Individualized treatment of HER2-positive breast cancer patients with lung metastasis using a circulating tumor cell drug sensitivity test: a case report

Breast cancer is a leading cause of tumor-related death in women worldwide. Despite treatment advances, survival from metastatic breast cancer is still not satisfactory. Therefore, timely detection of effective treatment is crucial. Changes in receptor status have been reported between primary tumors and metastases. These were mainly due to the changes in the molecular profiles of breast cancer and the heterogeneity within the tumor. Recent studies have suggested that circulating tumor cells (CTCs) can aid prognostic monitoring and guide individualized treatment by assessing chemotherapy sensitivity. Here, we described two cases of HER2-positive breast cancer patients with lung metastasis using CTC drug sensitivity test for individualized treatment. The results suggest that CTC drug sensitivity test demonstrates good value in guiding individualized treatment. Furthermore, the CTC drug sensitivity test results were found to align well with the histopathological results and the patients’ prior tumor resistance information. These observations preliminarily showcase the potential of CTCs to predict metastatic lesions and to identify effective treatments, especially when histopathology is unavailable. In summary, our case report is the first to evaluate CTC drug sensitivity testing in advanced breast cancer, showing its clinical value and feasibility for personalized therapy, and suggests its broad development prospects in the future. However, further research is needed to validate its reliability.