This is a randomized, open-label study comparing the efficacy and safety of adjuvant sacituzumab tirumotecan (MK-2870) in combination with pembrolizumab compared to treatment of physician's choice (TPC) in participants with triple-negative breast cancer (TNBC) who received neoadjuvant therapy and did not achieve a pathological complete response (pCR) at surgery. The primary objective is to compare sacituzumab tirumotecan plus pembrolizumab to TPC (pembrolizumab or pembrolizumab plus capecitabine) with respect to invasive disease-free survival (iDFS) per investigator assessment. It is hypothesized that sacituzumab tirumotecan plus pembrolizumab is superior to TPC with respect to iDFS per investigator assessment.