Cancer represents one of the main killers worldwide and early detection, before the clinical manifestation of the tumor has occurred, can help to save lives and minimize side effects of the often aggressive treatment that is given when the cancer has reached a more advanced stage. More than 90% of women diagnosed with breast cancer at the earliest stage survive their disease for at least 5 years compared to around 15% for women diagnosed with the most advanced stage of disease. Therefore it is important that the cancer is diagnosed as early possible. Prevalent screening methods can diagnose the cancer only after it has grown into a tumor. Recent studies suggest that molecular changes related to cancer pathogenesis may appear earlier than actually the cancer is visible in imaging techniques. Tumor cells secrete tumor DNA into the blood which carries similar information as the original tumor in the body and cancer serve as a liquid biopsy which can be obtained at any stage of the cancer. However, it is not known how early, before clinically visible tumor, these molecular changes can be detected in the blood. Furthermore, it is not easy to detect those changes because amount of tumor DNA present at the early stage of the cancer may be very little. Therefore it requires sensitive methods to detected tumor DNA circulating in the blood. Today with advanced techniques such as droplet digital PCR and next generation sequencing it is possible to detect earliest changes in during tumor development by analyzing tumor DNA in the blood. We in this study aim to investigate this concept and would like to investigate whether tumor related molecular changes present in the tumor biopsy can be detected in blood samples of same patients obtained before tumor was diagnosed and if yes how early these changes can be detected. If successful this will help clinicians to diagnose cancer earlier and thereby will help them to design better management for cancer patients.