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JK

Johannes Jacob Pieter Kastelein

NAMS
CHIEF SCIENTIFIC OFFICER · NEWAMSTERDAM PHARMA CO N.V. · CIK 0002000389
FILING MIX · LIFETIME43%/57%
BUYS
13
SELLS
17
TOTAL VALUE
$17.72M
COMPANIES
1
ACTIVE SINCE
Jan 2024
HOLDINGS NOW
170,711
AVG SELL PX
$27.13
TRADE KIND
SHOWING 30 / 30
Trades · vs SPY
Loading price series…
Performance · forward returns vs SPY
10 backtested trades · 8 horizons · 23 pending
Forward-return performance of every backtestable P/S trade by Johannes Jacob Pieter Kastelein, measured at 8 horizons from 7 days to 2 years. Deduped per economic event so co-filings count once. Excess return = trade return minus SPY return over the same window.
HORIZONTRADESWIN RATEINSIDER RETURNSPY RETURNMEAN EXCESSMEDIAN EXCESST-STAT
7d10+100.00%-2.69%-0.30%-2.39%-3.05%—
14d10+60.00%-3.54%-1.37%-2.18%+0.68%—
30d10+40.00%+2.14%-0.80%+2.94%+4.82%—
60d10+60.00%+12.54%+3.95%+8.59%-7.00%—
90d10+30.00%+15.56%+2.66%+22.41%+27.91%—
180d10(5 pending)+20.00%+20.48%+7.79%+12.69%+36.69%—
1y10(9 pending)+100.00%-0.70%+10.99%-11.69%-11.69%—
2y10(9 pending)+0.00%+37.54%+25.92%+11.62%+11.62%—
How to read this: Insider Returnis the average raw return of the filer's trades over the horizon. SPY Return is what SPY did over those same windows — reference only, not a comparison. The headline alpha number is Mean Excess = Insider − SPY; green means the filer beat SPY, red means they trailed it. Win rate is the share of individual trades where the filer beat SPY. T-statvalues above 2 mean the alpha is unlikely to be chance given the sample size. "Pending" counts trades where the horizon hasn't elapsed yet; their stats are not included in the row average.
Holdings over time
NAMS · 170,711 shares · as of Mar 9, 2026
0242,557485,115727,672970,229202420252026SHARES HELD
Trading cadence · quarterly flow
BUY ● SELL ●
2024
2024
2024
2024
2025
2025
2025
2025
2026
FLOW · 13 buys / 17 sellsCOVERAGE · 9 quarters
Form 4 filings · all activity
COMPANYTYPESHARESPRICEVALUEHELD AFTERTRADE DATEFILEDDETAILS
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE10b5-1
10b5-1 plan
101,409$30.29$3.07M69,302Mar 9, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
101,409——520,229Mar 9, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASE
Chief Scientific Officer
101,409——170,711Mar 9, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE10b5-1
10b5-1 plan
94,124$30.32$2.85M69,302Mar 6, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
94,124——621,638Mar 6, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASE
Chief Scientific Officer
94,124——163,426Mar 6, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASE
Chief Scientific Officer
104,467——173,769Mar 5, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
104,467——715,762Mar 5, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE10b5-1
10b5-1 plan
104,467$30.30$3.17M69,302Mar 5, 2026Mar 9, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
30,789$35.46$1.09M53,500Feb 20, 2026Feb 24, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
14,692$35.00$514.2K84,289Feb 20, 2026Feb 24, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASEGRANT
Stock grant
115,000——115,000Jan 7, 2026Jan 7, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASEGRANT
Stock grant
25,500——98,981Jan 7, 2026Jan 7, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE10b5-1
10b5-1 plan
6,000$33.25$199.5K73,481Jan 5, 2026Jan 7, 2026 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
42,342$25.08$1.06M76,960Aug 22, 2025Aug 25, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
7,658$25.49$195.2K69,302Aug 22, 2025Aug 25, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
50,000$24.29$1.21M119,302Aug 21, 2025Aug 25, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
45,481——0Mar 26, 2025Mar 28, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASE
Chief Scientific Officer
45,481——79,481Mar 26, 2025Mar 28, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASEGRANT
Stock grant
19,302——169,302Mar 26, 2025Mar 28, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASEGRANT
Stock grant
45,481——45,481Mar 26, 2025Mar 28, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASE
Chief Scientific Officer
150,000——150,000Mar 24, 2025Mar 26, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
150,000——820,229Mar 24, 2025Mar 26, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASEGRANT
Stock grant
34,000——34,000Jan 7, 2025Jan 7, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASEGRANT
Stock grant
200,000——200,000Jan 2, 2025Jan 6, 2025 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
11,197$22.72$254.4K190,476Mar 26, 2024Mar 27, 2024 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
201,673——970,229Mar 26, 2024Mar 27, 2024 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
SALE
Chief Scientific Officer
190,476$21.50$4.10M0Mar 26, 2024Mar 27, 2024 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASE
Chief Scientific Officer
201,673——201,673Mar 26, 2024Mar 27, 2024 ↗View →
NAMS
NEWAMSTERDAM PHARMA CO N.V.
PURCHASEGRANT
Stock grant
500,000——500,000Jan 1, 2024Jan 3, 2024 ↗View →
Other insiders · NAMS
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About this filer
CIK 0002000389
ROLE
Chief Scientific Officer
PRIMARY
NAMS
COMPANIES
1
ACTIVE SINCE
Jan 2024
MARKETPEEL · /INSIDER/0002000389DATA · SEC EDGAR · FORM 4 · CONSOLIDATED TAPE
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