{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,24]],"date-time":"2026-07-24T05:02:16Z","timestamp":1784869336776,"version":"3.55.0"},"reference-count":60,"publisher":"MDPI AG","issue":"14","license":[{"start":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T00:00:00Z","timestamp":1784678400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100004319","name":"Pfizer Inc.","doi-asserted-by":"crossref","id":[{"id":"10.13039\/100004319","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Cancers"],"abstract":"<jats:p>Background\/Objective: Cyclin-dependent kinase 4\/6 inhibitors (CDK4\/6i) combined with endocrine therapy are the standard first-line treatment for HR+\/HER2\u2212 advanced\/metastatic breast cancer (a\/mBC), yet no head-to-head randomized trials have compared palbociclib, ribociclib, and abemaciclib. This systematic literature review (SLR) aimed to synthesize available real-world evidence (RWE) on the comparative effectiveness of these three CDK4\/6i in the first-line setting. Methods: An SLR was conducted following PRISMA guidelines. Searches of MEDLINE, Embase, Cochrane, and gray literature (January 2015\u2013September 2025) identified RWE studies reporting real-world progression-free survival (rwPFS) and\/or overall survival (OS) for first-line CDK4\/6i regimens. Eligible studies included adults with HR+\/HER2\u2212 a\/mBC receiving palbociclib, ribociclib, or abemaciclib, combined with endocrine-based therapy. Comparative outcomes were summarized qualitatively; study quality was assessed using the Newcastle\u2013Ottawa Scale, ISPOR-AMCP-NPC questionnaire, and ESMO-GROW checklist. Results: From 13,345 records, 39 publications (32 unique studies) were identified, of which 21 were full-text studies meeting inclusion criteria. Most included studies used retrospective cohort designs, and approximately 50% evaluated all three CDK4\/6is. Given the comparative nature of the included studies, quality issues were found to be related to study design and analytical approaches. Several analyses were unadjusted, and reporting of follow-up duration varied across studies, with some analyses providing incomplete follow-up information. Study sample sizes differed substantially across agents, with smaller populations generally reported for ribociclib and abemaciclib. Among the studies reporting rwPFS hazard ratios (HRs), 8\/11 studies showed comparable rwPFS and 5\/6 studies reported comparable OS outcomes between CDK4\/6i regimens. Three full-text studies reported HRs favoring ribociclib or abemaciclib relative to palbociclib; these analyses primarily included populations receiving palbociclib, with smaller comparator cohorts for ribociclib and abemaciclib, as well as varied follow-up times. Conclusions: Most real-world studies included in the SLR suggested similar effectiveness of the three CDK4\/6is in first-line HR+\/HER2\u2212 a\/mBC. Heterogeneity in patient characteristics, definitions of outcomes, follow-up time, sample size, and statistical approach may have important implications on study interpretability.<\/jats:p>","DOI":"10.3390\/cancers18142362","type":"journal-article","created":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T10:48:28Z","timestamp":1784717308000},"page":"2362","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["A Systematic Literature Review of the Effectiveness of CDK 4\/6 Inhibitors for First-Line Treatment of HR+\/HER2\u2212 Advanced\/Metastatic Breast Cancer: A Comparison of Real-World Evidence"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3640-3077","authenticated-orcid":false,"given":"Timothy","family":"Pluard","sequence":"first","affiliation":[{"name":"Hematology and Medical Oncology, St. Luke\u2019s Cancer Institute, Kansas City, MO 64111, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8567-9627","authenticated-orcid":false,"given":"Thomas","family":"Grinda","sequence":"additional","affiliation":[{"name":"Department of Cancer Medicine, Gustave Roussy Institute, 94800 Villejuif, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rodrigo","family":"Dienstmann","sequence":"additional","affiliation":[{"name":"Vall d\u2019Hebron Institute of Oncology (VHIO), Vall d\u2019Hebron Barcelona Hospital Campus, 08035 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marc","family":"Thill","sequence":"additional","affiliation":[{"name":"Department of Gynecology and Gynecologic Oncology, Agaplesion Markus Hospital, 60431 Frankfurt am Main, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Beata","family":"Korytowsky","sequence":"additional","affiliation":[{"name":"Pfizer, Inc., New York, NY 10001, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Connie","family":"Chen","sequence":"additional","affiliation":[{"name":"Pfizer, Inc., New York, NY 10001, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sofiya","family":"Portuhay","sequence":"additional","affiliation":[{"name":"Value & Evidence, EVERSANA<sup>TM<\/sup>, Burlington, ON L7N 3H8, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elizabeth M.","family":"Salvo-Halloran","sequence":"additional","affiliation":[{"name":"Value & Evidence, EVERSANA<sup>TM<\/sup>, Burlington, ON L7N 3H8, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1415-8055","authenticated-orcid":false,"given":"Imtiaz A.","family":"Samjoo","sequence":"additional","affiliation":[{"name":"Value & Evidence, EVERSANA<sup>TM<\/sup>, Burlington, ON L7N 3H8, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9744-7372","authenticated-orcid":false,"given":"Nadia","family":"Harbeck","sequence":"additional","affiliation":[{"name":"Breast Center, Department of Gynecology and Obstetrics and Comprehensive Cancer Center (CCC Munich LMU), LMU University Hospital, 81377 Munich, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1154","DOI":"10.1038\/s41591-025-03502-3","article-title":"Global patterns and trends in breast cancer incidence and mortality across 185 countries","volume":"31","author":"Kim","year":"2025","journal-title":"Nat. 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