The purpose of this study is to understand why there is a greater risk of thrombosis in patients who have the JAK2 mutation as compared to those with CALR mutations.

This biospecimen study is designed to evaluate the expression levels of TLR 2 and TLR 4 on mononuclear cells in CALR mutation positive MPN participants and compare to JAK2 V617F mutation positive MPN patients and healthy controls. Patients who have MPN with the CALR mutation positive will be approached for interest in participating in this study. A research blood collection will occur at any time during the participant's cancer trajectory after enrollment, during a standard of care blood draw. The participant's demographics, MPN subtype, CALR mutation status, history of thrombosis/other medical history, and current, concomitant medications will be collected once. Clinical data will be collected, including results from the CBC with differential, complete metabolic panel (if available), and PT/PTT/INR (if available) drawn closest to the research blood collection. This study will initially open as a single center study at AHWFBCCC.

Inclusion Criteria:

• Written (or electronic) informed consent and HIPAA authorization for release of personal health information by participant or his/her legally authorized representative (LAR).
• Age ≥ 18 years at the time of enrollment
• Diagnosis of myeloproliferative neoplasm (MPN) according to 2022 World Health Organization classification of MDS/MPNs
• CALR-positive genetic mutation

Exclusion Criteria:

- Diagnosis of MPN with JAK2 V617F mutation

Patients seen in the clinic with MPN with the CALR mutation will be identified and approached for consent.

Releasing the Individual Participant Data (IPD) is not required to meet the study objectives, and therefore is not planned to be released. Additionally, there is no plan to share data, particularly individual participant data, with anyone who is not already involved in the study