Initial qualitative interviews were conducted with 19 oncologists, hematologists, and hematologist-oncologists to help inform the development of the chart review survey. A specific focus of these interviews was to understand how clinicians manage patients with PV and clinicians’ experiences with HU therapy. These consisted of 1-h individual in-person detailed interviews conducted by a trained moderator using a structured discussion guide.
Physicians were recruited for this study between April and July 2014 to complete an online collation of data gathered from a retrospective chart review. Recruitment was conducted via email from a nationally-representative online panel of board-certified hematologists, oncologists, and hematologist-oncologists who had agreed to participate in blinded periodic research surveys. The recruitment of panel members was not solely based on convenience, as an attempt was made to match the characteristics of the broader population of the American Medical Association specialized in the treatment of cancer or blood disorders (see Additional file 1: Table S1). Physicians were eligible if they spent ≥50 % of their time on direct patient care and had ≥5 patients with PV under their care in the past 12 months, at least 25 % of whom had current or prior HU exposure. Physicians were compensated for their participation.
Participating physicians selected 4 charts for patients meeting the following criteria: age ≥18 years, alive at or deceased within the past 6 months from the time of chart abstraction, previously diagnosed with PV per physician judgement, with a disease duration of 3–15 years, having received HU therapy for ≥2 months within the last 5 years, having medical record data 12 months both before and after HU initiation, and having not been part of a PV-related clinical trial.
Chart review survey
Physicians entered all of their responses into an online data collection tool. This retrospective chart review first consisted of questions—completed by each physician in approximately 5 min—on general features of their clinical management of PV, along with demographic (e.g., age, sex) and practice information (e.g., specialty, years in practice, population density of catchment area, etc.).
Physicians then addressed questions regarding each patient. This information included patient demographics (e.g., age, sex, race/ethnicity, employment status, and insurance) and general health history information, such as body mass index and comorbidities.
PV-specific questions included the number of years since initial diagnosis and the various signs/symptoms (e.g., splenomegaly, fatigue), clinical events (e.g., stroke), qualitative laboratory anomalies (e.g., anemia, blast elevation), and discrete/measured laboratory test parameters (i.e., Hct, WBC counts, and platelet counts) that were present at 3 time-points for each patient: initial diagnosis, following the initiation of HU treatment, and during the past 12 months.
Physicians also answered several questions regarding HU treatment, including whether patients were still on HU or had discontinued HU (and how long ago), along with the highest, lowest, and most stable (the latter left up to the interpretation of the physician) doses of HU, if this information was available/retrievable. For patients still using HU, their current dose was reported, whereas for patients who had discontinued HU, their dose just prior to discontinuation was collected.
A CHR variable was determined for each patient. The CHR variable was modeled after the ELN definition  but was limited by the nature of the data collected in this study (e.g., absence of documentation of the duration of spleen/symptom resolution, absence of or poor documentation of the presence of hemorrhagic or thrombotic events over the follow-up period, and no availability of bone marrow serial specimens necessary to document histologic remission). Specifically, a CR in this analysis was defined as the combination of all the following target criteria being met: Hct <45 %, platelet count ≤400 × 109/L, WBC count ≤10 × 109/L, achievement of a normal spleen size (i.e., lack of an enlarged spleen as reported by the physician), and absence of disease-related symptoms (i.e., pruritus, fatigue, or headache). Patients who did not meet all of the criteria for a CR but had Hct <45 % without concomitant PBT or had a response in 3 or 4 of the 5 CR criteria previously mentioned were considered to have a PR. All others were considered to have no response.
Physician and patient demographics and health history were reported descriptively using means and standard deviations for continuous variables and frequencies and percentages for categorical variables. Treatment history and disease symptoms were compared between those who discontinued and those who were currently treated with HU using Chi square tests and one-way analyses of variance for categorical and continuous variables, respectively. CHR and the achievement of individual blood count target thresholds were reported descriptively (frequencies and percentages).
Ethics, consent, and permissions
The study was conducted in compliance with the Declaration of Helsinki. All study materials were reviewed and approved by an independent institutional review board (Sterling IRB [Atlanta, GA, USA]; protocol number, 161101176).