Inclusion Criteria:

• - OSA SCREENING ELIGIBILITY CRITERIA: Documented diagnosis of essential thrombocythemia or polycythemia vera by either 2008 WHO criteria or 2016 WHO Criteria prior to screening.

• - OSA SCREENING ELIGIBILITY CRITERIA: For subjects receiving therapy for PV or ET (i.e. hydroxyurea, peginterferon, etc.): Patients must be on a stable dose for >= 28 days prior to study entry and expected to remain on a stable dose for the duration of trial participation.

It is anticipated that during the 6 month duration of study, there will not be any dose modification of hydroxyurea or interferon and this will be communicated to treating providers and patient during enrollment into the trial. However, clinically indicated dose modification of PV/ET therapy while on trial will not necessitate CPAP study discontinuation.

• - OSA SCREENING ELIGIBILITY CRITERIA: Subject must have =< 20.0 pack-year smoking history OR have quit smoking => 3 years ago and do not have any current symptoms of COPD and/or have normal pulmonary function tests.

• - OSA SCREENING ELIGIBILITY CRITERIA: Eastern Cooperative Oncology Group (ECOG) performance status 0-2.

• - OSA SCREENING ELIGIBILITY CRITERIA: Negative serum or urine pregnancy test at screening for women of childbearing potential.

• - OSA SCREENING ELIGIBILITY CRITERIA: Highly effective contraception for both male and female subjects from study enrollment through treatment, and for at least 3 months after last study treatment administration if the risk of conception exists.

• - OSA SCREENING ELIGIBILITY CRITERIA: Able to provide informed consent and willing to sign an approved consent form that conforms to federal and institutional guidelines.

• - OSA SCREENING ELIGIBILITY CRITERIA: Able to read and complete required study questionnaires.

• - TREATMENT ELIGIBILITY CRITERIA: Eligible for OSA Screening Component portion of this trial.

• - TREATMENT ELIGIBILITY CRITERIA: Diagnosed OSA with Sleep Study score >= 5.

• - TREATMENT ELIGIBILITY CRITERIA: Snoring, Tiredness, Observed Apnea, Blood Pressure, Body Mass Index, Age, Neck Circumference and Gender (STOP-BANG) screening questionnaire score >= 3.

• - TREATMENT ELIGIBILITY CRITERIA: Willingness to comply with required CPAP compliance rate of >= 4hrs/day for 70% of days over 6 months of CPAP treatment.

• - TREATMENT ELIGIBILITY CRITERIA: Able to provide informed consent and willing to sign an approved consent form that conforms to federal and institutional guidelines.

Exclusion Criteria:

• - OSA SCREENING ELIGIBILITY CRITERIA: Use of JAK2 inhibitors within 6 months prior to registration.

• - OSA SCREENING ELIGIBILITY CRITERIA: Previous or current use of TNF inhibitors.

• - OSA SCREENING ELIGIBILITY CRITERIA: Prior substantial, prolonged use of CPAP or alternative therapy for OSA, including oxygen.

No more than 6 monthsof continuous therapy with CPAP in the last 5 years will be allowed.

• - OSA SCREENING ELIGIBILITY CRITERIA: Autoimmune disease requiring concurrent use of immunomodulatory, including rheumatologic disorders.

• - OSA SCREENING ELIGIBILITY CRITERIA: Prior invasive cancer (except nonmelanoma skin cancer) unless disease free for at least 2 years or life expectancy without treatment is greater than 2 years, e.g., low risk localized prostate cancer.

• - OSA SCREENING ELIGIBILITY CRITERIA: The subject has uncontrolled, significant intercurrent or recent illness including, but not limited to, the following conditions: - Cardiovascular disorders: - Congestive heart failure New York Heart Association class 3 or 4, unstable angina pectoris, serious cardiac arrhythmias.

• - Uncontrolled hypertension defined as sustained blood pressure (BP) > 150 mm Hg systolic or > 100 mm Hg diastolic despite optimal antihypertensive treatment.

