On this page of StockholderLetter.com we present the latest annual shareholder letter from Kiniksa Pharmaceuticals, Ltd. — ticker symbol KNSA. Reading current and past KNSA letters to shareholders can bring important insights into the investment thesis.
Vanessa Jill Living with Recurrent Pericarditis 2025 A N N U A L R E P O R T Jo o
Dear Fellow Shareholders, In 2025, Kiniksa continued to deliver meaningful progress across our commercial and clinical portfolio, helping patients suffering from debilitating diseases with significant unmet need. Continued ARCALYST commercial growth and disciplined capital allocation position Kiniksa for near- and long-term success. We are building the foundation for future growth through strategic investments in the commercialization of ARCALYST as well as the advancement of our pipeline of interleukin-1 alpha (IL-1 ) and interleukin-1 beta (IL-1 ) inhibition assets. ARCALYST ARCALYST, an IL-1 & IL-1 cytokine trap, is the only U.S. Food and Drug Administration (FDA)-approved therapy for the treatment of recurrent pericarditis and reduction in risk of recurrence. In the five years since launch, ARCALYST has redefined the treatment paradigm for this disease, establishing IL-1 pathway inhibition as the preferred second-line approach, ahead of corticosteroids. In August 2025, the American College of Cardiology formally recognized this evolution with the publication of its Concise Clinical Guidance, recommending IL-1 pathway inhibition after the use of NSAIDs and colchicine for patients suffering from recurrent pericarditis. Expanding adoption of IL-1 & IL-1 inhibition with ARCALYST was the primary driver of our robust commercial performance throughout 2025. Over the course of the year, we saw meaningful increases in the breadth and depth of prescribing, treatment duration, and penetration across the recurrent pericarditis population. More than 4,150 healthcare providers have prescribed ARCALYST since launch, with approximately 29% writing more than one prescription. Importantly, the majority of new prescriptions are coming from existing prescribers, speaking to the effectiveness of our educational efforts and the growing appreciation physicians have for ARCALYST as a safe and effective treatment that can be used continuously throughout the duration of this chronic disease. Average total duration of therapy continues to grow and is approaching 3 years, in line with the median duration of disease. As a result, approximately 18% of the annual target population of 14,000 patients with multiple recurrences were actively on ARCALYST treatment as of the end of 2025. Furthermore, growing physician familiarity prescribing ARCALYST is contributing to broader use in patients on their first recurrence, who account for around 20% of ARCALYST prescriptions. The upside potential within the additional 26,000 patients each year who experience their first recurrence is large, particularly among those suffering from additional risk factors associated with longer disease duration. ARCALYST sales grew 62% year-over-year to $677.6 million in 2025, and we believe substantial opportunity remains. Our strong and profitable commercial collaboration positions us to enable the next phase of growth for ARCALYST. We continue to make disciplined investments to maximize our opportunity in recurrent pericarditis by efficiently reaching additional patients and physicians. Alongside our field force, we are advancing digital marketing initiatives to promote patient self-advocacy and AI-driven targeting to position our field personnel for timely engagement with physicians. We are also evaluating opportunities to further expand the impact of Pericardial Disease Centers (PDCs), where ARCALYST adoption continues to outpace that of other sites. As of the end of 2025, there were 18 PDCs across the U.S. specializing in recurrent pericarditis. As the market leader, we are leveraging our existing clinical expertise to explore additional efficacious treatment options for patients. With this program, we are advancing a validated mechanism that could address key patient needs and expand penetration into the addressable market. We believe KPL-387 could enable once-monthly dosing with a single subcutaneous self-injection in a liquid formulation, offering convenient administration using an autoinjector. In 2025, we initiated the registrational Phase 2/3 development program of KPL-387 in recurrent pericarditis, with Phase 2 data expected in the second half of 2026. We are also conducting a supplemental Phase 2 Transition to KPL-387 Monotherapy Dosing & Administration Study to provide healthcare professionals with additional information at the time of launch to support initiating KPL-387. Market research indicates there may be strong demand among the vast majority of surveyed patients and healthcare professionals for a highly efficacious IL-1 & IL-1 inhibitor with the target profile of KPL-387. Approximately 75% of surveyed recurrent pericarditis patients would prefer a treatment with such a target profile over currently available or other investigational therapies. Additionally, among ARCALYST-na ve patients, approximately 75% stated an increased willingness to take an injectable therapy if presented in an autoinjector. On the physician side, approximately 92% indicated a high likelihood of prescribing the KPL-387 target profile for new patients, in the context of available commercial and investigational therapies. Both patient and physician preferences highlight the potential for KPL-387 to address key needs for those with recurrent pericarditis. In October 2025, the FDA granted Orphan Drug Designation to KPL-387 for the treatment of pericarditis, including recurrent pericarditis. We are working diligently to bring this potential treatment option to patients and are aiming to be on the market in the 2028/2029 timeframe. KPL-1161 KPL-1161 is an Fc-modified monoclonal antibody IL-1 & IL-1 antagonist developed independently by Kiniksa that binds IL-1R1, with a target profile of once-quarterly subcutaneous dosing. We believe this profile may support treatment across a range of cardiovascular and IL-1 mediated diseases. KPL-1161 is currently in preclinical development, and we expect to initiate a Phase 1 first-in-human trial by the end of 2026. Financial Position Through consistent execution and prudent capital allocation, Kiniksa has maintained a robust balance sheet with positive annual cash flow. Our financial strength provides capacity to continue investing responsibly in value creation by maximizing the opportunity with ARCALYST, advancing our clinical pipeline, and pursuing business development initiatives, which remain fundamental to our strategy. Alongside our existing assets, we continue to evaluate opportunities to expand our portfolio with programs that have strong biologic rationale and validated mechanisms. Supported by the relentless devotion of Kiniksa s employees, we are well-positioned to drive future success, generate long-term value, and help many more patients in need. Thank you for your ongoing support. Every Second Counts! Additionally, we are committed to ongoing innovation with ARCALYST and continue to support a collaborative Phase 2 study in cardiac sarcoidosis conducted by Mayo Clinic and The Johns Hopkins University. Sincerely, KPL-387 CEO and Chairman of the Board KPL-387, our independently developed monoclonal antibody that binds human interleukin-1 receptor 1 (IL-1R1) to inhibit the signaling activity of the cytokines IL-1 & IL-1 , represents a meaningful opportunity to build on our leadership in recurrent pericarditis. Sanj K. Patel
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 • Benford's Law Stocks icon KNSA Benford's Law Stock Score = 74


