Ribociclib and Letrozole in Treating Patients With Relapsed ER Positive Ovarian, Fallopian Tube, Primary Peritoneal, or Endometrial Cancer

Patients who have central nervous system (CNS) involvement unless they meet ALL of the following criteria:

* \>= 4 weeks from prior therapy completion (including radiation and/or surgery) to starting the study treatment

* Clinically stable CNS tumor at the time of screening and not receiving steroids and/or enzyme-inducing anti-epileptic medications for brain metastases

Patient has any other concurrent severe and/or uncontrolled medical condition that would, in the investigator's judgment, cause unacceptable safety risks, contraindicate patient participation in the clinical study or compromise compliance with the protocol (e.g. chronic pancreatitis, chronic active hepatitis, active untreated or uncontrolled fungal, bacterial or viral infections, etc.)

Clinically significant, uncontrolled heart disease or cardiac repolarization abnormalities and/or recent events including any of the following:

* History of acute coronary syndromes (including myocardial infarction, unstable angina, coronary artery bypass grafting, coronary angioplasty, or stenting) or symptomatic pericarditis within 6 months prior to screening

* History of documented congestive heart failure (New York Heart Association functional classification III-IV)

* Documented cardiomyopathy

* Left ventricular ejection fraction (LVEF) \< 50% as determined by multiple gated acquisition (MUGA) scan or echocardiogram (ECHO) at screening

* Clinically significant cardiac arrhythmias (e.g. ventricular tachycardia), complete left bundle branch block, high-grade atrioventricular (AV) block (e.g. bifascicular block, Mobitz type II and third-degree AV block) long QT syndrome or family history of long QT syndrome

* Idiopathic sudden death or congenital long QT syndrome

* Risk factors for torsades de pointe (TdP) including uncorrected hypokalemia or hypomagnesemia, history of cardiac failure, or history of clinically significant/symptomatic bradycardia

* Concomitant use of medication(s) with a known risk to prolong the QT interval and/or known to cause torsades de pointe that cannot be discontinued (within 5 half-lives or 7 days prior to starting study drug) or replaced by safe alternative medication

* Inability to determine the QT interval on screening (corrected QT interval \[QTcF\], using Fridericia's correction)

* Systolic blood pressure (SBP) \> 160 mmHg or \< 90 mmHg at screening

* Bradycardia (heart rate \< 50 at rest), by electrocardiogram (ECG) or pulse, at screening

* Tachycardia (heart rate \> 110 at rest), by ECG or pulse at screening

Inability to determine the QTcF interval on the ECG (i.e.: unreadable or not interpretable) or QTcF \> 450 msec (using Fridericia's correction); NOTE: all as determined by screening ECG

Patient is currently receiving any of the following medications and cannot be discontinued =\< 7 days prior to starting study drug: known strong inducers or inhibitors of cytochrome P450 family 3, subfamily A, polypeptide 4/5 (CYP3A4/5) including grapefruit, grapefruit hybrids, pummelos, star-fruit, and Seville oranges or that have a narrow therapeutic window and are predominantly metabolized through CYP3A4/5 or herbal preparations/medications or dietary supplements

Patient is currently receiving or has received systemic corticosteroids within =\< 2 weeks prior to starting study drug, or who have not fully recovered from side effects of such treatment; NOTE: the following uses of corticosteroids are permitted: single doses, topical applications (e.g., for rash), inhaled sprays (e.g., for obstructive airways diseases), eye drops or local injections (e.g., intra-articular)

Patient has received radiotherapy =\< 4 weeks or limited field radiation for palliation =\< 2 weeks prior to starting study drug, and who has not recovered to grade 1 or better from related side effects of such therapy (exceptions include alopecia) and/or in whom \>= 30% of the bone marrow was irradiated

Patient has had major surgery =\< 14 days prior to registration or has not recovered from major side effects (tumor biopsy is not considered as major surgery)

Known to be human immunodeficiency virus (HIV) positive (testing not mandatory)

Patient has a known hypersensitivity to any of the excipients of ribociclib

Patient is currently receiving warfarin or other Coumarin-derived anticoagulant for treatment, prophylaxis or otherwise; NOTE: therapy with apixaban, dabigatran, heparin, low molecular weight heparin (LMWH) or fondaparinux is allowed

Participation in a prior investigational study within 30 days prior to enrollment or =\< 5 half-lives of the investigational product, whichever is longer

Patient has not recovered from all toxicities related to prior anticancer therapies to National Cancer Institute (NCI)-Common Terminology Criteria for Adverse Events (CTCAE) version 4.0 grade \< 3 (exception to this criterion: patients with any grade of alopecia or neuropathy are allowed to enter the study)

Patient with a Child-Pugh score B or C

Patient has impairment of gastrointestinal (GI) function or GI disease that may significantly alter the absorption of the study drugs (e.g., ulcerative diseases, uncontrolled nausea, vomiting, diarrhea, malabsorption syndrome, or significant small bowel resection)

Prior therapy with ribociclib or an aromatase inhibitor (letrozole, anastrozole or exemestane)

Patient has received systemic chemotherapy =\< 3 weeks prior to registration

What this study is about