A Phase 1 Study of XL019 in Adults With Polycythemia Vera

Inclusion Criteria: * The subject has a diagnosis of polycythemia vera (PV), and has failed, or is intolerant of, standard therapies or refuses to take standard medications. * The subject is ≥18 years old. * The subject has an Eastern Cooperative Oncology Group (ECOG) performance status of ≤2. * The subject has adequate organ function. * Subjects who have received phlebotomy due to PV must have documented phlebotomy history for 12 weeks prior to enrollment. * The subject has the capability of understanding the informed consent document and has signed the informed consent document. * Sexually active subjects (male and female) must use medically acceptable methods of contraception during the course of the study. * Female subjects of childbearing potential must have a negative pregnancy test at screening. * The subject has had no other diagnosis of malignancy or evidence of other malignancey for 2 years prior to screening for this study (except non-melanoma skin cancer or in situ carcinoma of the cervix). Exclusion Criteria: * The subject has received treatment for PV within 14 days prior to first dose of XL019 * The subject has uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, hypertension, symptomatic congestive heart failure, unstable angina pectoris, myocardial infarction within 3 months, or cardiac arrhythmias. * The subject is pregnant or breastfeeding. * The subject is known to be positive for the human immunodeficiency virus (HIV). * The subject is unable or unwilling to abide by the study protocol or cooperate fully with the investigator or designee.