Castor
Castor builds software to run clinical trials, with modules for patient recruitment, data collection and analysis. The 309-person company has raised $64M, including a Series B in 2021 backed by healthcare-focused investors like F-Prime and Eight Roads.
The growth story
Castor grew from 221 to 309 employees between 2021 and 2026, raising $64M along the way, most recently a Series B in July 2021.
About
Castor sells a modular platform that helps pharmaceutical and research organizations design and manage clinical trials. Its tools handle patient enrollment, monitoring, and data analysis, aiming to make trials more accessible globally.
The company last raised $64M in a 2021 Series B with investors specializing in healthcare tech. While headcount growth data is unavailable, its engineering team makes up the largest function at 24 people.
Founders and leadership
Engineering is the largest department with 24 staff. The company has a median tenure of 2 years, suggesting moderate turnover compared to typical tech startups.
The Castor org chart
Derk Arts, MD PhD (Founder & CEO) leads 41 mapped leaders with 7 direct reports. Click +N to expand a team; names link to the person’s public profile.
Departments, and which ones grew
Headcount by function: Operations 73 (+24% YoY), Engineering 37 (+3% YoY), Sales 24 (+14% YoY), Business Development 19 (+6% YoY), Information Technology 16 (+33% YoY), Entrepreneurship 14 (-12% YoY).
Talent flow
Castor recruits heavily from clinical research organizations like Science 37 and EPAM. Alumni frequently move to healthcare tech firms such as Medrio and REDCap Cloud, though some join unrelated companies like Tesla.
Most common previous employers of Castor staff: Science 37 (3), EPAM (3), Amsterdam UMC (2), ERT (2), PPD (2), Ksyos (2). Former Castor employees most often moved to Choco (5), Medrio (3), Scilife (3), Tesla (2), REDCap Cloud (2), Coolset (2).
Alumni worth knowing
The Castor mafia
11 alumni have founded companies, including Bioretec (59 staff) and Coolset (18 staff). These span healthcare tech and climate tech, showing diverse entrepreneurial outcomes.
11Sarah van Hellenberg Hubar-Fisher, was Member of the Board of Advisors until 2023David Sigley, was Head Of Engineering until 2022Olivier Magnin, was Sr. Strategy Manager until 2022Dr. Amir Lahav, was Scientific Advisory Board Member until 2023Zhenya Bankouski, was Head of Revenue Operations and BI until 2022Andreas Ingvar Õismaa, was Researcher - Interoperability Architecture in Clinical Research until 2022
Wasim Shaikh, PMP®, was Senior Project Manager until 2024
Martin Ericsson, was Investor until 2026
KHALED ABULJEBAIN, was Business Development until 2020
Zena Horaibi, was Business Development Executive until 2022
Aleksei Lazarev, was Senior Frontend Developer until 2018Hiring now
Web traffic
Traffic mix: 62% direct, 18% search, 6% social, 0% paid.
What this company is made of
Most common skills at Castor: Project Management (34), Microsoft Office (32), SQL (32), Communication (30), Leadership (28), English (28), Management (27), Customer Service (27).
Where the team actually sits
Castor people are concentrated in North Holland, Netherlands (15), Netherlands (11), England, United Kingdom (7), North Carolina, United States (3).
Search footprint
Castor attracts about 1,111 organic search visits a month, traffic worth roughly $16K a month if bought through ads. It gained 1,096 ranking keywords and lost 1,043 in the last period.
What employees say
- Compensation
- 4.00 / 5
- Career opportunities
- 3.60 / 5
- Senior management
- 3.70 / 5
- Work-life balance
- 4.30 / 5
Frequently asked
Castor has 309 employees as of September 2026.
Castor has raised $64M in total, most recently a Series B round in July 2021.
Castor was founded in 2011 by Derk Arts, MD PhD, Sebastiaan Knijnenburg, Rob de Vries.
Derk Arts, MD PhD (Founder & CEO) sits at the top of Castor's reporting structure, with 7 direct reports.
The most common previous employers of current Castor staff are Science 37 (3 people), EPAM (3 people), Amsterdam UMC (2 people).
Former Castor employees most often move to Choco (5), Medrio (3), Scilife (3).
At least 11 companies have a founder who previously worked at Castor, including Bioretec, Coolset, EvidenceHunt.
Castor attracts about 1,111 organic search visits a month, worth roughly $16K a month in equivalent ad spend.
The most common skills among Castor staff are Project Management, Microsoft Office, SQL, Communication, Leadership.
Castor staff are concentrated in North Holland, Netherlands (15), Netherlands (11), England, United Kingdom (7).
Castor has about 73 people in Operations, up 24% over the past year, as of September 2026.
Castor has about 37 people in Engineering, up 3% over the past year, as of September 2026.
Computed from 86 current and 263 former Castor profiles, as of September 2026. Source: Crustdata.
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