Inclusion Criteria:
1. Sex and age: Female, aged 18 years or older.
2. Histological type: Invasive breast carcinoma of no special type (NST).
3. Triple-negative phenotype, defined by:
* Estrogen receptor (ER) \< 10%,
* Progesterone receptor (PR) \< 10%,
* HER2-negative status according to ASCO/CAP criteria (IHC score 0-1+, or 2+ without amplification by in situ hybridization).
4. High proliferation index: Ki-67 \> 30%.
5. Primary tumor classified as T2, i.e. tumor size between 2 and 5 cm on imaging at diagnosis (mammography, ultrasound, and breast MRI).
6. No regional lymph node involvement or distant metastasis, confirmed by 18F-FDG PET-CT performed prior to neoadjuvant treatment.
7. Completion of the full neoadjuvant chemo-immunotherapy (NCIT) protocol according to the KEYNOTE-522 regimen (≥7 cycles including pembrolizumab).
8. Breast-conserving surgery deemed feasible based on the initial surgical assessment.
9. Radiological complete response (rCR) on post-NCIT breast MRI, associated with a negative vacuum-assisted biopsy (VAB) of the clip-marked tumor bed, confirming the absence of residual invasive or in situ disease.
10. Written informed consent obtained prior to any study-specific procedure.
11. Ability of the patient to comply with the protocol requirements and scheduled follow-up.
12. Affiliation with a national health insurance system, in accordance with French regulations.
Exclusion Criteria:
1. Presence of regional recurrence or metastatic disease at inclusion.
2. History of thoracic, breast, or regional lymph node irradiation, regardless of indication.
3. Invasive lobular carcinoma, excluded due to its different response profile and increased risk of multifocal residual disease.
4. Presence of ductal carcinoma in situ (DCIS) on diagnostic biopsy, or diffuse suspicious microcalcifications on mammography, precluding reliable assessment of complete response.
5. Bilateral breast cancer (except for localized and treated contralateral DCIS), or history of ipsilateral or contralateral invasive breast cancer.
6. Multifocal or multicentric disease detected on imaging (mammography, ultrasound, or breast MRI).
7. Skin involvement or inflammatory breast cancer, identified on imaging or clinical examination.
8. History of malignancy other than breast cancer, unless the disease has been in complete remission for ≥ 5 years and is considered at low risk of recurrence, with the exception of:
* Treated carcinoma in situ of the cervix, endometrium, or colon,
* Melanoma in situ,
* Completely excised cutaneous basal cell or squamous cell carcinoma.
9. Severe or progressive non-malignant disease limiting life expectancy to less than 10 years, in the investigator's judgment.
10. Presence of a high-risk germline mutation predisposing to breast cancer (including BRCA1, BRCA2, or other identified predisposition genes).
11. Participation in another interventional clinical trial within 30 days prior to inclusion.
12. Current pregnancy or breastfeeding.
13. Cognitive impairment, psychiatric disorder, or social situation preventing valid informed consent or adequate understanding of the protocol, as assessed by the investigator.
14. Individuals deprived of liberty or under legal protection (guardianship, curatorship, or similar legal status), in accordance with applicable regulations.
