UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): October 19, 2018

DECIPHERA PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

(781) 209-6400

(Registrant’s telephone number, including area code)

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 or Rule 12b-2 of the Securities Exchange Act of 1934.

Emerging growth company  ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☒

On October 19, 2018, Deciphera Pharmaceuticals, Inc. (the “Company”) announced updated preliminary results from its ongoing Phase 1 clinical study of DCC-2618, the company’s broad-spectrum KIT and PDGFRα inhibitor, in patients with gastrointestinal stromal tumors (“GIST”) at a presentation at the European Society of Medical Oncology 2018 Congress (“ESMO 2018”). The Company provided certain business updates in the materials attached as Exhibit 99.1 to this Current Report on Form 8-K and incorporated by reference herein.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits.

INDEX TO EXHIBITS

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Exhibit 99.1

Corporate Update

DCC-2618

Ongoing Phase 1 Trial Update

We are studying DCC-2618 in an ongoing Phase 1 trial in patients with advanced malignancies, including gastrointestinal stromal tumors, or GIST. Our ongoing Phase 1 trial is comprised of two parts: a dose escalation portion and a dose expansion portion, as detailed below:

Part 1: Dose Escalation

Part 2: Dose Expansion

European Society of Medical Oncology (ESMO) 2018 Congress and Additional Interim Results

On October 19, 2018, Deciphera Pharmaceuticals, Inc., or the Company, announced updated preliminary results from its ongoing Phase 1 clinical study of DCC-2618, the Company’s broad-spectrum KIT and PDGFRα inhibitor, in patients with GIST at a presentation at the European Society of Medical Oncology 2018 Congress, or ESMO 2018.

The chart below summarizes the demographic profile of the patients for whom data was presented at ESMO 2018:

Phase 1 Demographics and Baseline Characteristics of GIST Patients

Notes: (1) Mean number of prior regimens for ³4th line patients was 3.6.

At ESMO 2018, we reported preliminary results with a cutoff date of August 31, 2018 that include investigator-assessed median progression free survival, or mPFS, objective response rates by best response, or ORR, and disease control rates at 3 months, or DCR, as determined by Response Evaluation Criteria in Solid Tumors, or RECIST, version 1.1 across 178 patients receiving DCC-2618 at doses of >100mg daily.

Preliminary results, including those presented at ESMO 2018, are summarized in the below table.

Notes: (1) Includes nine unconfirmed responses: 2^nd line (n=1), 3^rd line (n=3) and ³4th line (n=5); (2) Does not reflect one PR reported after cutoff date, which would result in an ORR in 2^nd line of 21% and an ORR in 2^nd line and 3^rd line combined of 22%; (3) Excludes five patients due to missing data at the time of data cutoff (n=2), lack of first tumor assessment (n=1), withdrawal of consent prior to first assessment (n=1) and unrelated death at C1D4 prior to first assessment (n=1); (4) 59 of 67 combined 2^nd line and 3^rd line patients received 150mg once daily; (5) Censored patients for mPFS were 2^nd line (58%), 3^rd line (52%), 4^th line and 4^th line plus (35%) and 2^nd and 3^rd line (55%); (6) As of the cutoff date, active patients by line of therapy were as follows: 2^nd line were 61%; 3^rd line were 59%; 4^th line and 4^th line plus were 44% and 2^nd and 3^rd line were 60%; and (7) Median Treatment Duration for 2^nd line is 48 weeks, for 3^rd line is NR, for 4^th line and 4^th line plus is 28 weeks and for 2^nd and 3^rd line is 52 weeks. Includes 14 patients who elected for intra-patient dose escalation.

Preliminary ORR Data by Best Response with DCC-2816 @ ³ 100 mg/d

At ESMO 2018, for the second- and third-line GIST patients in our Phase 1 trial of DCC-2618 who received both a baseline and post-treatment CT scan by the efficacy cutoff date (n = 67), we presented the greatest reduction or smallest increase in tumor size from baseline as measured by CT or MRI scan, or best response, for solid malignancies per RECIST as shown in the following figure.

Best Response per RECIST⁽¹⁾⁽²⁾

In Second- and Third-Line KIT & PDGFRα

Patients Receiving ³ 100 mg/d (n=67)

Notes: (1) Based on cutoff date of August 31, 2018; RECIST data per investigator assessment; (2) Includes unconfirmed responses in 2nd line (n=1) and 3rd line (n=3). Does not reflect one PR in 2nd line reported after cutoff date. Includes 14 patients who elected for intra-patient dose escalation.

Preliminary mPFS Data in GIST Patients with DCC-2816 @ ³ 100 mg/d

At ESMO 2018, for the second-, third- and fourth- and fourth-line plus GIST patients in our Phase 1 trial of DCC-2618, we presented preliminary mPFS data for patients receiving doses of ³100mg daily as shown in the following figures.

Tumor Control per RECIST⁽¹⁾

KIT & PDGFRα Patients at ³ 100 mg/d (n=178)

Notes: (1) Based on cutoff date of August 31, 2018; RECIST data per investigator assessment; (2) PFS at 52 weeks was 32% for 2^nd Line and 47% for 3^rd Line.

