Trilaciclib, a CDK4/6 Inhibitor, in Patients With Early-Stage Triple Negative Breast Cancer

Inclusion Criteria: * Suitability of therapy and patient intends to undergo curative surgery * Documented diagnosis of estrogen receptor (ER)-negative and progesterone receptor (PR)-negative tumor * Primary tumor ≥ 1.5 cm with any nodal status * Provide archival tissue for the baseline tissue sample * ECOG performance status of 0 or 1 * Demonstrates adequate organ function * Research tumor biopsies including at least one on-treatment biopsy (and additional biopsy at baseline, if required) * Participants of child bearing potential must be willing to use 2 forms of contraception during the study and for 6 months following study treatment Exclusion Criteria: * Prior systemic therapies or radiation for current breast cancer * History of invasive malignancy ≤3 years prior to signing informed consent except for adequately treated basal cell or squamous cell skin cancer or in situ cervical cancer * History of breast cancer including ipsilateral ductal carcinoma in situ (DCIS) treated with radiotherapy at any time * Previous exposure to doxorubicin of more than 200 mg/m2 (as lifetime exposure to doxorubicin is not to exceed 450 mg/m2) * For patients who will receive pembrolizumab: * History of active autoimmune disease that has required systemic treatment in past 2 years (i.e., with use of disease modifying agents, corticosteroids, or immunosuppressive drugs). Replacement therapy is not considered a form of systemic treatment * Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drugs * History of (non-infectious) pneumonitis that required steroids or current pneumonitis * Known history of active tuberculosis (Bacillus Tuberculosis) * History of severe hepatic impairment * Uncontrolled ischemic heart disease or uncontrolled symptomatic congestive heart failure (Class II-IV as defined by the New York Heart Association \[NYHA\] functional classification system) * Known history of stroke, cerebrovascular accident, severe/unstable angina, myocardial infarction, or coronary angioplasty/stenting/bypass grafting within 6 months prior to enrollment * Known serious active infection (e.g., human immunodeficiency virus \[HIV\], hepatitis B or C, tuberculosis). * Women who are pregnant or breastfeeding * Participation in other studies involving active treatment with investigational drug(s) * Prior hematopoietic stem cell or bone marrow transplantation