PRTA · PROTHENA CORP PUBLIC LTD CO

Prothena Corporation plc, a late-stage clinical biotechnology company, focuses on discovery and development of novel therapies to treat diseases caused by protein dysregulation. Its product pipeline includes Prasinezumab, an investigational humanized monoclonal antibody which is in Phase 3 clinical trial for the treatment of parkinson's disease and other synucleinopathies. The company also develops Coramitug, an investigational antibody, which is in Phase 3 clinical trial for the treatment of transthyretin amyloidosis; BMS-986446, an anti-tau antibody which is in Phase 2 clinical trial to treat Alzheimer's disease; PRX019, an investigational antibody which is in Phase 1 clinical trial for the treatment of neurodegenerative diseases; and PRX123, a Dual Aß-Tau Vaccine, which is in preclinical trial for treating Alzheimer's disease. In addition, it develops discovery- and late-preclinical-stage programs include TDP-43 CYTOPE for the treatment of amyotrophic lateral sclerosis; PRX012, a next-generation anti-Aß antibody which is in phase 1 clinical trial to treat Alzheimer's disease; and PRX012-TfR, a preclinical program for the treatment of Alzheimer's disease. It has a license, development, and commercialization agreement with F. Hoffmann-La Roche Ltd. and Hoffmann-La Roche Inc. to develop and commercialize antibodies that target a-synuclein, including prasinezumab; and master collaboration agreement with Bristol Myers Squibb to develop and commercialize antibodies targeting tau, TDP-43. Prothena Corporation plc was incorporated in 2012 and is based in Dublin, Ireland.

Cap structure and valuation

Cap structure
SP	$8.45
SO	51.3M
Options	11.8M
Warrants	0.0M
FD SO	63.1M
MC	$533.2M

Cash	$288.2M
Total debt	—
EV	$245.0M

TTM Multiples
EV / Revenue	4.5x
EV / EBITDA	—
MC / Net Income	—
EV / FCF	—
MC / FCF	—

Ownership & coverage
Institutional	93.3%
Insiders	22.3%
# Institutions	255
Analysts	5
Consensus	—
Avg target	$21.40

Short % float	18.8%
Days to cover	17.58

MC = SP × FD SO. EV = MC + Debt − Cash. SP = previous yfinance close. Balance-sheet figures as of 2026-07-30. Multiples use TTM (sum of last 4 quarters); shown as "—" when the denominator is zero or negative, or when fewer than four quarters are reported — a partial sum is not a trailing twelve months. Ownership & coverage per Yahoo Finance as of 2026-10-12 — institutional % is 13F-based, so it can lag a quarter and exceed 100% on share-count timing. Short interest per FINRA bi-monthly reporting, as of 2026-09-30; the float denominator can be unreliable on tiny floats.

Financial statements

	6/30/26	3/31/26	12/31/25	9/30/25
Total Revenue	1.01	51.08	0.02	2.42
Revenue YoY %	(77.1%)	1706.4%	(99.0%)	149.0%
Gross Profit	—	42.70	—	—
Gross Margin %	—	83.6%	—	—

SG&A	10.90	12.67	12.65	13.24
R&D	8.80	12.63	14.59	28.94

Operating Income	(21.10)	30.04	(24.20)	(40.24)
Operating Income YoY %	75.1%	145.8%	62.7%	39.5%
Operating Margin %	(2089.2%)	58.8%	(115252.4%)	(1666.3%)
EBITDA	(20.90)	30.22	(23.98)	(40.01)
EBITDA Margin %	(2069.7%)	59.2%	(114214.3%)	(1656.8%)

Interest Expense	2.55	2.42	2.65	3.35
Other Income / (Expense)	5.07	5.10	5.27	6.68
Pretax Income	(18.58)	32.72	(21.58)	(36.91)
Tax Provision	0.00	0.00	0.01	(0.37)
Net Income	(18.58)	32.72	(21.59)	(36.54)
Net Margin %	(1839.9%)	64.1%	(102804.8%)	(1513.1%)

Diluted EPS	-$0.36	$0.60	-$0.40	-$0.68
Basic EPS	-$0.36	$0.61	-$0.40	-$0.68
Diluted Avg Shares	52.1	54.1	—	53.8
Basic Avg Shares	52.1	53.7	—	53.8

	LTM	12/31/25	12/31/24	12/31/23	12/31/22
Total Revenue	54.53	9.68	135.16	91.37	53.91
Revenue YoY %	463.1%	(92.8%)	47.9%	69.5%	—

