Is There Any Rationale for Detecting Hormone Receptor/HER2 Status with Rebiopsy Without Progression Upfront Metastatic Breast Cancer? with 2 Cases

Alteration of biomarkers is well-documented in breast cancer at locoregional recurrence or metastasis attributed to tumor heterogeneity and change in biology. There is some data about discordance between primary and metastatic sites. At the same time hormone, receptor status can change after neoadjuvant treatment and at the time of recurrence. Metastatic breast cancer without progression or recurrence after the targeted chemotherapy combination for planning maintenance therapy in Human epidermal growth factor receptor 2 (HER2) overexpression positive hormone receptors positive or triple-negative patient after chemotherapy. In guidelines, the time of rebiopsy has no exact time, if the time of biopsy is usually after the progression of the tumor. We presented cases in which we detected different hormone receptor statuses from the beginning without progression and before deciding on maintenance therapy. This subject is important for deciding therapy in the aspect of heterogeneous tumors like breast cancer. The important decision of rebiopsy time is debate. In this aspect, these two cases are important examples for these kinds of patients tumor heterogeneity in breast cancer is one of the most widely known entities. We found that two patients, one of whom was estrogen progesterone receptor negative HER2 3 (+++) at the time of diagnosis and the other who was triple negative at the time of diagnosis, had positive hormone receptors in the re-biopsies without progression. We aimed to discuss the tumor heterogeneity and timing of rebiopsy in breast cancer in the light of two cases.