ICK-breast is a prospective, multicentric, non-interventional investigator-initiated trial (IIT) that aims to investigate the prognostic value of CRP kinetics in early and advanced or metastatic triple negative breast cancer (TNBC) under immune checkpoint inhibitor (ICI) therapy on pathological complete response (pCR) and event-free survival in early TNBC patients, and objective response rate (ORR), progression-free survival (PFS) and overall survival (OS) in advanced or metastatic TNBC.

Immunotherapy, which involves activating the body's immune system for cancer treatment, has already been widely incorporated into the standard care of breast cancer patients with early and metastatic triple-negative breast cancer (TNBC).

This study aims to investigate how inflammatory markers such as C-reactive protein (CRP) change during and after immunotherapy. Study findings from other tumor types (kidney, lung, bladder) suggest that immunotherapy is particularly effective when a mild inflammatory response is triggered in the body. The investigators want to examine this using CRP measurement. CRP measurement can easily be integrated into clinical routine as it only requires a blood sample. And since the patients already need a blood draw for chemotherapy, CRP measurement can be performed directly from the blood sample.

The goal of this prospective study is to determine whether changes in CRP levels in the blood can predict the disease progression or response to immunotherapy.

Inclusion Criteria:

• women ≥ 18 years of age
• histologically proven early or advanced or metastatic invasive breast cancer irrespective of therapy line
• ER-negative and progesterone receptor (PR)-negative and human epidermal growth factor receptor 2 (HER2)-negative (IHC 0-2+, Fluorescence In Situ Hybridization (FISH) neg.)
• patients with advanced or metastatic disease must be programmed cell death ligand 1 (PD-L1)-positive (IC ≥ 1 or combined positive score (CPS) ≥ 10) in the experimental group
• planned ICI therapy in combination with chemotherapy in the experimental group
• written informed consent into ICK-breast

Exclusion Criteria:

• ER-positive or PR-positive
• HER2-positive (IHC 2+, FISH pos or IHC 3+)
• any systemic breast cancer therapy before inclusion into the trial for early breast cancer patients
• any ICI therapy before inclusion into the trial
• pregnant or lactating patients
• inadequate general condition (not fit for chemotherapy)

225 patients will be included in the study after written informed consent. Of 75 patients in the control group, which will undergo chemotherapy of physician's choice, 50 patients will be diagnosed with early TNBC and 25 patients will be diagnosed with advanced or metastatic TNBC.

Of 150 patients in the experimental group, which will undergo chemotherapy in combination with ICIs, 100 patients will be diagnosed with early TNBC and 50 patients will be diagnosed with advanced or metastatic TNBC.