SG&A	49.45	59.39	67.20	61.84	49.90
R&D	64.95	134.85	222.52	220.57	135.56

Operating Income	(55.51)	(214.64)	(154.56)	(191.04)	(131.56)
Operating Income YoY %	74.1%	(38.9%)	19.1%	(45.2%)	—
Operating Margin %	(101.8%)	(2216.4%)	(114.4%)	(209.1%)	(244.1%)
EBITDA	(54.68)	(213.75)	(153.67)	(190.11)	(130.81)
EBITDA Margin %	(100.3%)	(2207.2%)	(113.7%)	(208.1%)	(242.7%)

Interest Expense	10.97	14.14	25.82	31.01	6.35
Other Income / (Expense)	22.12	27.95	51.45	61.57	12.30
Pretax Income	(44.35)	(200.83)	(128.93)	(160.48)	(125.61)
Tax Provision	(0.36)	43.26	(6.62)	(13.45)	(8.66)
Net Income	(43.99)	(244.09)	(122.31)	(147.03)	(116.95)
Net Margin %	(80.7%)	(2520.6%)	(90.5%)	(160.9%)	(217.0%)

Diluted EPS	-$0.84	-$4.53	-$2.27	-$2.76	-$2.47
Basic EPS	-$0.83	-$4.53	-$2.27	-$2.76	-$2.47
Diluted Avg Shares	52.1	53.8	53.8	53.2	47.4
Basic Avg Shares	52.1	53.8	53.8	53.2	47.4

	6/30/26	3/31/26	12/31/25	9/30/25
Cash & Equivalents	288.19	329.46	307.53	330.84
Other Current Assets	3.82	9.74	7.66	9.13
Total Current Assets	292.01	339.20	315.19	339.97

Net PPE	2.49	1.96	2.14	2.46
Operating Lease ROU	6.74	7.39	8.12	8.85
Total Assets	302.58	349.89	326.80	352.63

Accounts Payable	1.94	4.30	5.88	10.50
Current Lease Liabilities	2.96	2.89	2.89	2.88
Other Current Liabilities	6.76	25.32	32.08	38.05
Total Current Liabilities	11.66	32.52	40.84	51.44
Long-term Lease Liabilities	4.03	4.76	5.49	6.20
Total Liabilities	15.69	37.28	46.33	57.64

Retained Earnings	(1,332.30)	(1,313.71)	(1,346.43)	(1,324.84)
Total Equity	286.89	312.62	280.47	294.99

	LTM	12/31/25	12/31/24	12/31/23	12/31/22
Cash & Equivalents	288.19	307.53	471.39	618.83	710.41
Receivables	—	—	0.00	5.16	0.00
Other Current Assets	3.82	7.66	14.02	15.29	8.69
Total Current Assets	292.01	315.19	485.41	639.28	719.10

Net PPE	2.49	2.14	3.08	3.84	1.73
Operating Lease ROU	6.74	8.12	10.71	12.16	6.28
Other Assets	—	—	47.91	41.10	30.93
Total Assets	302.58	326.80	547.11	696.38	758.03

Accounts Payable	1.94	5.88	7.77	25.39	9.27
Current Lease Liabilities	2.96	2.89	2.61	1.11	6.47
Other Current Liabilities	6.76	32.08	38.12	30.39	34.40
Total Current Liabilities	11.66	40.84	48.50	56.89	50.15
Long-term Lease Liabilities	4.03	5.49	8.23	10.72	0.00
Other Liabilities	—	—	3.45	67.41	85.85
Total Liabilities	15.69	46.33	60.18	135.02	135.99

Retained Earnings	(1,332.30)	(1,346.43)	(1,102.34)	(980.03)	(833.00)
Total Equity	286.89	280.47	486.93	561.37	622.04

	6/30/26	3/31/26	12/31/25	9/30/25
Net Income	(18.58)	32.72	(21.59)	(36.54)
D&A	0.20	0.18	0.22	0.23
Stock-Based Comp	7.88	6.92	7.07	7.20
Δ Working Cap & Other	(14.54)	(10.94)	(9.02)	(11.45)
Operating Cash Flow	(25.05)	28.88	(23.31)	(40.56)

Other Investing	(0.65)	—	—	—
Investing Cash Flow	(0.65)	0.00	0.00	(0.01)

Other Financing	(15.57)	(6.95)	—	—
Financing Cash Flow	(15.57)	(6.95)	0.00	(0.02)

