Human epidermal growth factor receptor 2 (HER2) protein overexpression or gene amplification is an important predictive biomarker for identifying patients with breast cancer, who may benefit from HER2-targeted therapy. However, little is known about the molecular landscape and efficacy of HER2-targeted therapy in patients with HER2-mutated metastatic breast cancer. We analysed the HER2 mutation features of 1184 patients with invasive breast cancer. In addition, a single-arm, prospective, phase-II study (NCT03412383) of pyrotinib was conducted in patient with metastatic HER2 amplification-negative, mutation-positive breast cancer. Peripheral blood was collected from each patient and circulating tumour DNA (ctDNA) sequencing was performed using a 1021 gene panel. HER2 mutations were detected in 8.9% (105/1184) of patients. The HER2 amplification-positive patients had a higher mutation frequency than the HER2 amplification-negative patients (19.5% vs. 4.8%, P < 0.001). A multivariate Cox regression analysis indicated that patients with HER2 mutations had a shorter progression-free survival (PFS) than HER2 wild-type patients (median PFS 4.7 months vs. 11.0 months, hazard ratio 2.65, 95% confidence interval 1.25–5.65, P = 0.011). Ten HER2 amplification-negative, mutation-positive patients who received pyrotinib monotherapy were ultimately included in the efficacy analysis. The median PFS was 4.9 months. The objective response rate (complete response + partial response) was 40.0% and the clinical benefit rate (complete response + partial response + stable disease over 24 weeks) was 60%. In conclusion, a HER2 gene mutation analysis is potentially useful to identify biomarkers of trastuzumab resistance in HER2 amplification-positive patients. Patients with HER2-mutated, non-amplified metastatic breast cancers may benefit from pyrotinib.

Antibody-drug conjugates (ADCs) combine the high specificity of monoclonal antibodies with the high anti-tumor activity of small molecular cytotoxic payloads. The anti-tumor activity of ADCs is mainly achieved by the direct blocking of the receptor by monoclonal antibodies, direct action and bystander effect of cytotoxic drugs, and antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity. ADCs have been used in adjuvant therapy and rescue treatment of human epidermal receptor 2 (HER2)-positive breast cancer, greatly improving the prognosis of breast cancer patients. Several ongoing clinical trials of ADC for breast cancer and other solid tumors proved the potential of ADCs will provide more promising treatment options for patients with malignant tumors. This review introduces the mechanism and latest clinical progress of ADC drugs approved for HER2-positive breast cancer to guide clinical practice and conduct research.

Background Two ongoing prospective randomized trials are evaluating whether omitting axillary lymph node dissection (alnd) in patients with breast cancer (bca) and sentinel lymph node (sln) macrometastases undergoing mastectomy is safe. Determining predictive risk factors for non-sln metastases and developing a model to predict the probability of those patients having non-sln metastases is also important.Methods This retrospective study enrolled 396 patients with bca and 1–2 slns with macrometastases who underwent alnd and mastectomy between January 2012 and December 2016. Factors influencing the non-sln metastases were determined, and a predictive nomogram was formulated. Performance of the nomogram was evaluated by its area under the curve (auc).Results We developed a predictive nomogram with an auc of 0.81 (cross-validation 95% confidence interval: 0.75 to 0.86) that included 4 factors (tumour size, histologic grade, and number of negative slns and axillary lymph nodes on imaging).Conclusions Our predictive nomogram assesses the risk of non-sln metastases in patients with bca and 1–2 sln macrometastases undergoing mastectomy.

Background We performed a retrospective study on the efficacy and safety of sirolimus (an mTOR inhibitor) in hormone receptor (HR)-positive advanced breast cancer and searched for biomarkers to predict its efficacy. Methods All patients with HR-positive metastatic breast cancer treated with sirolimus plus endocrine therapy between December 2017 and July 2018 at the Cancer Hospital, Chinese Academy of Medical Sciences were consecutively and retrospectively reviewed. Mutations in circulating tumour DNA (ctDNA) were assayed for 1021 tumour-related genes via gene panel target capture-based next-generation sequencing. Results Thirty-six patients with metastatic breast cancer treated with sirolimus plus endocrine therapy were included. The progression-free survival (PFS) rates between the sirolimus group and everolimus group were similar, and the median PFS was 4.9 months and 5.5 months, respectively (hazard ratio 1.56, 95% CI 0.86–2.81, P = 0.142). The objective response rate in the 36 patients was 19.4%, and the clinical benefit rate was 41.7%. Lipid metabolism disorder was the most common adverse event (69.4%), and 13.9% of patients had stomatitis. Most (94.4%) adverse events were grade 1–2. Twenty patients (55.6%) underwent ctDNA analysis before receiving sirolimus therapy. For patients who received less than 3 lines of chemotherapy, those with PI3K/Akt/mTOR pathway alterations had a better response to sirolimus than those without alterations, with a median PFS of 7.0 months vs 4.3 months (hazard ratio = 0.01, 95% CI 0.00–0.34, P = 0.010). Conclusions Sirolimus is a potentially effective treatment option for patients with HR-positive advanced breast cancer.