Rigel Pharmaceuticals Provides Business Update - REZLIDHIA U.S. FDA approval and commercial launch for the treatment of adult patients with relapsed or refractory AML with susceptible IDH1 mutation - Preliminary fourth q

Rigel Pharmaceuticals Provides Business Update

- REZLIDHIA U.S. FDA approval and commercial launch for

the treatment of adult patients with relapsed or refractory AML with susceptible IDH1 mutation

- Preliminary fourth quarter 2022 Total Revenue of approximately

$51.3 million which includes TAVALISSE preliminary net product sales of approximately $21.9 million and REZLIDHIA preliminary

net product sales of approximately $0.9 million

- Continued global expansion of TAVALISSE in ITP with Japan PMDA

approval for partner Kissei

SOUTH SAN FRANCISCO,

Calif., Jan. 9, 2023 /PRNewswire/ -- Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) today provided a business update including preliminary

total revenue for the fourth quarter, ongoing activity from the commercial portfolio, including TAVALISSE (fostamatinib

disodium hexahydrate) tablets and REZLIDHIA (olutasidenib) capsules, and upcoming catalysts for 2023.

"2022 was a transformative

year for Rigel. We expanded our commercial hematology-oncology portfolio with the FDA approval and commercial launch of REZLIDHIA during

December, and fourth quarter TAVALISSE net product sales reached a new high," said Raul Rodriguez, Rigel's president and CEO. "As

we look ahead to 2023, we are executing on the commercial launch of REZLIDHIA to bring this important new therapy to patients in need.

We continue to drive growth for TAVALISSE ITP sales in the U.S., while working with our partners to expand its global reach. We remain

committed to building our hematology-oncology franchise and advancing our pipeline programs."

Preliminary Financial Update

In the fourth quarter

of 2022, a total of 2,417 bottles of TAVALISSE were sold in the U.S., 2,196 of which were shipped directly to patients and clinics, representing

the highest daily bottles shipped to patients and clinics in a quarter since launch. While Rigel is still determining final results for

the fourth quarter of 2022, it expects to report net product sales of TAVALISSE of $21.9 million for the fourth quarter compared to $17.6

million for the same period of 2021.

REZLIDHIA became commercially

available in the U.S. on December 22, 2022. In the fourth quarter of 2022, a total of 64 bottles of REZLIDHIA were sold in the U.S. to

fill initial orders from our distributors, 2 of which were shipped to patients and clinics. While Rigel is still determining final results

for the fourth quarter of 2022, it expects to report net product sales of REZLIDHIA of $0.9 million for the fourth quarter.

Contract revenues for the fourth quarter

of 2022 are expected to be approximately $28.5 million, consisting of $26.5 million in contract revenue from collaborations and $2.0

million in government contract revenue. Contract revenue from collaborations includes a $20.0 million milestone earned from Kissei Pharmaceutical

Co., Ltd. (Kissei) upon Japan's Pharmaceuticals and Medical Devices Agency (PMDA) approval of TAVALISSE for the treatment of chronic

ITP, $5.7 million in non-cash revenue from its collaboration agreement with Medison Pharma Trading AG, $0.6 million in royalty revenue

from Grifols, and $0.2 million in revenue related to its license agreements with Eli Lilly and Grifols.

For the fourth quarter of 2022, Rigel expects

to report total revenue of approximately $51.3 million.

For the fourth quarter of 2022, Rigel expects

its cost of product sales to include a 15% royalty on its REZLIDHIA net product sales.

to report cash, cash equivalents, and short-term investments as of December 31, 2022, of approximately $58.2 million compared to $125.0

million as of December 31, 2021. Additionally, Rigel expects to receive the $20.0 million milestone payment from Kissei during the first

The above information

is preliminary, has not been audited, and is subject to change upon the audit of the company's financial statements for the year ended

December 31, 2022. Rigel expects to provide complete fourth quarter and full year 2022 financial results in March 2023.

In patients with ITP

(immune thrombocytopenia), the immune system attacks and destroys the body's own blood platelets, which play an active role in blood

clotting and healing. Common symptoms of ITP are excessive bruising and bleeding. People suffering with chronic ITP may live with an

increased risk of severe bleeding events that can result in serious medical complications or even death. Current therapies for ITP include

steroids, blood platelet production boosters (TPO-RAs), and splenectomy. However, not all patients respond to existing therapies. As

a result, there remains a significant medical need for additional treatment options for patients with ITP.

