As a specific subtype of breast cancer, Triple-negative breast cancer (TNBC) is associated with worse prognosis and higher tumor aggressiveness than HER2-amplified or hormone receptor positive breast cancers. Circulating tumor DNA (ctDNA), as a non-invasive “liquid biopsy”, is an emerging original blood-based biomarker for early breast cancer diagnosis, monitoring treatment response, and determining prognosis. In TNBC patients, ctDNA has an inherent tendency to characterize tumor heterogeneity and metastasis-specific mutations providing a key alternative to tumor tissue profiling. Several studies have already demonstrated the potential of ctDNA in TNBC patients from early to advanced stages of the disease including diagnosis, therapy decisions and assessment of prognosis. This review provides a critical brief summary of the evidence that gives credence to the utility of ctDNA as a biomarker for its role into clinical management in TNBC.

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Background Pyrotinib, a novel irreversible epidermal growth factor receptor 2 (EGFR)/HER2 dual tyrosine kinase inhibitor, has shown promising antitumor efficacy with tolerable toxicity in HER2‐positive metastatic breast cancer (MBC) in several clinical trials. However, the clinical trials do not usually well reflect the patients in real clinical settings. Despite several small‐sample studies in real world, the data on pyrotinib as first‐line and third‐or‐later‐line treatment and the efficacy comparison of pyrotinib combined with different regimens are still lacking. Therefore, this study aimed to investigate the efficacy and safety of pyrotinib for the HER2‐positive MBC in real world to replenish more comprehensive data. Methods A total of 172 HER2‐positive MBC patients treated with pyrotinib‐based therapy were recruited from multiple centers in nonclinical trial settings from September 2017 to June 2020. Results The median progression‐free survival (mPFS) of 172 patients was 8.83 months. The patients, receiving first‐line pyrotinib treatment, had the longest mPFS (20.93 months) compared with those receiving second‐line (8.67 months, p = 0.0339) and third‐or‐later‐line (7.13 months, p = 0.0075) treatments, respectively. Prior treatment with lapatinib ( p = 0.012) and site of metastasis (visceral vs. nonvisceral) ( p = 0.033) were the independent prognostic factors for PFS. The prior treatment with lapatinib compared with lapatinib‐native treatment (5.96 vs. 10.97 months, p = 0.0036) and those with visceral metastasis compared with nonvisceral metastasis (8.40 vs. 23.70 months, p = 0.0138) had worse mPFS. Among 146 patients evaluated for efficacy, 2.1%, 58.9%, and 32.9% showed complete response, partial response, and stable disease, respectively. Adverse events occurred in 92.4% of the patients with 33.3% Grade 3 and higher adverse events and diarrhea (57.0%), anemia (44.8%), and leukopenia (40.7%) as the most frequent ones. Conclusions Pyrotinib‐containing regimen could effectively treat HER2‐positive MBC with acceptable toxicity, including the patients who progressed after lapatinib treatment and with brain metastasis.