Introduction:

Breast cancer accounts for 12.5% of all new annual cancer cases worldwide. Cases classified as HER2-positive tend to proliferate, metastasize, and often lead to relapse. HER2 is one of the most valid tumor markers and is widely used as a diagnostic and prognostic biomarker in metastatic breast cancer (MBC). Thus, analyzing the expression of HER2 on circulating tumor cells (CTCs) can offer a real-time dynamic biomarker for guiding treatment options between endocrine therapy and chemotherapy in advanced breast cancer. Functional assays on CTCs with the HER2 biomarker offer evolving diagnostic opportunities, especially when tissue samples are not accessible or are inadequate.

Methods:

Retrospectively, blood samples from 179 breast cancer patients were analyzed for the presence of CTCs using the OncoDiscover® platform approved by the Drug Controller General of India (CDSCO). The platform consists of an immunomagnetic multi-component system mediated by anti-EpCAM antibodies. The isolated cells were immunostained using the nuclear dye DAPI along with CK18, CD45, and HER2 antibodies. CTCs were identified by the presence of HER2-positive, CK18-positive, DAPI-positive, and CD45-negative staining. Validation of HER2 expression on CTCs was analyzed based on the linear intensity gradients of fluorescence signals. CTCs were termed HER2-negative when weak or no detectable fluorescence signal was observed and HER2-positive when high fluorescence signals were detected.

Results:

Among the cohort of 179 patient samples, 63.68% of samples showed the presence of CTCs, with counts ranging from 1–7 CTCs. Among these, 47.84% of the detected CTCs showed HER2 expression. The mean fluorescence intensity value for HER2 expression in CTCs was found to be 3.23. The observed fluorescence intensity further emphasizes the robustness of CTCs as a viable source for molecular characterization.

Conclusion:

Integration of HER2 analysis on CTCs into the clinical assessment of metastatic breast cancer may offer a non-invasive, real-time strategy for tumor profiling and may help pave the way for more precise and tailored therapeutic interventions.