This is a single-arm, single-center, open-label trial of pembrolizumab (MK-3475) in subjects with advanced hepatocellular carcinoma as second-line treatment after failure of sorafenib.

Approximately 60 subjects will be enrollment to evaluate the efficacy and safety of pembrolizumab.

Enrollment will begin with all subjects without regard for PD-L1 expression status.

An evaluable specimen for PD-L1 status must be available and confirmed prior to enrollment.

All study subjects will be evaluated every 6 weeks (+/- 7 days) following the date of IP drug adminstration for the first 12 months and every 12 weeks (+/- 7 days) thereafter until progression of disease is documented with radiologic imaging (computed tomography or magnetic resonance imaging).

The primary efficacy endpoint is ORR (objective response rate) per RECIST 1.1.

Each subject will participate in the trial from the time the subject signs the Informed Consent Form (ICF) through the final contact. After a screening phase of up to 28 days, eligible subjects will receive treatment beginning on Day 1 of each 3week dosing cycle for pembrolizumab.

Treatment with pembrolizumab will continue until documented disease progression, unacceptable adverse event(s),intercurrent illness that prevents further administration of treatment, investigators' decision to withdraw the subject, subject withdraws consent, pregnancy of the subject, noncompliance with trial treatment or procedure requirements, subject receives 24 months of pembrolizumab, or administrative reasons requiring cessation of treatment. After the end of treatment, each subject will be followed for 30 days for adverse event monitoring (serious adverse events and events of clinical interest will be collected for 90 days after the end of treatment or 30 days after the end of treatment if the subject initiates new anticancer therapy, whichever is earlier).

Subjects who discontinue after 24months of therapy for reasons other than disease progression or intolerability or who discontinue after attaining a CR may be eligible for up to one year of retreatment after they have experienced radiographic disease progression.

Subjects who discontinue for reasons other than disease progression will have post-treatment follow-up for disease status until disease progression, initiating a non-study cancer treatment, withdrawing consent, or becoming lost to follow-up. All subjects will be followed by telephone for overall survival until death, withdrawal of consent, or the end of the study.

Inclusion Criteria:

1. Be willing and able to provide written informed consent/assent for the trial. The subject may also provide consent for Biomedical Research. However, the subject may participate in the main trial without participating in Biomedical Research.
2. Have histologically or cytologically confirmed diagnosis of HCC (fibrolamellar and mixed hepatocellular/cholangiocarcinoma subtypes are not eligible) based on pathology report.
3. Have Barcelona Clinic Liver Cancer (BCLC) Stage C disease, or BCLC Stage B disease not amenable to locoregional therapy or refractory to locoregional therapy, and not amenable to a curative treatment approach.
4. Have a Child-Pugh class A liver score
5. Has experienced documented objective radiographic or clinical disease progression during first-line sorafenib therapy.
6. Have measurable disease based on RECIST1.1 as determined by investigator.
7. Be willing to provide fresh tissue for biomarker analysis, and, based on the adequacy of the tissue sample quality for assessment of biomarker status. Repeat samples may be required if adequate tissue is not provided. Newly obtained endoscopic biopsy specimens are preferred to archived samples and formalin-fixed, paraffin-embedded (FFPE) block specimens are preferred to slides.

Exclusion Criteria:

1. Is currently participating and receiving study therapy or has participated in a study of an investigational agent and received study therapy or used an investigational device within 4 weeks of the first dose of treatment.
2. Has received sorafenib within 14 days of first dose of study medication.
3. Has had esophageal or gastric variceal bleeding within the last 6 months. All subjects will be screened for esophageal varices, unless such screening has been performed in the past 12 months before first dose of treatment. If varices are present, they should be treated according to institutional standards before starting study treatment.
4. Had a solid organ transplant.
5. Has active autoimmune disease that has required systemic treatment in past 2 years (i.e., with use of disease-modifying agents, corticosteroids, or immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment.
6. Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of trial treatment.
7. Has received locoregional therapy to liver (transcatheter chemoembolization [TACE], transcatheter embolization [TAE], radiation, radioembolization, or ablation) or major surgery to liver or other site within 4 weeks prior to the first dose of study drug. Minor surgery (e.g., simple excision, tooth extraction) must have occurred at least 7 days prior to the first dose of study treatment (Cycle 1, Day 1).

2 year