| E.1 Medical condition or disease under investigation | 
| E.1.1 | Medical condition(s) being investigated | 
| Female metastasized oestrogen receptor positive and/or progesterone receptor positive breast adenocarcinoma |  | 
| E.1.1.1 | Medical condition in easily understood language | 
| Female hormone receptor-positive metastatic breast cancer |  | 
| E.1.1.2 | Therapeutic area | Diseases [C] - Cancer [C04] | 
| MedDRA Classification | 
| E.1.2 Medical condition or disease under investigation | 
| 
| E.1.2 | Version | 20.0 |  
| E.1.2 | Level | PT |  
| E.1.2 | Classification code | 10006202 |  
| E.1.2 | Term | Breast cancer stage IV |  
| E.1.2 | System Organ Class | 10029104 - Neoplasms benign, malignant and unspecified (incl cysts and polyps) |  | 
| E.1.2 Medical condition or disease under investigation | 
| 
| E.1.2 | Version | 20.0 |  
| E.1.2 | Level | LLT |  
| E.1.2 | Classification code | 10027475 |  
| E.1.2 | Term | Metastatic breast cancer |  
| E.1.2 | System Organ Class | 10029104 - Neoplasms benign, malignant and unspecified (incl cysts and polyps) |  | 
| E.1.3 | Condition being studied is a rare disease | No | 
| E.2 Objective of the trial | 
| E.2.1 | Main objective of the trial | 
| Primary objectives:  Safety run-in stage: determine the recommended phase two dose for the randomised stage
  Randomised stage: to determine efficacy of IMP321 combined with weekly paclitaxel compared to weekly paclitaxel plus placebo in hormone receptor-positive metastatic breast cancer patients
 |  | 
| E.2.2 | Secondary objectives of the trial | 
| Secondary objectives:  to further characterise the anti-tumour activity of IMP321 in combination with weekly paclitaxel in
 terms of clinical responses and clinical outcomes and compare it to placebo
  to examine the safety and tolerability of IMP321 in combination with weekly paclitaxel and compare it to placebo
  to characterise the pharmacokinetic (safety run-in only) and immunogenic properties of IMP321
  to assess the quality of life related to IMP321 compared to placebo
 |  | 
| E.2.3 | Trial contains a sub-study | No | 
| E.3 | Principal inclusion criteria | 
| 1. Able to give written informed consent and to comply with the protocol 2.1 Metastatic oestrogen receptor positive and/or progesterone receptor positive breast adenocarcinoma, histologically proven by biopsy of the primary tumour and/or a metastasis
 3. Female of age 18 years or above
 4. Patients who are indicated to receive first line chemotherapy with weekly paclitaxel
 5.1 All patients of childbearing potential must have a negative highly sensitive pregnancy test at screening and agree to use highly effective method for contraception according to the EU Clinical Trial Facilitation Group guidance from time of study entry until at least 6 months after the last administration of study drug. The partners of patients with childbearing potential must also apply
 contraceptive methods. Patients who are either ,
 o postmenopausal (≥ 60 years of age, or < 60 years of age and amenorrhoeic for 12 months in the absence of chemotherapy, tamoxifen, toremifene, or ovarian suppression with folliclestimulating hormone (FSH) above 40 U/L and oestradiol below 30 ng/L; or if taking tamoxifen or toremifene, and age < 60 years, then FSH and oestradiol in the postmenopausal range), permanently sterilized (e.g., bilateral tubal occlusion, hysterectomy),
 o or otherwise be incapable of pregnancy are not considered to be of childbearing potential
 6. ECOG performance status 0-1
 7. Expected survival longer than three months
 8. Resolution of toxicity of prior therapy to grade < 2 (except for alopecia and transaminases in case of liver metastases)
 9. Evidence of measurable disease as defined by RECIST version 1.1
 10.1 Laboratory criteria:
  Total white cell count ≥ 3 x 10^9/L
  Platelet count ≥ 100 x 10^9/L
  Haemoglobin ≥ 9 g/dL or 5.58 mmol/L
  Absolute Neutrophil Count (ANC) ≥ 1.5 x 10^9/L
  Serum creatinine ≤ 1.5 × ULN
  Total bilirubin ≤ 20 μmol/L, except for familial cholaemia (Gilbert’s disease)
  Serum ASAT and ALAT ≤3 times ULN or ≤ 5 times ULN if liver metastases are present
 |  | 
| E.4 | Principal exclusion criteria | 
| 1. Prior chemotherapy for metastatic breast adenocarcinoma 2. Disease-free interval of less than twelve months from the last dose of
 adjuvant chemotherapy
 3. Prior high-dose chemotherapy requiring hematopoietic stem cell
 rescue
 4.1 Inflammatory carcinoma at time of screening
 5.1 Candidate for treatment with trastuzumab (or other Her2/neu
 targeted agents) or endocrine based therapy according to the applicable
 treatment guidelines
 6.2 Systemic chemotherapy, radiation therapy or any other
 investigational agent within 4 weeks, endocrine therapy within 1 week
 or CDK4/6 inhibitors within 5 times half-life (acc. to SPC) prior to first
 dose of study treatment
 7.1 Symptomatic known cerebral and/or leptomeningeal metastases
