Abstract PD7-09: A phase 1/1b study of LSZ102, an oral selective estrogen receptor degrader (SERD), in combination with ribociclib in patients with estrogen receptor-positive (ER+) advanced breast cancer (ABC) who had progressed after endocrine therapy (ET)

Mutations in the ESR1 gene (ESR1m) are important mechanisms of resistance to endocrine therapy in estrogen receptor-positive advanced breast cancer and have been recognized as a prognostic and predictive biomarker as well as a potential therapeutic target. However, the prevalence of ESR1m in real-world patients has not been adequately described. Therefore, we sought to evaluate the prevalence of ESR1m in metastatic samples from Brazilian patients with estrogen receptor-positive (ER+) advanced breast cancer previously treated with endocrine therapy. The presence of ESR1m was evaluated in formalin-fixed paraffin-embedded (FFPE) breast cancer tissue using real-time quantitative polymerase chain reaction (RT-qPCR). Mutations in codons 380, 537, and 538 of the ESR1 gene were analyzed. Out of 77 breast cancer samples, 11 (14.3%) showed mutations in the ESR1 gene. ESR1m were detected in a variety of organs, and the D538G substitution was the most common mutation. In visceral metastasis, ESR1m were detected in 25% (8/32) of the samples, whereas in nonvisceral metastasis, ESR1m were detected in 6.7% (3/45) of the samples. The odds of a sample with visceral metastasis having an ESR1 mutation is 4.66 times the odds of a sample of nonvisceral metastasis having an ESR1 mutation (95% CI: 1.13–19.27; p value = 0.0333). Our study indicates that the prevalence of ESR1m in samples from Brazilian patients with metastatic ER+ breast cancer is similar to that described in patients included in clinical trials. We observed an association of ESR1m with visceral metastasis.

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Plasma ESR1 Mutations and the Treatment of Estrogen Receptor–Positive Advanced Breast Cancer

Journal of Clinical Oncology ◽

10.1200/jco.2016.67.3061 ◽

2016 ◽

Vol 34 (25) ◽

pp. 2961-2968 ◽

Cited By ~ 336

Author(s):

Charlotte Fribbens ◽

Ben O’Leary ◽

Lucy Kilburn ◽

Sarah Hrebien ◽

Isaac Garcia-Murillas ◽

...

Keyword(s):

Breast Cancer ◽

Estrogen Receptor ◽

Advanced Breast Cancer ◽

Metastatic Breast ◽

Advanced Breast ◽

Phase Iii ◽

Wild Type ◽

Estrogen Receptor Positive ◽

Esr1 Mutations ◽

The Impact

Purpose ESR1 mutations are selected by prior aromatase inhibitor (AI) therapy in advanced breast cancer. We assessed the impact of ESR1 mutations on sensitivity to standard therapies in two phase III randomized trials that represent the development of the current standard therapy for estrogen receptor–positive advanced breast cancer. Materials and Methods In a prospective-retrospective analysis, we assessed ESR1 mutations in available archived baseline plasma from the SoFEA (Study of Faslodex Versus Exemestane With or Without Arimidex) trial, which compared exemestane with fulvestrant-containing regimens in patients with prior sensitivity to nonsteroidal AI and in baseline plasma from the PALOMA3 (Palbociclib Combined With Fulvestrant in Hormone Receptor–Positive HER2-Negative Metastatic Breast Cancer After Endocrine Failure) trial, which compared fulvestrant plus placebo with fulvestrant plus palbociclib in patients with progression after receiving prior endocrine therapy. ESR1 mutations were analyzed by multiplex digital polymerase chain reaction. Results In SoFEA, ESR1 mutations were found in 39.1% of patients (63 of 161), of whom 49.1% (27 of 55) were polyclonal, with rates of mutation detection unaffected by delays in processing of archival plasma. Patients with ESR1 mutations had improved progression-free survival (PFS) after taking fulvestrant (n = 45) compared with exemestane (n = 18; hazard ratio [HR], 0.52; 95% CI, 0.30 to 0.92; P = .02), whereas patients with wild-type ESR1 had similar PFS after receiving either treatment (HR, 1.07; 95% CI, 0.68 to 1.67; P = .77). In PALOMA3, ESR1 mutations were found in the plasma of 25.3% of patients (91 of 360), of whom 28.6% (26 of 91) were polyclonal, with mutations associated with acquired resistance to prior AI. Fulvestrant plus palbociclib improved PFS compared with fulvestrant plus placebo in both ESR1 mutant (HR, 0.43; 95% CI, 0.25 to 0.74; P = .002) and ESR1 wild-type patients (HR, 0.49; 95% CI, 0.35 to 0.70; P < .001). Conclusion ESR1 mutation analysis in plasma after progression after prior AI therapy may help direct choice of further endocrine-based therapy. Additional confirmatory studies are required.

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