In the course from cancer diagnosis to metastatic disease, the tumor biology and the mutational profile might change. A meta-analysis (39 clinical studies included) in breast cancer demonstrated that a conversion occurred from positive to negative estrogen receptor status in 22.5%, for progesterone receptor status in 49.4% and for HER2 in 21.3% of cases; the change from negative to positive status occurred for estrogen receptor status in 21.5%, for progesterone receptor status in 15.9% and for HER2 status in 9.5% of cases (Schrijver et al. 2018).
Therefore, to verify that the correct treatment is still indicated, ideally continuous tissue biopsies are required, clearly not feasible in clinical routine. Analysis of the tumor biology and current phenotype of the tumor through exosome diagnostics from blood („liquid biopsy“) could solve the problem of this high unmet medical need.
HER2 targeting therapies are important instruments in treating breast cancer patients and have demonstrated to significantly improve survival. However, only approximately 20-25 % of tumors do express HER2. To qualify for HER2-targeted therapies for breast and gastric cancer, HER2 status is critical which is usually determined by immunohistochemistry using tissue sections. Oncosome.HER2 could determine HER2 status (in blood as liquid biopsy) on exosomes carrying HER2 protein as reflection of the phenotype of the cancer which released the oncosomes. As proof-of-concept, we identified exosomes released from the HER2-positive breast cancer cell line BT474 with ExoMag and counterstained with HER2 antibody.