 8. Women who are pregnant or lactating
 9. Serious intercurrent infection within 4 weeks prior to first dose of
 study treatment
 10. QTcF >480 ms, family or personal history of long or short QT
 syndrome, Brugada syndrome or known history of QTc prolongation, or
 Torsade de Pointes (TdP)
 11. Uncontrolled electrolyte disorders that can worsen the effects of a
 QTc-prolonging drug (e.g., hypocalcaemia, hypokalaemia,
 hypomagnesemia)
 12.1 Evidence of severe or uncontrolled cardiac disease (NYHA III-IV)
 within 6 months prior to first dose of study treatment including:
 myocardial infarction, severe/unstable angina, ongoing cardiac
 dysrhythmias of NCI CTCAE version 4.03 Grade ≥2, atrial fibrillation ,
 coronary/peripheral artery bypass graft, symptomatic congestive heart
 failure, cerebrovascular accident including transient ischemic attack,
 ventricular arrhythmias requiring medication or symptomatic pulmonary
 embolism
 13. Active acute or chronic infection
 14. Active autoimmune disease requiring immunosuppressive therapy
 15.1 Positive test for HIV
 16.1 Positive test for Hepatitis B (anti–HBc) or C (Patients who are anti-
 HBc+ and HBsAg negative are eligible and are not excluded from
 participation in this study)
 17. Life threatening illness unrelated to cancer
 18. Previous malignancies within the last three years other than breast
 carcinoma, except successfully treated squamous cell carcinoma of the
 skin, superficial bladder cancer, and in situ carcinoma of the cervix
 19. Any current disorder that would impede the patient's ability to
 provide informed consent or to comply with the protocol
 20. Any condition requiring continuous systemic treatment with either
 corticosteroids (>10 mg daily prednisone equivalents) or other
 immunosuppressive medications within 4 weeks prior to first dose of
 study treatment. Inhaled or topical steroids and physiological
 replacement doses of up to 10 mg daily prednisone equivalent are
 permitted in the absence of active autoimmune disease
 21. Past history of severe allergic episodes and/ or Quincke's oedema
 22. Alcohol or substance abuse disorder
 23. Known hypersensitivity to any of the components of the study agents
 24.1 Participation in an interventional clinical study within 4 weeks prior
 to first dose of study treatment, with intervention not covered by
 exclusion criterion 6.2
 25. Unwilling or unable to follow protocol requirements
 26. In the clinical judgment of the Investigator, the patient is unsuitable
 for participation in this study
 27. Persons with any kind of dependency on the Investigator or
 employed by the sponsor or Investigator
 28. Persons held in an institution by legal or official order
 29. Patients with prior organ or stem cell transplantation
 30. Patients having received a live, attenuated vaccine within 4 weeks
 prior to the first administration of study treatment
 31. Patients treated with systemic immune stimulatory agents within 6
 weeks or five half lives
 of the drug prior to first administration of study treatment
 |  | 
| E.5 End points | 
| E.5.1 | Primary end point(s) | 
| Stage 1: to determine DLTs and the recommended phase II dose Stage 2: To determine progression free survival (PFS)
 |  | 
| E.5.1.1 | Timepoint(s) of evaluation of this end point | 
| Radiology assessments in the treatment phase will be every 8 weeks until week 73. It may be performed +/- 3 days prior to that specific radiological assessment during the chemo-immunotherapy phase and +/- 7 days during the maintenance and follow-up phase PFS at Follow-Up Visits every 12 weeks (± 1 week) until PD, start of next line of therapy, withdrawal of consent, loss to follow-up, death from any cause, or the end of the study (whichever occurs first).
 For patients who prematurely discontinue treatment for any reason except PD, PFS Follow-Up Visits will occur every 8 weeks until weeks 73 and every 12 weeks thereafter dependent on the most recent radiological assessment prior to  discontinuation.
 |  | 
| E.5.2 | Secondary end point(s) | 
| Secondary endpoints • To assess overall survival (OS)
 • To assess adverse events according to the current National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) and other safety parameters
 • To assess the time to next treatment (TTNT), objective response rate (ORR) according to RECIST 1.1, time to and duration of response and duration of stable disease
 • To assess the plasma concentration time profile of IMP321 and derived PK parameters
 • To assess the quality of life (QOL)
 • To assess development of anti-drug (IMP321) antibodies (ADA)
 |  | 
| E.5.2.1 | Timepoint(s) of evaluation of this end point | 
| OS: After documented PD, every 12 weeks after enrolment into the trial for the first 2 years and every 24 weeks thereafter (± 4 weeks). Other efficacy parameters (TTNT, ORR, time to and duration of response, duration of stable disease) at same timepoints as PFS and OS.