KNSA Shareholder/Stockholder Letter Transcript:

Vanessa
Jill
Living with Recurrent Pericarditis
2025
A N N U A L
R E P O R T
Jo  o

Dear Fellow Shareholders,
In 2025, Kiniksa continued to deliver meaningful progress across our
commercial and clinical portfolio, helping patients suffering from
debilitating diseases with significant unmet need.
Continued ARCALYST commercial growth and disciplined capital
allocation position Kiniksa for near- and long-term success. We are
building the foundation for future growth through strategic investments
in the commercialization of ARCALYST as well as the advancement of
our pipeline of interleukin-1 alpha (IL-1  ) and interleukin-1 beta (IL-1  )
inhibition assets.
ARCALYST
ARCALYST, an IL-1   & IL-1   cytokine trap, is the only U.S. Food and
Drug Administration (FDA)-approved therapy for the treatment of
recurrent pericarditis and reduction in risk of recurrence. In the five
years since launch, ARCALYST has redefined the treatment paradigm
for this disease, establishing IL-1 pathway inhibition as the preferred
second-line approach, ahead of corticosteroids. In August 2025, the
American College of Cardiology formally recognized this evolution with
the publication of its Concise Clinical Guidance, recommending IL-1
pathway inhibition after the use of NSAIDs and colchicine for patients
suffering from recurrent pericarditis.
Expanding adoption of IL-1   & IL-1   inhibition with ARCALYST was the
primary driver of our robust commercial performance throughout
2025. Over the course of the year, we saw meaningful increases in the
breadth and depth of prescribing, treatment duration, and penetration
across the recurrent pericarditis population. More than 4,150 healthcare
providers have prescribed ARCALYST since launch, with approximately
29% writing more than one prescription. Importantly, the majority of
new prescriptions are coming from existing prescribers, speaking to the
effectiveness of our educational efforts and the growing appreciation
physicians have for ARCALYST as a safe and effective treatment that can
be used continuously throughout the duration of this chronic disease.
Average total duration of therapy continues to grow and is approaching
3 years, in line with the median duration of disease. As a result,
approximately 18% of the annual target population of 14,000 patients with
multiple recurrences were actively on ARCALYST treatment as of the end
of 2025. Furthermore, growing physician familiarity prescribing ARCALYST
is contributing to broader use in patients on their first recurrence, who
account for around 20% of ARCALYST prescriptions. The upside potential
within the additional 26,000 patients each year who experience their
first recurrence is large, particularly among those suffering from
additional risk factors associated with longer disease duration.
ARCALYST sales grew 62% year-over-year to $677.6 million in 2025, and
we believe substantial opportunity remains.
Our strong and profitable commercial collaboration positions us to
enable the next phase of growth for ARCALYST. We continue to make
disciplined investments to maximize our opportunity in recurrent
pericarditis by efficiently reaching additional patients and physicians.
Alongside our field force, we are advancing digital marketing initiatives
to promote patient self-advocacy and AI-driven targeting to position
our field personnel for timely engagement with physicians. We are also
evaluating opportunities to further expand the impact of Pericardial
Disease Centers (PDCs), where ARCALYST adoption continues to
outpace that of other sites. As of the end of 2025, there were 18 PDCs
across the U.S. specializing in recurrent pericarditis.
As the market leader, we are leveraging our existing clinical expertise to