	LTM	12/31/25	12/31/24	12/31/23	12/31/22
Net Income	(43.99)	(244.09)	(122.31)	(147.03)	(116.95)
D&A	0.83	0.90	0.89	0.93	0.74
Stock-Based Comp	29.07	37.64	45.96	40.91	31.32
Δ Working Cap & Other	(45.95)	41.98	(74.60)	(28.72)	(23.94)
Operating Cash Flow	(60.05)	(163.58)	(150.05)	(133.91)	(108.82)

Other Investing	(0.66)	—	—	(2.77)	—
Investing Cash Flow	(0.66)	(0.14)	(0.30)	(2.77)	(0.46)

Other Financing	(22.53)	—	1.55	45.10	241.46
Financing Cash Flow	(22.53)	(0.14)	1.55	45.10	241.46

	6/30/26	3/31/26	12/31/25	9/30/25
Current Ratio	25.05	10.43	7.72	6.61
Quick Ratio	—	—	—	—
Debt / Equity	—	—	—	—
EBITDA Margin %	(2069.7%)	59.2%	(114214.3%)	(1656.8%)
Working Capital	280.36	306.68	274.35	288.54
Net Debt	—	—	—	—
ROE %	(6.5%)	10.5%	(7.7%)	(12.4%)
ROA %	(6.1%)	9.4%	(6.6%)	(10.4%)

	LTM	12/31/25	12/31/24	12/31/23	12/31/22
Current Ratio	25.05	7.72	10.01	11.24	14.34
Quick Ratio	—	—	—	—	—
Debt / Equity	—	—	—	—	—
EBITDA Margin %	(100.3%)	(2207.2%)	(113.7%)	(208.1%)	(242.7%)
Working Capital	280.36	274.35	436.91	582.39	668.95
Net Debt	—	—	—	—	—
ROE %	(15.3%)	(87.0%)	(25.1%)	(26.2%)	(18.8%)
ROA %	(14.5%)	(74.7%)	(22.4%)	(21.1%)	(15.4%)

Insider activity (last 2 years)

