Trial to Evaluate Efficacy and Safety of Pembrolizumab and Gemcitabine in HER2-negative ABC

Inclusion Criteria:

1. The patient has signed and dated the informed consent document and it has been obtained before conducting any procedure specifically for the study.
2. Female ≥ 18 years of age on day of signing informed consent.
3. Histological/cytological confirmation of breast cancer with evidence of advanced disease, not amenable to resection or radiation therapy with curative intent.
4. Documented luminal A, luminal B (HER2-negative) or triple negative disease by immunohistochemistry (IHQ) and/or in situ hybridization (FISH/CISH/SISH) based on local testing on the most recent tumour biopsy defined as follows:

   Luminal A: tumour with positive oestrogen receptor (ER) status (≥1% of tumour cells with ER expression) and HER2-negative status (IHQ score 0/1+ or negative by in situ hybridization defined as a HER2/chromosome enumeration probe 17 (CEP17) ratio \< 2 or for single probe assessment a HER2 copy number \< 4) and high progesterone receptor (PgR) (≥ 20% of tumour cells with PgR expression) and low Ki67 (\< 14%).

   Luminal B (HER2-negative): tumour with positive ER status (≥1% of tumour cells with ER expression) and HER2-negative status (IHQ score 0/1+ or negative by in situ hybridization defined as a HER2/CEP17 ratio \< 2 or for single probe assessment a HER2 copy number \< 4) and either low or negative PgR (\< 20% of tumour cells with PgR expression) and/or high Ki67 (≥ 14%).

   Triple negative: tumour with negative hormone receptor status (\<1% of tumour cells with ER and PgR expression) and HER2-negative status (IHQ score 0/1+ or negative by in situ hybridization defined as a HER2/CEP17 ratio \< 2 or for single probe assessment a HER2 copy number \< 4).
5. Have at least one unidimensionally measurable lesion by RECIST 1.1.
6. Patient agrees to the collection of a metastatic tumor sample (biopsy) at the time of inclusion and at progression (whenever possible).
7. Have a performance status of 0, 1 or 2 on the Eastern Cooperative Oncology Group (ECOG) Performance Scale.
8. Demonstrate adequate organ function as follows (all screening labs should be performed within 7 days of study treatment initiation):

   Bone marrow:

   Absolute Neutrophil Count (ANC) ≥ 1,500/mm3 (1.5x109/l) Platelets ≥ 100,000/mm3 (100x109/l) Hemoglobin ≥ 9g/dl or ≥ 5.6 mmol/l without transfusion or erythropoietin (EPO) dependency (within 7 days of assessment)

   Hepatic:

   Serum total bilirubin ≤ 1.5 x Upper Limit of Normal (ULN) Alkaline Phosphatase ≤ 2.5 x ULN Aspartate aminotransferase (AST) (SGOT) and Alanine aminotransferase (ALT) (SGPT) ≤ 2.5 x ULN or ≤ 5 x ULN for patients with liver metastases Albumin ≥ 2.5 g/dl

   Renal:

   Serum creatinine ≤ 1.5 x ULN or creatinine clearance ≥ 60 ml/min for patients with creatinine levels \> 1.5 x ULN

   Coagulation:

   International Normalized Ratio (INR) or Prothrombin Time (PT) ≤ 1.5 x ULN unless patient is receiving 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 patient is receiving anticoagulant therapy as long as PT or PTT is within therapeutic range of intended use of anticoagulants.
9. Prior treatment with anthracyclines and taxanes (unless clinically contraindicated) and two or more prior lines of hormone therapy in hormone receptor positive disease.
10. At least 3 months life expectancy.
11. Patient of childbearing potential should have a negative urine or serum pregnancy within 72 hours prior to receiving the first dose of study drug/medication. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required.
12. Patients of childbearing potential (see section 4.4. for definition) must be willing to use an adequate method of contraception as outlined in Section 4.4. - Contraception, for the course of the study through 120 days after the last dose of study medication.

    Note: Abstinence is acceptable if this is the usual lifestyle and preferred contraception for the subject.
13. Willingness and ability to comply with scheduled visits, treatment plan, laboratory tests and other study procedures.

Exclusion Criteria:

1. HER2-positive disease by immunohistochemistry or in situ hybridation (FISH-SISH-CISH).
2. Patient is currently participating 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 study drug/medication.
3. Has had a prior anti-cancer monoclonal antibody (mAb) within 4 weeks prior to study day 1 or who has not recovered (i.e., ≤ grade 1 or at baseline) from adverse events due to agents administered more than 4 weeks earlier.
4. Has had prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to study day 1 or who has not recovered (i.e., ≤ grade 1 or at baseline) from adverse events due to a previously administered agent.

   * Note: Patients with ≤ grade 2 neuropathy are an exception to this criterion and may qualify for the study.
   * Note: If patient received major surgery, they must have recovered adequately from the toxicity and/or complications from the intervention prior to starting therapy.
5. Has received prior therapy with an anti-Programmed death-1 (PD), anti-PD-L1, or anti-PD-L2 agent.
6. Has received a live vaccine within 30 days of planned start of study therapy.

   o 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.
7. Has hypersensitivity to pembrolizumab, gemcitabine or any of theirs excipients.
8. Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Patients with previously treated brain metastases may participate provided they are stable (without evidence of progression by imaging for at least four weeks prior to the first dose of trial treatment and all neurologic symptoms have returned to baseline), have no evidence of new or enlarging brain metastases, and are not using steroids for at least 7 days prior to trial treatment. This exception does not include carcinomatous meningitis which is excluded regardless of clinical stability.
9. 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 study drug/medication.
10. Has an active autoimmune disease that has required systemic treatment in the 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.
11. Has a current or prior malignancy within the previous 5 years (other than breast cancer or adequately treated basal cell or squamous cell carcinoma of the skin or in-situ carcinoma of the cervix).
12. Has a history of (non-infectious) pneumonitis that required steroids or current pneumonitis.
13. Has an active infection requiring systemic therapy.
14. Has a known history of active Tuberculosis Bacillus (TB) or Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies) or a known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., hepatitis C virus (HCV) RNA \[qualitative\] is detected).
15. Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the patient's participation for the full duration of the trial, or is not in the best interest of the patient to participate, in the opinion of the treating investigator.
16. Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial.
17. Patient is pregnant or breastfeeding, or expecting to conceive within the projected duration of the trial, starting with the baseline visit through 120 days after the last dose of trial treatment.