Mersana Therapeutics, Inc. - Common Stock, par value $0.0001 per share (MRSN)

Q: What does CUSIP 59045L106 represent in this 13F holders report?

CUSIP 59045L106 is the security identifier for MRSN - Mersana Therapeutics, Inc. - Common Stock, par value $0.0001 per share used to aggregate holder disclosures.

Q: How many institutions held MRSN - Mersana Therapeutics, Inc. - Common Stock, par value $0.0001 per share in Q1 2025?

109 institutional investors reported MRSN - Mersana Therapeutics, Inc. - Common Stock, par value $0.0001 per share for Q1 2025. Use the holders table for investor-level position and value details.

CUSIP: 59045L106

Q1 2025 13F Holders as of 31 Mar 2025

Security type / class: Equity / Common Stock, par value $0.0001 per share
Total 13F shares: 87,949,584
Total 13F value: $30,264,885
Share change: -16,798,108
Put/Call ratio: 80%
SEC-reported price per share: $0.34
Number of holders: 109
Value change: -$35,777,339
Number of buys: 51
Number of sells: 80
Shares outstanding: 4,992,318

Security key

59045L106

Report period

Q1 2025

Institutions

109

Top holders

MRSN full security history Ownership snapshot Full 13F holder table Newer quarter: Q4 2025 Mersana Therapeutics, Inc. SEC filings Mersana Therapeutics, Inc. company facts

Broader feeds

Latest 13F filings Latest 13D/G filings Investors directory

Reporting periods

Holder history for CUSIP 59045L106

Newer quarter: Q4 2025

Recent filing periods:

Q1 2026 Q4 2025

Ownership snapshot

Top reported holders of MRSN - Mersana Therapeutics, Inc. - Common Stock, par value $0.0001 per share (13F + 13D/G + 3/4/5)

Grouped by holder across the latest SEC ownership disclosures. Start with comparable ownership when available, then verify the linked 13F, 13D/G, or 3/4/5 evidence.

Comparable stake leader

Nextech Crossover I GP S....

Disclosed value leader

EcoR1 Capital, LLC

Comparable rows

15/15

Latest evidence

31 Mar 2025

13D/G 13F 3/4/5 Lead comparable stake: 10% 13D/G row: Nextech Crossover I GP S.a r.l. Showing 1-6 of 15 holder rows.

Quick read

Nextech Crossover I GP S.a r.l. leads the comparable SEC ownership view at 10%.

15 of 15 rows have a safely comparable ownership percentage. Use this as a filing-backed starting point, then open the detailed table for source links, reporting role, position value, share count, and filing date.

Open SEC evidence Opens Nextech Crossover I GP S.a r.l.'s linked filing trail.

Comparable ownership Top 5

Nextech Crossover I GP S.a r.l. 10%

VANGUARD GROUP INC 6.7%

Venrock Healthcare Capital Partne... 2.9%

Nextech Invest Ltd. 242%

EcoR1 Capital, LLC 227%

Ownership % is shown only when SEC disclosures are safely comparable across share classes.

Detailed SEC evidence table Showing 1-6 of 15 holder rows

Holder	Evidence	Ownership %	Position	12M Net Δ	As of
Nextech Crossover I GP S.a r.l.	13D/G 13D/G	10%	$4,344,209 12,067,246 shares	$0	20 Dec 2024
VANGUARD GROUP INC	13F 13D/G Company · The Vanguard Group 13F 13D/G	6.7% from 13D/G	$10,092,247 7,057,516 shares	—	31 Dec 2024
Venrock Healthcare Capital Partners III, L.P.	13D/G 13D/G	2.9%	$1,286,757 3,574,325 shares	-$2,406,047	31 Mar 2025
Nextech Invest Ltd.	13F Company 13F	242%	$17,256,162 12,067,246 shares	—	31 Dec 2024
EcoR1 Capital, LLC	3/4/5 13F 10%+ Owner · Company 3/4/5 13F	227% from 13F	$21,523,200 19,364,688 shares mixed-class rows	—	19 Dec 2024
Venrock Adviser, LLC	13F Company 13F	205%	$14,668,640 10,257,790 shares	—	31 Dec 2024

How to read this table

Rows are grouped by holder and ranked first by SEC-reported ownership % when it is safely comparable, then by disclosed holdings value. — indicates unavailable or non-comparable values; "mixed-class rows" means the latest filing spans non-comparable classes.

13F holder rows

Institutional holders as of Q1 2025

Investor-level positions for this CUSIP, loaded as an interactive table.

Institutions

109

87,949,584

Rows available

109

Investor	Option	Weight %	Change %	SEC-reported value	* Price	Shares	Share Change	Activity	Report Period

^* SEC-reported price is the security price as of the portfolio date and can indicate the last known price at which the security was still held. The marker flags a reported price that did not pass the local price check.

Compare Q1 2025 vs Q4 2025 Across Filers

Q4 2025 holders

Q1 2025 holders

109

Holder diff

106

Investor	Q4 2025 Shares	Q1 2025 Shares	Share Diff	Share Chg %	Q4 2025 value	Q1 2025 value	Value change	Value Chg %

Trend: ostatnie 8 kwartałów (+ wybrane okresy porównania).

Quarterly Holders Trend

Quarterly Value Trend

Quarterly Shares Trend