Date Filed	Reporter	Relationship	Trans. Date	Code	Shares	Price	Total Value
2026-10-09	SCULLY WILLIAM P	10% Owner	2026-10-08	P	90,000	$8.57	$770,904
2026-10-09	SCULLY WILLIAM P	10% Owner	2026-10-07	P	125,000	$8.40	$1,050,150
2026-10-06	SCULLY WILLIAM P	10% Owner	2026-10-02	P	100,000	$8.57	$857,240
2026-09-30	SCULLY WILLIAM P	10% Owner	2026-09-29	P	162,000	$8.68	$1,405,674
2026-09-29	SCULLY WILLIAM P	10% Owner	2026-09-28	P	103,500	$8.60	$889,872
2026-09-21	SCULLY WILLIAM P	10% Owner	2026-09-18	P	100,000	$8.43	$843,460
2026-09-03	SCULLY WILLIAM P	10% Owner	2026-09-02	P	27,000	$9.47	$255,739
2026-08-21	SCULLY WILLIAM P	10% Owner	2026-08-20	P	50,000	$8.79	$439,430
2026-08-18	SCULLY WILLIAM P	10% Owner	2026-08-18	G	(627,553)	—	$-0
2026-08-18	SCULLY WILLIAM P	10% Owner	2026-08-17	G	336,000	—	$0
2026-08-11	SCULLY WILLIAM P	10% Owner	2026-08-10	G	251,553	—	$0
2026-08-10	SCULLY WILLIAM P	10% Owner	2026-08-07	P	34,000	$8.62	$293,053
2026-08-10	SCULLY WILLIAM P	10% Owner	2026-08-07	P	3,500	$8.62	$30,167
2026-07-30	Kingston Anne Evans	Officer (Chief Strategy Officer)	2026-07-29	S	(7,662)	$8.47	-$64,919
2026-07-30	Isaacs Michael John	Officer (General Counsel & Company Sec.)	2026-07-29	S	(8,386)	$8.47	-$71,055
2026-07-30	Zago Wagner M.	Officer (Chief Scientific Officer)	2026-07-28	M	51,000	—	$0
2026-07-30	Zago Wagner M.	Officer (Chief Scientific Officer)	2026-07-28	D	(51,000)	$8.56	-$436,560
2026-07-30	Zago Wagner M.	Officer (Chief Scientific Officer)	2026-07-28	M	(51,000)	—	$-0
2026-07-30	Walker Karin L	Officer (Chief Accounting Officer)	2026-07-28	M	15,000	—	$0
2026-07-30	Walker Karin L	Officer (Chief Accounting Officer)	2026-07-28	D	(15,000)	$8.56	-$128,400
2026-07-30	Walker Karin L	Officer (Chief Accounting Officer)	2026-07-28	M	(15,000)	—	$-0
2026-07-30	Swanson Chad J.	Officer (Chief Development Officer)	2026-07-28	M	51,000	—	$0
2026-07-30	Swanson Chad J.	Officer (Chief Development Officer)	2026-07-28	D	(40,800)	$8.56	-$349,248
2026-07-30	Swanson Chad J.	Officer (Chief Development Officer)	2026-07-28	F	(3,467)	$8.56	-$29,678
2026-07-30	Swanson Chad J.	Officer (Chief Development Officer)	2026-07-28	M	(51,000)	—	$-0
2026-07-30	Smith Brandon S.	Officer (Chief Operating Officer)	2026-07-28	M	78,000	—	$0
2026-07-30	Smith Brandon S.	Officer (Chief Operating Officer)	2026-07-28	D	(78,000)	$8.56	-$667,680
2026-07-30	Smith Brandon S.	Officer (Chief Operating Officer)	2026-07-28	M	(78,000)	—	$-0
2026-07-30	Nguyen Tran	Officer (Chief Strategy Officer and CFO)	2026-07-28	M	57,000	—	$0
2026-07-30	Nguyen Tran	Officer (Chief Strategy Officer and CFO)	2026-07-28	D	(57,000)	$8.56	-$487,920
2026-07-30	Nguyen Tran	Officer (Chief Strategy Officer and CFO)	2026-07-28	M	(57,000)	—	$-0
2026-07-30	Kinney Gene G.	Director, Officer (President and CEO)	2026-07-28	M	84,000	—	$0
2026-07-30	Kinney Gene G.	Director, Officer (President and CEO)	2026-07-28	D	(84,000)	$8.56	-$719,040
2026-07-30	Kinney Gene G.	Director, Officer (President and CEO)	2026-07-28	M	(84,000)	—	$-0
2026-07-30	Kingston Anne Evans	Officer (Chief Strategy Officer)	2026-07-28	F	(3,498)	$8.56	-$29,943
2026-07-30	Isaacs Michael John	Officer (General Counsel & Company Sec.)	2026-07-28	F	(4,694)	$8.56	-$40,181
2026-06-18	SCULLY WILLIAM P	10% Owner	2026-06-16	P	20,000	$7.90	$157,990
2026-06-16	SCULLY WILLIAM P	10% Owner	2026-06-15	G	(325,000)	—	$-0
2026-06-12	SCULLY WILLIAM P	10% Owner	2026-06-11	P	125,000	$8.17	$1,021,225
2026-06-05	SCULLY WILLIAM P	10% Owner	2026-06-04	P	50,000	$9.31	$465,295
2026-06-03	SCULLY WILLIAM P	10% Owner	2026-06-02	P	50,000	$9.43	$471,300
2026-05-26	SCULLY WILLIAM P	10% Owner	2026-05-22	P	100,000	$9.81	$981,300
2026-05-15	WELCH DANIEL G	Director	2026-05-15	A	27,000	—	$0
2026-05-15	Selkoe Dennis J.	Director	2026-05-15	A	27,000	—	$0
2026-05-15	Ekman Lars	Director	2026-05-15	A	27,000	—	$0
2026-05-15	Dunn William H. Jr.	Director	2026-05-15	A	27,000	—	$0
2026-05-15	Cooke Shane	Director	2026-05-15	A	27,000	—	$0
