Our retrospective study suggests that the ANNAB regimen may be a promising therapeutic approach for patients with relapsed SCLC who have failed second-line therapy. Compared to anlotinib alone, treatment with ANNAB resulted in a significantly longer median PFS of 6.0 months and a median OS of 10.0 months at the cutoff date. These findings are particularly encouraging considering the poor prognosis of patients with relapsed SCLC, especially those with primary platinum-resistant disease (70.8% of our study population). In a real-world analysis of patients receiving various third-line regimens, the ORR was only 21.3%, and the median OS was 4.4 months[14]. Notably, this is the first retrospective study to evaluate the efficacy and safety of the combination therapy of nab-paclitaxel and anlotinib for the treatment of relapsed SCLC in the third-line setting.
The ANNAB regimen was demonstrated to be well-tolerated in this study. Only one patient experienced grade 3 hematologic toxicity. The incidence of non-hematologic AEs observed was consistent with findings from previous studies investigating similar treatments and other treatment indications for these medications. Overall, the combination regimen did not appear to increase the severity of adverse events.
For patients with relapsed SCLC who have undergone two prior treatment regimens, the National Comprehensive Cancer Network (NCCN) guidelines offer limited standard treatment recommendations. Pembrolizumab, an anti-programmed cell death protein 1 (PD-1) monoclonal antibody, has shown an ORR of 19.3% in SCLC patients who have received two or more prior chemotherapy regimens [15]. However, it should be borne in mind that this study involved a small sample size, and pembrolizumab was not approved for first-line extensive-stage SCLC (ED-SCLC) due to negative results in the KEYNOTE-604 trial[16]. Nivolumab, another PD-1 monoclonal antibody, has been FDA-approved as a third-line treatment option, demonstrating an ORR of 11.9%[17]. Unfortunately, nivolumab also failed to demonstrate efficacy in first-line and second-line treatment settings for SCLC, leading its manufacturer to withdraw these treatment indications [18, 19].
In China, anlotinib has been established as a standard recommended treatment option for the third-line treatment of SCLC. A phase 2 study demonstrated that anlotinib resulted in a prolonged PFS of 3.4 months and OS of 2.4 months compared to placebo, with a manageable AE profile. However, the ORR observed with anlotinib monotherapy was only 4.9%. This limited efficacy, particularly for patients with a PS of 0–1, highlights the need for exploring more effective treatment strategies.
Compared to conventional paclitaxel, nab-paclitaxel has been shown in preclinical studies to effectively reach the tumor microenvironment, likely due to its unique pharmacokinetic profile. Clinical trials have demonstrated the antitumor activity of nab-paclitaxel in various solid tumors, including advanced NSCLC[20]. However, data for SCLC is limited, with most studies focusing on second-line therapy. A single-phase 2 study from Italy investigated nab-paclitaxel (100mg/m2 on days 1, 8, and 15 every 4 weeks) as a second-line therapy for SCLC. The study reported an ORR of 8% in the refractory group and 14% in the sensitive group[21]. While the primary endpoint of ORR was not met, nab-paclitaxel demonstrated modest antitumor activity with a tolerable safety profile. A retrospective study from Japan evaluated nab-paclitaxel (75-100mg/m2 on days 1, 8, and 15 every 4 weeks) as a second-line therapy and reported an ORR of 29.4% with manageable adverse events[10]. Overall, these findings suggest that nab-paclitaxel may have some efficacy for relapsed SCLC, particularly in the second-line setting.
Limited data exists regarding the use of nab-paclitaxel as a third-line therapy for SCLC. Wang et al. reported an ORR of 24.3% with nab-paclitaxel administered at a dose of 130mg/m² on days 1 and 8 of a 21-day cycle in this setting. However, the median PFS was only 5.0 months, and the median OS was 9.0 months in their study [22]. Similarly, Kim et al. observed a 33% ORR with nab-paclitaxel monotherapy as a third-line treatment for relapsed or refractory SCLC, but this study included a small sample size of only nine patients who received 100mg/m² of nab-paclitaxel on days 1, 8, and 15 of a 28-day cycle[23]. In conclusion, while nab-paclitaxel monotherapy appears to demonstrate modest efficacy and tolerability in the third-line treatment of SCLC, further investigation is warranted due to the limited data available, particularly from larger, well-designed clinical trials.
Unlike most studies investigating nab-paclitaxel in lung cancer, our study employed a higher dose of 260mg/m² administered every 3 weeks, which aligns more closely with dosing regimens used in breast cancer. This approach reflects the absence of standardized guidelines for the dosing and schedule of nab-paclitaxel specifically for SCLC. Notably, despite the difference in our dosing regimen compared to other studies, the observed toxicity profile of nab-paclitaxel was consistent with previous reports.
Our study has some limitations that should be acknowledged. First, its retrospective design and single-center nature limit the generalizability of the findings. Second, the lack of standardized dosing and schedule for nab-paclitaxel in SCLC, as evidenced by the variations observed across different studies, necessitates further investigation through randomized controlled trials to establish optimal treatment regimens. Additionally, the study population was exclusively Chinese, highlighting the need for multicenter trials with broader patient demographics. Finally, a randomized prospective study is warranted to definitively address the questions raised by our findings.