Neoadjuvant Pembrolizumab + Epacadostat Prior to Curative Surgical Care for Squamous Cell Carcinoma of the Head and Neck

The KEO study is a single arm phase II trial including 44 patients with T1N1-2B, T2N0-N2B
head and neck squamous cell carcinoma (HNSCC) eligible for curative-intent resection (+/-
adjuvant therapy), who receive neo-adjvuant pembrolizumab + epacadostat. Patients that fit
the inclusion criteria (see detailed eligibility criteria below) will receive neoadjuvant
immunotherapy either with anti-PD-1 (pembrolizumab) alone or anti-PD-1 in combination with
IDO1 inhibition (epacadostat). Patients will receive 200 mg IV Pembrolizumab every 3 weeks
for up to 3 doses over a period of 8 weeks as well as oral epacadostat 100 mg BID starting on
day 1 for the duration of pembrolizumab treatment.

All patients will undergo baseline biopsy (mandatory, sampling ≥ 4 areas to represent the
tumor), as well as baseline imaging (and for exploratory analysis collection of blood for
baseline ctDNA testing and TCR analysis). Patients who are unable to safely (or for other
reasons unwilling to undergo biopsy at baseline and on treatment 3-4 weeks in for infiltrate
assessment are not eligible for the study. MRI is the preferred imaging modality; however,
diagnostic CT is acceptable if patient is unable to undergo MRI or as clinically indicated.

Subsequently at week 3-4 an interim assessment will be performed:

1. All patients will undergo imaging with a 2nd MRI scan (or CT, to match prior imaging).

2. All patients will also undergo repeat mandatory on-treatment biopsy consisting of of 4-6
representative samples to compare to the baseline biopsy. Adequacy of response to
treatment will be assessed in assessing eradication of tumor/presence of antitumor tumor
response (analogous to reports in lung cancer (Forde et al ESMO 2016). The on-treatment
biopsy is essential in the assessment of early response and decision to extend
neo-adjuvant treatment to 8 weeks is based in large part on this biopsy. In patients
where an on-treatment biopsy is not obtained (e.g no longer considered safe or status of
patient has changed), patients will automatically be considered non-complete responders,
and take off study after 4 weeks (with the very unlikely but possible exceptions of
complete response radiologic response at 4 weeks imaging).

3. For exploratory purposes, blood will also be drawn for repeat ctDNA and TCR analysis in
order to assess potential suitability of dynamic changes ctDNA or TCR
clonality/diversity as candidate biomarkers for follow-up studies.

At the week 3/4 interim assessment, results of the imaging and biopsy will be used to
determine response and to determine continuation of immunotherapy induction treatment for up
to 8 weeks (full immunotherapy induction course). Patients that demonstrate stable disease or
tumor shrinkage radiographically and biopsy demonstrating dense lymphocytic infiltrate with
dying tumor / decrease in residual viable tumor will continue on protocol.

Those patients with lack of lymphocytic infiltrate/dying tumor or increasing tumor on
radiology (and confirmed on pathology from 2nd biopsy) will be transitioned to standard of
care treatment with early salvage surgery or chemoradiation (as clinically indicated).

Pre-surgery assessment: For those patients continuing - a second confirmatory scan will be
done 3-4 weeks later again coupled with a blood draw, and followed by surgery at/around week
8 (+/-1 week depending on operating schedules).

Definitive surgery will be done at week 8. Surgical specimens will again be evaluated for
percentage residual viable tumor and inflammatory infiltrate. Patients that exhibit complete
pathologic response (no viable tumor) will follow close observation with repeat imaging
(CT/MRI at 4-6 weeks), clinical exams and a PET scan at 12 weeks post-surgery (as well as
serial ctDNA draws (exploratory).

Patients with major pathologic responses (≤10% residual tumor, but tumor present) will be
treated with de-escalated adjuvant radiation therapy as determined by the tumor
board/radiation oncology.

Patients with a surgical specimen that demonstrates >10% residual tumor after surgery will
undergo standard adjuvant RT/CRT as indicated.

Adjuvant Phase: Patients will continue adjuvant pembrolizumab plus epacadostat every 3 weeks
for 12 months and be monitored with ctDNA and imaging.

Inclusion Criteria:

- Be willing and able to provide written informed consent/assent for the trial.

- Be 18 years of age or older on day of signing informed consent.

- Patients with non-bulky/non-bulky squamous cell carcinomas of the head and neck, with
an indication for surgical therapy.

1. T1N1-N2B, T2-4N0-N2b stage are generally eligible

2. If determined per tumor board that a low-volume/non-bulky tumor of another stage
is appropriate for resection (e.g. small volume T4 with a small amount of bone
invasion) such tumors may also be considered for this study if recommendation in
tumor board is such.

- Be appropriate candidates for resection and curative intent therapy in general.

- Have a performance status of 0 or 1 on the ECOG Performance Scale.

- Consent to undergo biopsy from a newly obtained core or excisional biopsy of a tumor
lesion before study drug administration, and during treatment. Biopsy in case of
progressive disease is optional.