• - Stroke (including transient ischemic attack [TIA]), myocardial infarction (MI), or other ischemic event, or thromboembolic event (e.g., deep venous thrombosis, pulmonary embolism) within 6 months of screening.

Patients receiving anti-coagulant therapy for previous thromboembolic event will be allowed to enroll on study.

• - Other clinically significant disorders that would preclude safe study participation.

• - End stage Renal disease.

• - Advanced liver disease such as cirrhosis, chronic active hepatitis or chronic persistent hepatitis.

• - Active (acute or chronic) or uncontrolled severe infection.

• - OSA SCREENING ELIGIBILITY CRITERIA: Known history of human immunodeficiency virus (HIV), chronic hepatitis B virus (HBV), or hepatitis C virus (HCV) infection.

• - TREATMENT ELIGIBILITY CRITERIA: Use of JAK2 inhibitors within 6 months of registration.

• - TREATMENT ELIGIBILITY CRITERIA: Previous or current use of TNF inhibitors.

• - TREATMENT ELIGIBILITY CRITERIA: Prior use of CPAP or alternative therapy for OSA, including oxygen.

• - TREATMENT ELIGIBILITY CRITERIA: Autoimmune disease requiring concurrent use of immunomodulatory, including rheumatologic disorders.

• - TREATMENT ELIGIBILITY CRITERIA: Prior invasive cancer (except nonmelanoma skin cancer) unless disease free for at least 2 years or life expectancy without treatment is greater than 2 years, e.g., low risk localized prostate cancer.

• - TREATMENT ELIGIBILITY CRITERIA: The subject has uncontrolled, significant intercurrent or recent illness including, but not limited to, the following conditions: - Cardiovascular disorders: - Congestive heart failure New York Heart Association class 3 or 4, unstable angina pectoris, serious cardiac arrhythmias.

• - Uncontrolled hypertension defined as sustained blood pressure (BP) > 150 mm Hg systolic or > 100 mm Hg diastolic despite optimal antihypertensive treatment.

• - Stroke (including transient ischemic attack [TIA]), myocardial infarction (MI), or other ischemic event, or thromboembolic event (e.g., deep venous thrombosis, pulmonary embolism) within 6 months of screening.

Patients receiving anti-coagulant therapy for previous thromboembolic event will be allowed to enroll on study.

• - Other clinically significant disorders that would preclude safe study participation.

• - End stage Renal disease.

• - Advanced liver disease such as cirrhosis, chronic active hepatitis or chronic persistent hepatitis.

• - Active (acute or chronic) or uncontrolled severe infection.

• - TREATMENT ELIGIBILITY CRITERIA: Known history of HIV, chronic hepatitis B virus (HBV), or hepatitis C virus (HCV) infection.

PRIMARY OBJECTIVES:

• I. To understand effects of continuous positive airway pressure (CPAP) for obstructive sleep apnea (OSA) on the course of polycythemia vera/essential thrombocythemia (PV/ET).

EXPLORATORY OBJECTIVES:

• I. To estimate prevalence of OSA in patients with myeloproliferative neoplasms.

• II. To understand effects of CPAP for sleep apnea on the course of myeloproliferative neoplasms (MPNs).

• III. To correlate OSA severity with thrombotic and inflammatory marker values in patients with PV/ET at baseline.

OUTLINE: Patients are assigned to 1 of 2 cohorts. COHORT I (OBSERVATIONAL COHORT): Patients not diagnosed with OSA undergo observation for 6 months. COHORT II (TREATMENT COHORT): Patients diagnosed with OSA and prescribed a CPAP machine for treatment receive continuous treatment with CPAP for 6 months.

Arms

Active Comparator: Cohort I (observation)

Patients not diagnosed with OSA undergo observation for 6 months.

Experimental: Cohort II: (CPAP treatment)

Patients diagnosed with OSA and prescribed a CPAP machine for treatment receive continuous treatment with CPAP for 6 months.

Interventions

Procedure: - Continuous Positive Airway Pressure

Receive CPAP treatment

Other: - Patient Observation

Undergo observation

Other: - Questionnaire Administration

Ancillary studies