Duration of Treatment of GIST Patients in Ongoing Phase 1 Trial

The following figure shows the duration of treatment with DCC-2618, as of the cutoff date, for second- and third-line GIST patients in the Phase 1 trial who had received ³ 100 mg of DCC-2618 daily. In the second-line GIST patients, as of the cutoff date, 17 patients received DCC-2618 at doses of ³100mg daily for more than 6 months with 65% (11 of 17) of these patients remaining on study. In third-line GIST patients, as of the cutoff date, 20 patients received DCC-2618 at doses of ³100mg daily for more than 6 months with 75% (15 of 20) of these patients remaining on study.

Preliminary Data with DCC-2618 at ³ 100 mg Daily Shows Emerging Durability

Notes: (1) Based on cutoff date of August 31, 2018; RECIST data per investigator assessment; (2) Includes unconfirmed responses in 2nd line (n=1) and 3rd line (n=3). Does not reflect one PR in 2nd line reported after cutoff date. Includes 14 patients who elected for intra-patient dose escalation.

In addition to the data presented at ESMO 2018, we also observed the following in the fourth-line and fourth-line-plus GIST patients. As of the cutoff date, of the 46 combined fourth- and fourth-line plus GIST patients that received DCC-2618 at doses of ³100mg daily for more than 6 months, 74% (34 of 46) of these patients remained on study.

Tolerability Results in Phase 1 Trial

DCC-2618 was generally well tolerated at all doses administered and the treatment-emergent adverse events by Grades 1/2 and Grades 3/4 are summarized in the tables below.

For the 178 GIST patients treated at doses above ³100mg daily, DCC-2618 was generally well tolerated. Among the treatment-emergent adverse events, or TEAEs, reported by investigators (>10%), regardless of relationship to DCC-2618, the most common were: alopecia (50%), myalgia (44%), fatigue (43%), constipation (34%), hand-foot skin reaction (32%), nausea (30%), decreased appetite (28%), weight decreased (24%), abdominal pain (23%), diarrhea (23%) and lipase increase (23%). Clinically asymptomatic lipase elevations were the most frequent Grade 3 TEAE. Among the 178 GIST patients treated at doses of >100mg daily: 14% (24 patients) experienced dose reductions due to TEAEs and 11% (19 patients) experienced treatment discontinuations due to TEAEs.

Treatment Emergent Adverse Events

in ³ 10% of GIST Patients at ³ 100mg Daily (n = 178)

Notes: Data presented at ESMO 2018 based on cutoff as of August 31, 2018. (1) Palmar-plantar erythrodysaesthesia syndrome reported in 19 patients.

For 142 GIST patients treated at 150 mg daily, DCC-2618 was also generally well tolerated. Clinically asymptomatic lipase elevations were the most frequent Grade 3 treatment-emergent adverse event. Among the 142 GIST patients treated at 150 mg daily: 13% (18) patients experienced dose reductions due to TEAEs and 11% (15) experienced treatment discontinuations due to TEAEs.

Treatment Emergent Adverse Events

in ³ 10% of GIST Patients at 150mg Daily (n = 142)

Note: Data presented at ESMO 2018 based on cutoff as of August 31, 2018. (1) Palmar-plantar erythrodysaesthesia syndrome reported in 18 patients.

Planned Phase 3 Trial INTRIGUE

We expect to initiate our planned randomized (1:1) open label Phase 3 trial, INTRIGUE, comparing treatment with DCC-2618 at 150mg daily to sunitinib at 50mg daily in up to 358 second-line GIST patients, in the fourth quarter of 2018.

Our Drug Candidates - Pipeline

We currently retain global development and commercialization rights to our drug candidates, including the lead programs summarized in the following figure:

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This document contains forward-looking statements, which reflect our current views with respect to, among other things, our clinical programs, operations and financial performance. All statements other than statements of historical facts contained in this document, including statements regarding our strategy, future operations, future clinical programs, future financial position, future revenue, projected costs, prospects, plan, objectives of management and expected growth are forward-looking statements. You can identify these forward-looking statements by the use of words such as “outlook,” “believes,” “expects,” “potential,” “continues,” “may,” “will,” “should,” “seeks,” “approximately,” “predicts,” “intends,” “plans,” “estimates,” “anticipates” or the negative version of these words or other comparable words. Such forward-looking statements are subject to various risks and uncertainties. Accordingly, there are or will be important factors that could cause actual outcomes or results to differ materially from those indicated in these statements. We believe these factors include but are not limited to those described under “Risk Factors” in our Quarterly Report on Form 10-Q for the quarter ended June 30, 2018 and include, among other things:

These factors should not be construed as exhaustive and should be read in conjunction with the other cautionary statements that are included elsewhere in our filings with the SEC. The forward-looking statements contained in this document are made as of the date of this document, and we undertake no obligation to publicly update or review any forward-looking statement, whether as a result of new information, future developments or otherwise.