Following the PALOMA-3 study results, the combination of palbociclib, a CDK4/6 inhibitor, with fulvestrant, a selective estrogen receptor degrader, has become a standard therapy in women with estrogen receptor-positive (ER+) HER2-negative (HER2−) metastatic breast cancer (MBC). Palbociclib has been shown to increase the progression-free survival (PFS) overall but no predictive biomarker of palbociclib efficacy has been validated so far. We thus evaluated whether early changes of circulating tumor DNA (ctDNA) levels are associated with palbociclib plus fulvestrant efficiency. ER+ HER2− MBC patients were included in a prospective observational cohort before treatment initiation. Tumor response was assessed by radiological evaluation (RECIST v1.1) every 3 months. Plasma samples were collected before treatment (baseline), at day 15 (D15), at day 30 (D30), and at disease progression. We searched for somatic mutations from archived tumor tissues by targeted deep sequencing. For patients with somatic mutations identified, circulating tumor DNA (ctDNA) was tracked using digital droplet PCR. Ratios of ctDNA levels ([D15/baseline] and [D30/baseline]) were then correlated with prospectively registered patient characteristics and outcomes. Twenty-five of the 61 patients enrolled had a somatic mutation testable in plasma (NPIK3CA = 21, NTP53 = 2, NAKT1 = 2). At baseline, 84% of patients had detectable ctDNA levels but ctDNA levels had no prognostic impact on PFS (p = 0.10). Among those patients, ctDNA was still detected in 82% at D15 and 68% at D30. ctDNA clearance observed at day 30 was associated with longer PFS (HR = 7.2, 95% CI = 1.5–32.6, p = 0.004). On the contrary, a [D30/baseline] ctDNA ratio > 1 was associated with a shorter PFS (HR = 5.1, 95% CI = 1.4–18.3, p = 0.02) and all 5 patients with increased ctDNA levels at D30 showed disease progression after 3 months under palbociclib-fulvestrant. Finally, at the time of radiological tumor progression, ctDNA was detected in all patients tested. Our study demonstrates that the efficiency of palbociclib and fulvestrant can be monitored by serial analyses of ctDNA before radiological evaluation and that early ctDNA variation is a prognostic factor of PFS.

中文翻译：

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循环肿瘤 DNA 作为转移性乳腺癌患者对 palbociclib 和氟维司群反应的动态生物标志物

根据 PALOMA-3 研究结果，将 CDK4/6 抑制剂 palbociclib 与选择性雌激素受体降解剂氟维司群联合使用已成为雌激素受体阳性 (ER+) HER2 阴性 (HER2-) 女性的标准疗法转移性乳腺癌（MBC）。Palbociclib 已被证明可提高总体无进展生存期 (PFS)，但迄今为止尚未验证 palbociclib 疗效的预测性生物标志物。因此，我们评估了循环肿瘤 DNA (ctDNA) 水平的早期变化是否与 palbociclib 加氟维司群的效率相关。ER+ HER2- MBC 患者在治疗开始前被纳入前瞻性观察队列。每 3 个月通过放射学评估 (RECIST v1.1) 评估肿瘤反应。在治疗前（基线）、第 15 天（D15）收集血浆样本，在第 30 天 (D30) 和疾病进展时。我们通过靶向深度测序从存档的肿瘤组织中搜索体细胞突变。对于识别出体细胞突变的患者，使用数字液滴 PCR 追踪循环肿瘤 DNA (ctDNA)。然后将 ctDNA 水平的比率（[D15/基线] 和 [D30/基线]）与前瞻性登记的患者特征和结果相关联。入组的 61 名患者中有 25 名具有可在血浆中检测的体细胞突变（NPIK3CA = 21，NTP53 = 2，NAKT1 = 2）。在基线时，84% 的患者可检测到 ctDNA 水平，但 ctDNA 水平对 PFS 没有预后影响（p = 0.10）。在这些患者中，82% 的患者在 D15 和 68% 在 D30 时仍检测到 ctDNA。在第 30 天观察到的 ctDNA 清除与更长的 PFS 相关（HR = 7.2, 95% CI = 1.5–32.6, p = 0.004）。相反，a [D30/基线] ctDNA 比率 > 1 与更短的 PFS 相关（HR = 5.1, 95% CI = 1.4–18.3, p = 0.02），所有 5 名在 D30 时 ctDNA 水平升高的患者在 3 个月后疾病进展palbociclib-氟维司群。最后，在放射肿瘤进展时，在所有测试的患者中检测到 ctDNA。我们的研究表明，在放射学评估之前，可以通过对 ctDNA 的系列分析来监测 palbociclib 和氟维司群的有效性，并且早期 ctDNA 变异是 PFS 的预后因素。在所有测试的患者中检测到 ctDNA。我们的研究表明，在放射学评估之前，可以通过对 ctDNA 的系列分析来监测 palbociclib 和氟维司群的有效性，并且早期 ctDNA 变异是 PFS 的预后因素。在所有测试的患者中检测到 ctDNA。我们的研究表明，在放射学评估之前，可以通过对 ctDNA 的系列分析来监测 palbociclib 和氟维司群的有效性，并且早期 ctDNA 变异是 PFS 的预后因素。