Pacritinib to Inhibit JAK/STAT Signaling in Refractory Colorectal Cancer

Inclusion Criteria: * Histologically or cytologically confirmed refractory colorectal cancer * Measurable disease defined as lesions that can be accurately measured in at least one dimension (longest diameter to be recorded) as \>10 mm with CT scan, as \>20 mm by chest x-ray, or \>10 mm with calipers by clinical exam. * Refractory to or intolerant of standard systemic therapy, including having received two or more standard available therapies known to prolong survival for which s/he was eligible, including FOLFOX or FOLFIRI with or without bevacizumab, aflibercept, cetuximab, or panitumumab * At least 18 years of age. * ECOG performance status \< 2 * Life expectancy ≥ 12 weeks. * Normal bone marrow and organ function as defined below: * Absolute neutrophil count ≥ 1,500/mcl * Platelets ≥ 50,000/mcl * Total bilirubin ≤ 2.0 x IULN * AST (SGOT) / ALT (SGPT) ≤ 3.0 x IULN * Serum creatinine ≤ 2.0 mg/dL OR creatinine clearance \> 60 mL/min/1.73 m2 for patients with creatinine levels above 2.0 mg/dL * Women of childbearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control, abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while participating in this study, she must inform her treating physician immediately. * Able to understand and willing to sign an IRB approved written informed consent document (or that of legally authorized representative, if applicable). Exclusion Criteria: * Prior therapy with a JAK2 or FLT3 inhibitor. * A history of other malignancy ≤ 5 years previous with the exception of basal cell or squamous cell carcinoma of the skin which were treated with local resection only or carcinoma in situ of the cervix. * Received any chemotherapeutic or targeted agent for metastatic colorectal cancer within two weeks of initiation of study drug. * Currently receiving any other investigational agents. * Known brain metastases. Patients with known brain metastases must be excluded from this clinical trial because of their poor prognosis and because they often develop progressive neurologic dysfunction that would confound the evaluation of neurologic and other adverse events. * A history of allergic reactions attributed to compounds of similar chemical or biologic composition to pacritinib or other agents used in the study. * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. * Pregnant and/or breastfeeding. Patient must have a negative pregnancy test within 14 days of study entry. * Known HIV-positivity on combination antiretroviral therapy because of the potential for pharmacokinetic interactions with pacritinib. In addition, these patients are at increased risk of lethal infections when treated with marrow-suppressive therapy. Appropriate studies will be undertaken in patients receiving combination antiretroviral therapy when indicated. * Use of potent cytochrome P450 3A4 (CYP3A4) inhibitor within one week of pacritinib initiation. * Patients with CTCAE grade 2 cardiac arrhythmias may be considered for inclusion if the arrhythmias are stable, asymptomatic, and unlikely to affect patient safety. Patients will be excluded if they have ongoing cardiac dysrhythmias of CTCAE grade ≥ 3, corrected QT interval (QTc) prolongation \>450ms, or other factors that increase the risk for QT interval prolongation (eg, heart failure, hypokalemia \[defined as serum potassium \<3.0mEq/L that is persistent and refractory to correction\], or family history of long QT interval syndrome). * Any gastrointestinal (GI) or metabolic condition that could interfere with absorption of oral medication such as ongoing grade 3 or higher diarrhea, constipation, nausea, or vomiting. * Active viral hepatitis.