CIRCADIAN is a prospective randomized clinical trial designed to evaluate the impact of pembrolizumab infusions' time-of-day on pathological complete response (pCR) rate among TNBC patients undergoing neoadjuvant treatment.

Patients will be randomized 1:1 to receive all neoadjuvant pembrolizumab cycles (400 mg every 6 weeks) before versus after noon. Subjects will be stratified based on clinical stage at diagnosis (St. II vs III).

Primary outcome will be pCR rate. As a secondary outcome, we will assess for treatment related toxicity.

For planned exploratory circadian rhythm evaluation, daily body temperature and salivary cortisol variation will be measured before each ICI infusion and the Munich Chronotype Questionnaire (MCTQ) will be applied. To assess for emotional stress, physical exercise habits, stimulating substances use and light exposure, patients will also be subjected to the Distress Thermometer and a lifestyle questionnaire. For planned exploratory biomarker research, tumor infiltrating lymphocytes (TILs) analysis will be performed on the initial diagnostic biopsy and after surgery, on residual tumor (in patients not achieving pCR). Cytokine quantification and bulk RNA sequencing plus flow cytometry studies for immune populations profiling will be performed on peripheral blood, at baseline and before surgery, to check for potential biomarkers of circadian modulation.

Inclusion Criteria:

• Female sex
• Age 18 - 75 years old
• Diagnosed with Stage II or III TNBC and candidates for neoadjuvant treatment with ChT+pembrolizumab after multidisciplinary group discussion.

Exclusion Criteria:

• Patients unable to understand or consent to the study;
• Patients not completing ≥2 cycles of planned neoadjuvant pembrolizumab cycles or ≥50% of planned neoadjuvant ChT cycles;
• Patients under daily ≥10 mg of prednisolone or equivalent

Female