Stromal tumor-infiltrating lymphocytes and pathologic response to neoadjuvant chemotherapy with the addition of platinum and pembrolizumab in TNBC: a single-center real-world study.

Background: Immunochemotherapy with pembrolizumab has been integrated into clinical practice as part of the standard-of-care for non-metastatic triple-negative breast cancer (TNBC) with high risk. We conducted a real-world study in TNBC patients treated with neoadjuvant chemotherapy to compare pathologic complete response (pCR) rates relative to stromal tumor-infiltrating lymphocytes (sTIL) across different regimens: non-carboplatin, carboplatin-, and pembrolizumab-chemotherapy.

Patients and methods: We analyzed a cohort of 450 patients with TNBC who underwent surgery following neoadjuvant chemotherapy between March 2007 and February 2024. Treatment groups included 247 non-carboplatin, 120 carboplatin, and 83 pembrolizumab-chemotherapy recipients. sTIL was evaluated in biopsied samples. Lymphocyte-predominant breast cancer (LPBC) was defined as tumors with high sTIL (≥ 50%).

Results: The pCR rates were 32% in the non-carboplatin-, 57% in the carboplatin-, and 64% in the pembrolizumab-chemotherapy group. Ninety-two patients (20.4%) had LPBC. In LPBC, the pCR rates did not increase with the addition of carboplatin (50.0% in the non-carboplatin and 41.7% in carboplatin) but reached 83.3% with the addition of pembrolizumab and carboplatin. Among the non-LPBC, the pCR rate increased from 26.7 to 61.1% with the addition of carboplatin, but there was no difference in the pCR rate between the carboplatin and pembrolizumab groups (61.1% and 61.2%, respectively).

Conclusions: In LPBC patients, the addition of carboplatin did not result in an elevated pCR rate; however, the addition of pembrolizumab tended to raise the pCR rate. In non-LPBC, the addition of carboplatin significantly increased the pCR rate, while the addition of pembrolizumab did not have the same effect.