Yıldırım H.Ç.Kutlu Y.Mutlu E.Aykan M.B.Korkmaz M.Yalçın S.Şakalar T.Celayir Ö.M.Kayıkçıoğlu E.Aslan F.Hafızoğlu E.Altıntaş Y.E.Keskinkılıç M.Chalabiyev E.Çelebi A.Dursun B.Kapar C.Özen M.Acar Ö.Dülgar Ö.Kut E.Biter S.Kus F.Almuradova E.Erdoğan A.P.Saray S.Güven D.C.Şimşek E.T.Üskent N.Kemal Y.Çakar B.Açıkgöz Ö.Kılıçkap S.Aksoy S.2024-07-222024-07-22202413419625http://akademikarsiv.cbu.edu.tr:4000/handle/123456789/11567Introduction: Male breast cancer, comprising approximately 1% of all breast cancer cases, often leads to the exclusion of male patients as a criterion in clinical trials. While the efficacy of Cyclin-dependent kinases 4 and 6 (CDK 4/6) inhibitors has been established in metastatic hormone receptor-positive (HR +) and human epidermal growth factor receptor 2-negative (HER2 −) breast cancer in women, limited data exist on their effectiveness in male patients. We aimed to evaluate the efficacy and safety of palbociclib or ribociclib in male patients with breast cancer. Methods: This study is a multicenter, retrospective study. We included male patients with HR + and HER2-metastatic breast cancer who received palbociclib or ribociclib as first-line treatment. Our primary endpoints were progression-free survival (PFS), overall response rates (ORR), and drug-related adverse effects. Results: A total of 46 male patients from 27 institutions were enrolled. The median age at initiation of CDK 4/6 inhibitors was 63.64 ± 13.69 years, with a median follow-up of 21.33 (95% CI 14.92–27.74) months. The ORR were 84% for palbociclib and 76.2% for ribociclib. The mPFS for the entire cohort was 28.06 months (95% CI 18.70–37.42). No significant difference in PFS was observed between palbociclib and ribociclib (mPFS: 24.46 months (95% CI 11.51–37.42) vs 28.33 months (95% CI 14.77–41.88), respectively, p = 0.211). No new adverse events were reported. Discussion: This study demonstrates that palbociclib and ribociclib are effective and safe options for first-line treatment in male patients with HR + /HER2 − metastatic breast cancer. However, further prospective studies are warranted to establish their efficacy in this population. © The Author(s) under exclusive licence to Japan Society of Clinical Oncology 2024.EnglishAgedAminopyridinesAntineoplastic Combined Chemotherapy ProtocolsBreast NeoplasmsBreast Neoplasms, MaleFemaleHumansMaleMiddle AgedPiperazinesPurinesPyridinesReceptor, ErbB-2Retrospective Studiesalanine aminotransferasearomatase inhibitorBRCA1 proteinBRCA2 proteincreatininefulvestrantgonadorelin derivativepalbociclibribociclibaminopyridine derivativeantineoplastic agentepidermal growth factor receptor 2ERBB2 protein, humanpalbociclibpiperazine derivativepurine derivativepyridine derivativeribociclibadultalanine aminotransferase levelanemiaArticleastheniabone metastasiscancer controlcancer recurrencecancer regressionclinical articleclinical featurecohort analysisCommon Terminology Criteria for Adverse Eventscreatinine blood leveldeathdemographicsdiarrheadisease exacerbationdrug dose reductiondrug efficacydrug safetyfirst-line treatmentfollow upgene mutationhormone receptor-positive, HER2-negative breast cancerhumanKaplan Meier methodliver metastasislung metastasismalemale breast cancermedian survival timemetastatic breast cancermulticenter studyneutropeniaoutcome assessmentoverall response rateprogression free survivalQTc intervalresponse evaluation criteria in solid tumorsretrospective studyside effectthrombocytopeniatreatment interruptiontreatment responseTurkey (republic)agedbreast tumorclinical trialfemalemetabolismmiddle agedpathologyArticle10.1007/s10147-023-02460-5