Acute myeloid leukemia

(AML) is a rapidly progressing cancer of the blood and bone marrow that affects myeloid cells, which normally develop into various types

of mature blood cells. AML occurs primarily in adults and accounts for about 1 percent of all adult cancers. The American Cancer Society

estimates that in the United States alone, there will be about 20,050 new cases, most in adults, in 2022.2

Relapsed AML affects

about half of all patients who, following treatment and remission, experience a return of leukemia cells in the bone marrow.3

Refractory AML, which affects between 10 and 40 percent of newly diagnosed patients, occurs when a patient fails to achieve remission

even after intensive treatment.4 Quality of life declines for patients with each successive line of treatment for AML, and

well-tolerated treatments in relapsed or refractory disease remain an unmet need.

REZLIDHIA is indicated for the treatment of adult patients with relapsed

or refractory acute myeloid leukemia (AML) with a susceptible isocitrate dehydrogenase-1 (IDH1) mutation as detected by an FDA-approved

IMPORTANT SAFETY INFORMATION

WARNING: DIFFERENTIATION SYNDROME

Differentiation syndrome, which can be fatal,

can occur with REZLIDHIA treatment. Symptoms may include dyspnea, pulmonary infiltrates/pleuropericardial effusion, kidney injury, hypotension,

fever, and weight gain. If differentiation syndrome is suspected, withhold REZLIDHIA and initiate treatment with corticosteroids and

hemodynamic monitoring until symptom resolution.

WARNINGS AND PRECAUTIONS

Differentiation Syndrome

REZLIDHIA can cause differentiation syndrome.

In the clinical trial of REZLIDHIA in patients with relapsed or refractory AML, differentiation syndrome occurred in 16% of patients,

with grade 3 or 4 differentiation syndrome occurring in 8% of patients treated, and fatalities in 1% of patients. Differentiation syndrome

is associated with rapid proliferation and differentiation of myeloid cells and may be life-threatening or fatal. Symptoms of differentiation

syndrome in patients treated with REZLIDHIA included leukocytosis, dyspnea, pulmonary infiltrates/pleuropericardial effusion, kidney

injury, fever, edema, pyrexia, and weight gain. Of the 25 patients who experienced differentiation syndrome, 19 (76%) recovered after

treatment or after dose interruption of REZLIDHIA. Differentiation syndrome occurred as early as 1 day and up to 18 months after REZLIDHIA

initiation and has been observed with or without concomitant leukocytosis.

If differentiation syndrome is suspected, temporarily

withhold REZLIDHIA and initiate systemic corticosteroids (e.g., dexamethasone 10 mg IV every 12 hours) for a minimum of 3 days and until

resolution of signs and symptoms. If concomitant leukocytosis is observed, initiate treatment with hydroxyurea, as clinically indicated.

Taper corticosteroids and hydroxyurea after resolution of symptoms. Differentiation syndrome may recur with premature discontinuation

of corticosteroids and/or hydroxyurea treatment. Institute supportive measures and hemodynamic monitoring until improvement; withhold

dose of REZLIDHIA and consider dose reduction based on recurrence.

hepatotoxicity, presenting as increased alanine aminotransferase (ALT), increased aspartate aminotransferase (AST), increased blood alkaline

phosphatase, and/or elevated bilirubin. Of 153 patients with relapsed or refractory AML who received REZLIDHIA, hepatotoxicity occurred

in 23% of patients; 13% experienced grade 3 or 4 hepatotoxicity. One patient treated with REZLIDHIA in combination with azacitidine in

the clinical trial, a combination for which REZLIDHIA is not indicated, died from complications of drug-induced liver injury. The median

time to onset of hepatotoxicity in patients with relapsed or refractory AML treated with REZLIDHIA was 1.2 months (range: 1 day to 17.5

months) after REZLIDHIA initiation, and the median time to resolution was 12 days (range: 1 day to 17 months). The most common hepatotoxicities

were elevations of ALT, AST, blood alkaline phosphatase, and blood bilirubin.

Monitor patients frequently for clinical

symptoms of hepatic dysfunction such as fatigue, anorexia, right upper abdominal discomfort, dark urine, or jaundice. Obtain

baseline liver function tests prior to initiation of REZLIDHIA, at least once weekly for the first two months, once every other week

for the third month, once in the fourth month, and once every other month for the duration of therapy. If hepatic dysfunction

occurs, withhold, reduce, or permanently discontinue REZLIDHIA based on recurrence/severity.

The most common ( 20%) adverse reactions,

including laboratory abnormalities, were aspartate aminotransferase increased, alanine aminotransferase increased, potassium decreased,

sodium decreased, alkaline phosphatase increased, nausea, creatinine increased, fatigue/malaise, arthralgia, constipation, lymphocytes

increased, bilirubin increased, leukocytosis, uric acid increased, dyspnea, pyrexia, rash, lipase increased, mucositis, diarrhea and

Advise women not to breastfeed during treatment

with REZLIDHIA and for 2 weeks after the last dose.