• The patient has signed and dated the informed consent form (ICF) and it has been obtained before conducting any specific procedure for the study.

• Female or male BC patients of ≥ 18 years of age.

• Permission to access archived tumor tissue sample (either from primary breast tumor or a metastatic lesion, preferably the most recent one) for biomarker analysis. Not having archived tissue is not a reason to exclude the patient from enrollment.

• Paired tumor biopsies, pre-treatment and on-treatment, for pharmacodynamic analysis are not compulsory and will be obtained as per investigator judgement and patient decision. However, patients and investigators are encouraged to obtain them if the patient has easily accessible disease like skin or superficial lymph nodes. Ideally, the same lesion (always in the same organ) should be biopsied before treatment and on treatment whenever possible. It is allowed to use archived biopsies as pre-treatment samples, obtained after ending the previous systemic treatment).

• The lesion accessible for biopsy may not be the only target lesion and should not be located in a previously irradiated field (unless this index lesion has PD ≥ 20% post-radiation).

• Histologically confirmed TNBC that is either locally recurrent, inoperable and cannot be treated with curative intent or is metastatic:

∙ Documented Hormone Receptor (HR) negative BC based on local laboratory determination on the most recent tumor biopsy. HR negative defined as \< 1% positive cells by immunohistochemistry (IHC) for estrogen receptor (ER) and progesterone receptor (PgR).

‣ Documented Human Epidermal Growth Factor Receptor 2 (HER2) negative BC based on local laboratory determination on the most recent tumor biopsy. HER2 negative tumor is determined according to recommendations of the applicable American Society of Clinical Oncology (ASCO)/ College of American Pathologists (CAP) guidelines available.

‣ Patients are eligible for the study irrespectively of BRCA1/2 mutational status. It is not required to have the analysis performed before the study inclusion.

• Patients should be eligible to receive gemcitabine and carboplatin as the following line of therapy. No more than 1 previous line of systemic therapy for the advanced disease is allowed:

∙ Those patients with PD during or within 6 months after completing the (neo)adjuvant treatment are allowed to be included in the study and are considered for second-line group of patients.

‣ Prior therapy with immuno-checkpoint inhibitors (ICIs) either in the metastatic setting (as first-line therapy) or in the (neo)adjuvant setting is allowed.

‣ Previous treatment with platinum-derived agents in early-stage setting is allowed if the platinum-free interval is at least of 12 months.

‣ Prior therapy with PARP inhibitors is allowed.

• Documented progressive disease (i.e. biopsy sample, pathology or imaging report) from the last treatment.

• Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 1.

⁃ Patients must have at least one measurable lesion that can be accurately assessed at baseline and is suitable for repeated assessment by CT scan, MRI, plan X-ray or physical examination. Clinical lesions will only be considered measurable when they are superficial and ≥ 10mm in diameter as assessed using callipers (e.g. skin nodules). Patients with bone-only disease must have a lytic or mixed (lytic + blastic) lesion, which has not been previously irradiated and can be accurately assessed by CT scan/MRI according to RECIST version 1.1 (with a component of soft tissue mass).

⁃ Adequate organ and bone marrow function defined as follows:

• Absolute Neutrophil Count (ANC) ≥ 1.500/mm3 (1.5x109/L), without previous Granulocyte Colony-Stimulating Factor (G-CSF) within 2 weeks prior to the study treatment.

∙ Platelets ≥ 100.000/mm3 (100x109/L), without previous transfusion within 2 weeks prior to the study treatment.

∙ Hemoglobin ≥ 9 g/dL (90 g/L), without previous transfusion within 28 days before starting with the study treatment.

∙ Serum creatinine ≤ 1.5 x Upper Limit of Normal (ULN) or estimated creatinine clearance ≥ 60 mL/min as calculated using the Cockcroft-Gault formula.

∙ Total serum bilirubin ≤ 1.5 x ULN (≤ 3.0 x ULN if Gilbert´s disease).

∙ Aspartate aminotransferase (AST) and/or Alanine aminotransferase (ALT) ≤ 3.0 x ULN (≤ 5.0 x ULN if liver metastases present).

∙ Alkaline phosphatase ≤ 2.5 x ULN (≤ 5.0 x ULN if bone or liver metastases present).

⁃ Resolution of all acute toxic effects of prior anti-cancer therapy or surgical procedures to NCI CTCAE v5.0 Grade ≤ 1 (except alopecia or other toxicities not considered a safety risk for the patient at investigator's discretion). In case of immune-related toxicities, adequately resolved to Grade 1 or non-persistent Grade 2 AEs with the recommended measures by the current guidelines.

⁃ Patients testing positive for human immunodeficiency virus (HIV) are NOT excluded from this study, but HIV-positive patients must meet ALL the following criteria:

• Have CD4+ T-cell (CD4+) counts ≥ 350 cells/µL.

∙ Have not had an opportunistic infection within the past 12 months. Patients on prophylactic antimicrobials can be included in the study.

∙ Should be on stable antiretroviral therapy for at least 4 weeks.

∙ Have an HIV viral load less than 400 copies/mL prior to enrolment.

⁃ Willingness and ability to comply with scheduled visits, treatment plan, laboratory tests and other study procedures.

⁃ Negative serum pregnancy test within 7 days prior to enrolment for premenopausal women, and for women who have experienced menopause onset \< 12 month prior to first dose of therapy..

∙ For premenopausal women: agreement to remain abstinent or use single or combined non-hormonal contraceptive methods that result in a failure rate of \< 1% per year during the treatment period and for at least 7 months after the last dose of study treatment.

‣ For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and to refrain from donating sperm during the same period, as defined below with female partners of childbearing potential or pregnant female partners, men must remain abstinent or use a condom during the treatment period and for at least 6 months after the last dose of carboplatin/gemcitabine to avoid exposing the embryo. Due to the possibility of irreversible infertility with carboplatin/gemcitabine, men receiving these chemotherapies should consult with their doctor regarding conservation of sperm prior to treatment initiation.

⁃ Abstinence is only acceptable if it is in line with the preferred and usual lifestyle of the patient. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or post-ovulation methods) and withdrawal are not acceptable methods of contraception.

⁃ Examples of non-hormonal contraceptive methods with a failure rate of \< 1% per year include tubal ligation, male sterilization, and certain intrauterine devices. Alternatively, two methods (e.g., two barrier methods such as a condom and a cervical cap) may be combined to achieve a failure rate of \< 1% per year. Barrier methods must always be supplemented with the use of a spermicide.