Clinical management of metastatic hormone receptor-positive, HER2-negative breast cancer (MBC) after CDK 4/6 inhibitors: a retrospective single-institution study

• Published in: Breast cancer research and treatment Vol. 196; no. 1; pp. 229 - 237
• Main Authors: Choong, Grace M., Liddell, Savannah, Ferre, Roberto A. Leon, O’Sullivan, Ciara C., Ruddy, Kathryn J., Haddad, Tufia C., Hobday, Timothy J., Peethambaram, Prema P., Liu, Minetta C., Goetz, Matthew P., Giridhar, Karthik V.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.11.2022; Springer; Springer Nature B.V
• Subjects: 1-Phosphatidylinositol 3-kinase; Antimitotic agents; Antineoplastic agents; Antineoplastic Combined Chemotherapy Protocols - therapeutic use; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - genetics; Brief Communication; Cancer; Cancer research; Chemotherapy; Cyclin-dependent kinase; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase 6; Cyclin-dependent kinases; Development and progression; Drug therapy; Endocrine therapy; ErbB-2 protein; Female; Fulvestrant; Fulvestrant - therapeutic use; Hormones; Humans; Letrozole - therapeutic use; Medicine; Medicine & Public Health; Metastases; Metastasis; Oncology; Oncology, Experimental; Patients; Phosphatidylinositol 3-Kinases; Protein Kinase Inhibitors; Receptor, ErbB-2 - genetics; Retrospective Studies; Survival; TOR protein; TOR Serine-Threonine Kinases; Metastatic breast cancer; PI3K/mTOR inhibitor; Subsequent lines of therapy; CDK 4/6 inhibitor
• ISSN: 0167-6806; 1573-7217
• DOI: 10.1007/s10549-022-06713-1

Purpose Cyclin-dependent kinase 4/6 inhibitors (CDK4/6is), in combination with endocrine therapy (ET), are standard either in the first (1L) or second-line (2L) setting for the treatment of hormone receptor (HR) positive, HER2-negative metastatic breast cancer (MBC). However, the optimal sequencing of treatments after progression on CDK4/6i remains unknown. We performed a single-institution analysis to identify treatments and outcomes after progression on a CDK4/6i. Methods We identified patients with HR-positive, HER2-negative MBC prescribed a CDK4/6i in the 1L or 2L settings from December 2014 to February 2018 at Mayo Clinic in Rochester, Minnesota. Outcomes were collected through September 30, 2020. Results Palbociclib, in combination with letrozole or fulvestrant, was the most prescribed CDK4/6i. The 1L and 2L CDK4/6i cohorts exhibited comparable overall survival (OS), but progression-free survival (PFS) was longer in the 1L than the 2L cohort [28.2 months (95% CI 19.6–34.9) vs 19.8 months (95% CI 15.7–29.6)]. The most common post-CDK4/6i treatments were PI3K/mTOR inhibitors (PI3K/mTORi), single-agent ET, or chemotherapy. PFS in the 1L CDK4/6i cohort following PI3K/mTORi was 8.5 months (95% CI 5.5 months—NE), single-agent ET was 6.0 months (95% CI 3.3–14.0 months), and chemotherapy PFS was 5.4 months (95% CI 3.3 months—NE). Conclusions Following progression on a CDK 4/6i, mPFS was short, with similar PFS times comparing chemotherapy and ET, with slightly longer PFS for targeted strategies (PI3K/mTOR). These results highlight a major need to better understand the mechanisms of CDK4/6i resistance and identify new therapeutic strategies for these patients.