 
 (S)AEs will be collected from the time of ICF signature until 30 days after last study drug administration, and after this period only when considered (in the opinion of the Investigator) related to study treatment.
 
 PK parameters: run-in stage only at cycle 1 day 2, 3 and 4 and cycle 6 day 16, 17 and 18.
 
 QoL: Chemo-immunotherapy phase visit 1 and visit 16; Maintenance phase visit 31 and visit 37; At end of treatment, visit 43.
 
 ADA: at screening, visit 6, 11, 21, 31, 34, 37, 40 and at end of
 treatment.
 |  | 
| E.6 and E.7 Scope of the trial | 
| E.6 | Scope of the trial | 
| E.6.1 | Diagnosis | No | 
| E.6.2 | Prophylaxis | No | 
| E.6.3 | Therapy | Yes | 
| E.6.4 | Safety | Yes | 
| E.6.5 | Efficacy | Yes | 
| E.6.6 | Pharmacokinetic | Yes | 
| E.6.7 | Pharmacodynamic | Yes | 
| E.6.8 | Bioequivalence | No | 
| E.6.9 | Dose response | No | 
| E.6.10 | Pharmacogenetic | No | 
| E.6.11 | Pharmacogenomic | No | 
| E.6.12 | Pharmacoeconomic | No | 
| E.6.13 | Others | Yes | 
| E.6.13.1 | Other scope of the trial description | 
| Quality of life Immuno-monitoring (on blood cells and soluble Th 1 biomarkers)
 |  | 
| E.7 | Trial type and phase | 
| E.7.1 | Human pharmacology (Phase I) | No | 
| E.7.1.1 | First administration to humans | No | 
| E.7.1.2 | Bioequivalence study | No | 
| E.7.1.3 | Other | No | 
| E.7.1.3.1 | Other trial type description |  | 
| E.7.2 | Therapeutic exploratory (Phase II) | Yes | 
| E.7.3 | Therapeutic confirmatory (Phase III) | No | 
| E.7.4 | Therapeutic use (Phase IV) | No | 
| E.8 Design of the trial | 
| E.8.1 | Controlled | Yes | 
| E.8.1.1 | Randomised | Yes | 
| E.8.1.2 | Open | No | 
| E.8.1.3 | Single blind | No | 
| E.8.1.4 | Double blind | Yes | 
| E.8.1.5 | Parallel group | Yes | 
| E.8.1.6 | Cross over | No | 
| E.8.1.7 | Other | Yes | 
| E.8.1.7.1 | Other trial design description | 
| Run-in stage: open-label. Randomization stage: placebo-controlled double-blind. |  | 
| E.8.2 | Comparator of controlled trial | 
| E.8.2.1 | Other medicinal product(s) | No | 
| E.8.2.2 | Placebo | Yes | 
| E.8.2.3 | Other | Yes | 
| E.8.2.3.1 | Comparator description | 
| Run-in stage: not placebo-controlled. Randomization stage: placebo-controlled double-blind. |  | 
| E.8.2.4 | Number of treatment arms in the trial | 2 | 
| E.8.3 | The trial involves single site in the Member State concerned | No | 
| E.8.4 | The trial involves multiple sites in the Member State concerned | Yes | 
| E.8.4.1 | Number of sites anticipated in Member State concerned | 3 | 
| E.8.5 | The trial involves multiple Member States | Yes | 
| E.8.5.1 | Number of sites anticipated in the EEA | 38 | 
| E.8.6 Trial involving sites outside the EEA | 
| E.8.6.1 | Trial being conducted both within and outside the EEA | No | 
| E.8.6.2 | Trial being conducted completely outside of the EEA | No | 
| E.8.7 | Trial has a data monitoring committee | Yes | 
| E.8.8 | Definition of the end of the trial and justification where it is not the last
                        visit of the last subject undergoing the trial | 
| ; 36 months after last patient first visit (stage 2). Approximately 65 months after first patient first visit in the randomised stage 2.  During this follow up period data on progression-free survival and overall survival will be collected. Additionally, any next line of anti-cancer therapy will be recorded |  | 
| E.8.9 Initial estimate of the duration of the trial | 
| E.8.9.1 | In the Member State concerned years | 5 | 
| E.8.9.1 | In the Member State concerned months | 0 | 
| E.8.9.1 | In the Member State concerned days |  | 
| E.8.9.2 | In all countries concerned by the trial years | 6 | 
| E.8.9.2 | In all countries concerned by the trial months | 6 |