallopian tube, and primary peritoneal epithelial carcinoma. Patients whose tumors are histologically borderline but which includes high grade components are excluded.
4. Pregnant or lactating women
5. Leptomeningeal or carcinomatous meningitis
6. Unstable medical conditions such as uncontrolled cardiac arrythmia or history of myocardial infarction within 6 months
7. Any severe, concurrent disease, infection or co-morbidity that, in the judgment of the investigator, would make the patient inappropriate for study entry.
8. Any signs of intestinal obstruction interfering with nutrition
9. Treatment with chemotherapy, radiotherapy, radiopharmaceuticals or immunotherapy within 4 weeks of first study dosing with letrozole (within 6 weeks for nitrosureas or mitomycin C) or failure to recover from the toxic effects of any of these therapies prior to study entry.
10. Patients with more than 4 prior chemotherapy regimes with all platinum regimes counted as one.
11. Patients who has had prior anti-cancer hormonal therapy for ovarian cancer with aromatase inhibitors. Patients treated with gonadotrophin agonist, gonadotropin antagonist and SERMS are allowed. Patients on hormone replacement therapy or who have had fertility treatment with estrogens and gonadotropins are also allowed.
12. Patients on estrogen and progesterone replacement therapy must have a wash out period of 4 weeks.
13. A history of prior malignancy except for adequately treated carcinoma in situ of the cervix, basal cell or squamous cell skin cancer, or other cancer for which the patient has not been disease- free for at least five years
14. Patients receiving concurrent chemotherapy, radiotherapy or immunotherapy.
15. Participation in any investigational drug study within 30 days of the first day of dosing.
16. Psychiatric disorders that would preclude obtaining informed consent and participation in an ongoing research study
17. Patients with a known history of human immunodeficiency virus (HIV) infection
18. Patients with inadequately treated serious thromboembolic disease such as pulmonary embolism and deep vein thrombosis, or with known clotting disorders.