- Ability to swallow tablets (at future point administration via G-tube may be allowed
if approved by drug manufacturer)

- Measurable disease per RECIST 1.1.

- Known HPV status for oropharyngeal primary tumors.

- Pre-operative scans including MRI/CT neck and, CT chest with contrast. If contrast is
contraindicated, Staging PET or PET-CT is acceptable although high quality /
diagnostic cross-sectional imaging of the head and neck area is recommended.

- Demonstrate adequate organ function as defined in Table 1, all screening labs should
be performed within 10 days of treatment initiation.

Table 1 Adequate Organ Function Laboratory Values System Laboratory Value Hematological
Absolute neutrophil count (ANC) ≥1,500 /mcL Platelets ≥100,000 / mcL Hemoglobin ≥9 g/dL or
≥5.6 mmol/L without transfusion or EPO dependency (within 7 days of assessment) Renal Serum
creatinine OR within upper limit of normal (ULN) OR

Measured or calculateda creatinine clearance ≥60 mL/min for subject with creatinine (GFR
can also be used in place of creatinine or levels > institutional ULN CrCl)

Hepatic Serum total bilirubin ≤ 1.5 X ULN OR Direct bilirubin ≤ ULN for subjects with total
bilirubin levels > 1.5 ULN

AST (SGOT) and ALT (SGPT) ≤ 2.5 X ULN

Albumin >2.5 mg/dL

Coagulation International Normalized Ratio (INR) or ≤1.5 X ULN unless subject is receiving
Prothrombin Time (PT) anticoagulant therapy as long as PT or PTT is within therapeutic
range of intended use of anticoagulants

Activated Partial Thromboplastin Time (aPTT) ≤1.5 X ULN unless subject is receiving
anticoagulant therapy as long as PT or PTT is within therapeutic range of intended use of
anticoagulants aCreatinine clearance should be calculated per institutional standard.

- Female subject of childbearing potential should have a negative urine or serum
pregnancy within 72 hours prior to receiving the first dose of study medication. If
the urine test is positive or cannot be confirmed as negative, a serum pregnancy test
will be required.

- Female subjects of childbearing potential should be willing to use 2 methods of birth
control or be surgically sterile, or abstain from heterosexual activity for the course
of the study through 120 days after the last dose of study medication. Subjects of
childbearing potential are those who have not been surgically sterilized or have not
been free from menses for > 1 year.

- Male subjects should agree to use an adequate method of contraception starting with
the first dose of study therapy through 120 days after the last dose of study therapy.
Abstinence is considered an adequate contraception method.

Exclusion Criteria:

- Has a diagnosis now or in the past of immunodeficiency requiring systemic steroid
therapy in excess of physiologic dose (or any other form of immunosuppressive therapy
within 10 days prior to the first dose of trial treatment).

- Has bulky tumor (define as N3 lymph node or equivalent lymph conglomerate (≥ 6 cm in
one dimension), or primary tumor > 4 cm). Cystic HPV+ lymph nodes should be assessed
in tumor board and may not be considered bulky.

- Has a known history of active TB (Bacillus Tuberculosis).

- Other life-threatening illness that is expected to impact life expectancy within 3
years.

- Hypersensitivity to pembrolizumab, epacadostat or any of its excipients.

- Has a known additional malignancy that was diagnosed within the last five years that
is either progressing or requires active treatment. Exceptions include basal cell
carcinoma of the skin or squamous cell carcinoma of the skin that has undergone
potentially curative therapy or in situ cervical cancer, or in a broader sense is not
felt to impact life-expectancy.

- Has active autoimmune disease that has required systemic (large physiologic dose)
treatment in the past year (i.e. with use of disease modifying agents, corticosteroids
or any other immunosuppressive drugs). Replacement therapy (eg., thyroxine, insulin,
or physiologic corticosteroid replacement therapy for adrenal or pituitary
insufficiency, etc.) is not considered a form of systemic immunosuppressive treatment.

- History of non-infectious pneumonitis requiring steroids or current pneumonitis

- Has an active viral infection requiring systemic therapy.

- Has a history or current evidence of any condition, therapy, or laboratory abnormality
that might confound the results of the trial, interfere with the subject's
participation for the full duration of the trial, or is not in the best interest of
the subject to participate, in the opinion of the treating investigator.

- Has known psychiatric or substance abuse disorders that would interfere with
cooperation with the requirements of the trial.

- Is pregnant or breastfeeding, or expecting to conceive or father children within the
projected duration of the trial, starting with the pre-screening or screening visit
through 120 days after the last dose of trial treatment.

- Has a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies).

- Has known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA
[qualitative] is detected).

- Has received a live vaccine within 30 days of planned start of study therapy.

- Allogeneic organ or stem cell transplant

- History of interstitial lung disease (ILD)/pneumonitis requiring treatment with
steroids and patients with active ILD/pneumonitis

Note: Seasonal influenza vaccines for injection are generally inactivated flu vaccines and
are allowed; however, intranasal influenza vaccines (e.g., Flu-Mist®) are live attenuated
vaccines, and are not allowed.