2026-05-15	COLLIER RICHARD T	Director	2026-05-15	A	27,000	—	$0
2026-04-10	Kingston Anne Evans	Officer (Chief Strategy Officer)	2026-04-10	A	100,000	—	$0
2026-03-05	Zago Wagner M.	Officer (Chief Scientific Officer)	2026-03-03	A	190,000	—	$0
2026-03-05	Walker Karin L	Officer (Chief Accounting Officer)	2026-03-03	A	150,000	—	$0
2026-03-05	Swanson Chad J.	Officer (Chief Development Officer)	2026-03-03	A	190,000	—	$0
2026-03-05	Smith Brandon S.	Officer (Chief Operating Officer)	2026-03-03	A	190,000	—	$0
2026-03-05	Nguyen Tran	Officer (Chief Strategy Officer and CFO)	2026-03-03	A	230,000	—	$0
2026-03-05	Malecek Michael J	Officer (Chief Legal Officer)	2026-03-03	A	190,000	—	$0
2026-03-05	Kinney Gene G.	Director, Officer (President and CEO)	2026-03-03	A	520,000	—	$0
2025-07-30	Zago Wagner M.	Officer (Chief Scientific Officer)	2025-07-28	A	85,000	—	$0
2025-07-30	Walker Karin L	Officer (Chief Accounting Officer)	2025-07-28	A	25,000	—	$0
2025-07-30	Swanson Chad J.	Officer (Chief Development Officer)	2025-07-28	A	85,000	—	$0
2025-07-30	Smith Brandon S.	Officer (Chief Operating Officer)	2025-07-28	A	130,000	—	$0
2025-07-30	Nguyen Tran	Officer (Chief Strategy Officer and CFO)	2025-07-28	A	95,000	—	$0
2025-07-30	Malecek Michael J	Officer (Chief Legal Officer)	2025-07-28	A	80,000	—	$0
2025-07-30	Kinney Gene G.	Director, Officer (President and CEO)	2025-07-28	A	140,000	—	$0
2025-05-16	WELCH DANIEL G	Director	2025-05-14	A	20,183	—	$0
2025-05-16	Selkoe Dennis J.	Director	2025-05-14	A	20,183	—	$0
2025-05-16	Kim Helen Susan	Director	2025-05-14	A	20,183	—	$0
2025-05-16	Ekman Lars	Director	2025-05-14	A	20,183	—	$0
2025-05-16	Dunn William H. Jr.	Director	2025-05-14	A	20,183	—	$0
2025-05-16	Cooke Shane	Director	2025-05-14	A	20,183	—	$0
2025-05-16	COLLIER RICHARD T	Director	2025-05-14	A	20,183	—	$0
2025-05-16	Cobb Paula K	Director	2025-05-14	A	20,183	—	$0
2025-05-06	EcoR1 Capital, LLC	10% Owner	2025-05-06	S	(1,984,053)	$7.64	-$15,164,712
2025-05-06	EcoR1 Capital, LLC	10% Owner	2025-05-05	S	(977,693)	$8.11	-$7,930,166
2025-05-06	EcoR1 Capital, LLC	10% Owner	2025-05-02	S	(3,317,938)	$8.36	-$27,744,929
2025-05-02	SCULLY WILLIAM P	10% Owner	2025-01-15	G	(12,000)	—	$-0
2025-05-02	SCULLY WILLIAM P	10% Owner	2025-01-14	P	100,000	$12.79	$1,279,040
2025-05-02	SCULLY WILLIAM P	10% Owner	2025-01-03	G	(1,000)	—	$-0
2025-05-02	SCULLY WILLIAM P	10% Owner	2025-01-02	G	(13,200)	—	$-0
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-31	P	1,200	$13.37	$16,038
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-31	P	800	$13.39	$10,715
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-31	P	30,000	$12.99	$389,640
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-20	P	2,000	$15.91	$31,813
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-20	G	(500)	—	$-0
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-20	G	(40,000)	—	$-0
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-19	G	(681,000)	—	$-0
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-18	G	430,000	—	$0
2025-05-02	SCULLY WILLIAM P	10% Owner	2024-12-18	P	73,436	$13.93	$1,022,670
2025-03-07	Zago Wagner M.	Officer (Chief Scientific Officer)	2025-03-05	A	107,500	—	$0
2025-03-07	Walker Karin L	Officer (Chief Accounting Officer)	2025-03-05	A	70,000	—	$0
2025-03-07	Swanson Chad J.	Officer (Chief Development Officer)	2025-03-05	A	107,500	—	$0
2025-03-07	Smith Brandon S.	Officer (Chief Operating Officer)	2025-03-05	A	107,500	—	$0
2025-03-07	Nguyen Tran	Officer (Chief Strategy Officer and CFO)	2025-03-05	A	107,500	—	$0
2025-03-07	Malecek Michael J	Officer (Chief Legal Officer)	2025-03-05	A	107,500	—	$0
2025-03-07	Kinney Gene G.	Director, Officer (President and CEO)	2025-03-05	A	375,000	—	$0
2025-03-07	Karp Carol D.	Officer (Chief Regulatory Officer)	2025-03-05	A	107,500	—	$0
2025-03-07	Ford David A	Officer (Chief People Officer)	2025-03-05	A	107,500	—	$0
2025-02-14	Nguyen Tran	Officer (Chief Strategy Officer and CFO)	2020-04-08	J	(995)	—	$-0