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 Q4 2023?

104 institutional investors reported MRSN - Mersana Therapeutics, Inc. - Common Stock, par value $0.0001 per share for Q4 2023. Use the holders table for investor-level position and value details.

CUSIP: 59045L106

Q4 2023 13F Holders as of 31 Dec 2023

Security type / class: Equity / Common Stock, par value $0.0001 per share
Total 13F shares: 113,095,763
Total 13F value: $262,379,163
Share change: +248,919
Put/Call ratio: 3.1%
SEC-reported price per share: $2.32
Number of holders: 104
Value change: +$21,039,242
Number of buys: 49
Number of sells: 73
Shares outstanding: 4,992,318

Security key

59045L106

Report period

Q4 2023

Institutions

104

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

EcoR1 Capital, LLC

Disclosed value leader

EcoR1 Capital, LLC

Comparable rows

0/15

Latest evidence

30 Sep 2023

13F Highest disclosed value: $24,593,154 15 rows are not safely comparable across share classes. Showing 1-6 of 15 holder rows.

Quick read

EcoR1 Capital, LLC has the largest disclosed position value at $24.59M.

0 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 EcoR1 Capital, LLC's linked filing trail.

Disclosed position value Top 5

EcoR1 Capital, LLC $24.59M

Venrock Adviser, LLC $14.39M

Bain Capital Life Sciences Invest... $11M

BlackRock Finance, Inc. $10.13M

VANGUARD GROUP INC $7.86M

Value bars compare disclosed positions; verify each figure against the linked filing evidence.

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

Holder	Evidence	Ownership %	Position	12M Net Δ	As of
EcoR1 Capital, LLC	13F Company 13F	— denominator unverified	$24,593,154 19,364,688 shares	—	30 Sep 2023
Venrock Adviser, LLC	13F Company 13F	— denominator unverified	$14,386,560 11,328,000 shares	—	30 Sep 2023
Bain Capital Life Sciences Investors, LLC	13F Company 13F	— denominator unverified	$11,002,865 8,663,673 shares	—	30 Sep 2023
BlackRock Finance, Inc.	13F Company 13F	— denominator unverified	$10,125,278 7,972,660 shares	—	30 Sep 2023
VANGUARD GROUP INC	13F Company 13F	— denominator unverified	$7,856,376 6,186,123 shares	—	30 Sep 2023
Bellevue Group AG	13F Company 13F	— denominator unverified	$6,627,654 5,218,625 shares	—	30 Sep 2023

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 Q4 2023

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

Institutions

104

113,095,763

Rows available

104

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 Q4 2023 vs Q4 2025 Across Filers

Q4 2025 holders

Q4 2023 holders

104

Holder diff

101

Investor	Q4 2025 Shares	Q4 2023 Shares	Share Diff	Share Chg %	Q4 2025 value	Q4 2023 value	Value change	Value Chg %

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

Quarterly Holders Trend

Quarterly Value Trend

Quarterly Shares Trend