explore additional efficacious treatment options for patients. With this
program, we are advancing a validated mechanism that could address
key patient needs and expand penetration into the addressable market.
We believe KPL-387 could enable once-monthly dosing with a single
subcutaneous self-injection in a liquid formulation, offering convenient
administration using an autoinjector. In 2025, we initiated the
registrational Phase 2/3 development program of KPL-387 in recurrent
pericarditis, with Phase 2 data expected in the second half of 2026.
We are also conducting a supplemental Phase 2 Transition to KPL-387
Monotherapy Dosing & Administration Study to provide healthcare
professionals with additional information at the time of launch to
support initiating KPL-387.
Market research indicates there may be strong demand among the
vast majority of surveyed patients and healthcare professionals for a
highly efficacious IL-1   & IL-1   inhibitor with the target profile of KPL-387.
Approximately 75% of surveyed recurrent pericarditis patients would
prefer a treatment with such a target profile over currently available
or other investigational therapies. Additionally, among ARCALYST-na  ve
patients, approximately 75% stated an increased willingness to take an
injectable therapy if presented in an autoinjector. On the physician side,
approximately 92% indicated a high likelihood of prescribing the KPL-387
target profile for new patients, in the context of available commercial
and investigational therapies. Both patient and physician preferences
highlight the potential for KPL-387 to address key needs for those with
recurrent pericarditis.
In October 2025, the FDA granted Orphan Drug Designation to KPL-387
for the treatment of pericarditis, including recurrent pericarditis. We are
working diligently to bring this potential treatment option to patients
and are aiming to be on the market in the 2028/2029 timeframe.
KPL-1161
KPL-1161 is an Fc-modified monoclonal antibody IL-1   & IL-1   antagonist
developed independently by Kiniksa that binds IL-1R1, with a target
profile of once-quarterly subcutaneous dosing. We believe this profile
may support treatment across a range of cardiovascular and IL-1
mediated diseases. KPL-1161 is currently in preclinical development, and
we expect to initiate a Phase 1 first-in-human trial by the end of 2026.
Financial Position
Through consistent execution and prudent capital allocation, Kiniksa
has maintained a robust balance sheet with positive annual cash
flow. Our financial strength provides capacity to continue investing
responsibly in value creation by maximizing the opportunity with
ARCALYST, advancing our clinical pipeline, and pursuing business
development initiatives, which remain fundamental to our strategy.
Alongside our existing assets, we continue to evaluate opportunities to
expand our portfolio with programs that have strong biologic rationale
and validated mechanisms.
Supported by the relentless devotion of Kiniksa   s employees, we are
well-positioned to drive future success, generate long-term value, and
help many more patients in need. Thank you for your ongoing support.
Every Second Counts!
Additionally, we are committed to ongoing innovation with ARCALYST
and continue to support a collaborative Phase 2 study in cardiac
sarcoidosis conducted by Mayo Clinic and The Johns Hopkins University.
Sincerely,
KPL-387
CEO and Chairman of the Board
KPL-387, our independently developed monoclonal antibody that binds
human interleukin-1 receptor 1 (IL-1R1) to inhibit the signaling activity of
the cytokines IL-1   & IL-1  , represents a meaningful opportunity to build
on our leadership in recurrent pericarditis.
Sanj K. Patel


shareholder letter icon 4/16/2026 Letter Continued (Full PDF)
 

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