Inclusion Criteria:

          -  Postmenopausal women age ≥18 years

          -  Histologically confirmed operable or inoperable invasive breast carcinoma

          -  Candidate for neoadjuvant treatment and considered appropriate for endocrine therapy

          -  Willingness to undergo breast surgery after neoadjuvant treatment and to provide three
             mandatory tumor samples

          -  Documented estrogen receptor (ER)-positive tumor in accordance to American Society of
             Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines (Allison et
             al.2020), assessed locally and defined as ≥1% of tumor cells stained positive on the
             basis of the most recent tumor biopsy

          -  Documented progesterone receptor status (positive or negative) as per local assessment

          -  Documented human epidermal growth factor receptor-2 (HER2)-negative tumor in
             accordance to 2018 ASCO/CAP guidelines (Wolff et al. 2018), assessed locally on the
             most recent tumor biopsy

          -  Ki67 score ≥5% analyzed centrally or locally

          -  Eastern Cooperative Oncology Group Performance Status 0-1

          -  Adequate organ function

        Exclusion Criteria:

          -  Stage IV (metastatic) breast cancer

          -  Inflammatory breast cancer (cT4d)

          -  Bilateral invasive breast cancer

          -  History of invasive breast cancer, ductal carcinoma in situ or lobular carcinoma in
             situ and other malignancy within 5 years prior to screening

          -  Previous systemic or local treatment for the primary breast cancer currently under
             investigation

          -  History of any prior treatment with aromatase inhibitors (AIs), tamoxifen, selective
             estrogen receptor down regulator, or cyclin-dependent kinase 4 and 6 inhibitors

          -  Major surgery within 4 weeks prior to randomization

          -  Known clinically significant history of liver disease consistent with Child-Pugh Class
             B or C, including hepatitis

          -  Other severe acute or chronic medical or psychiatric condition or laboratory
             abnormality that may increase the risk associated with study participation or
             investigational product administration or may interfere with the interpretation of
             study results and, in the judgment of the investigator, would make the patient
             inappropriate for entry into this study

          -  History of allergy to anastrozole, or palbociclib or any of its excipients

          -  Known issues with swallowing oral medication

          -  History of documented hemorrhagic diathesis, coagulopathy, or thromboembolism

          -  Active cardiac disease or history of cardiac dysfunction

          -  Current treatment with medications that are well known to prolong the QT interval

          -  Active inflammatory bowel disease or chronic diarrhea, short bowel syndrome, or major
             upper gastrointestinal surgery including gastric resection

          -  Treatment with strong CYP3A4 inhibitors or inducers within 14 days or 5 drug
             elimination half-lives prior to randomization

          -  Known HIV infection

          -  Serious infection requiring oral or IV antibiotics, or other clinically significant
             infection within 14 days prior to screening

          -  Any serious medical condition or abnormality in clinical laboratory tests that, in the
             investigator's judgment, precludes the patient's safe participation in and completion
             of the study