The direct molecular analysis of metastatic precursor cells in breast cancer: A chance for a better understanding of metastasis and for personalised medicine.

The search for disseminated cancer cells has become a routine procedure in many clinical centres since the pioneering work of Riethmüller and Schlimok was published in the mid 1980s. Until today, clinical studies have mostly focused on the prognostic role of disseminated cancer cells that can be detected in bone marrow samples before manifestation of metastasis. As a more recent development, the field is increasingly concentrating on the prognostic information provided by tumour cells circulating in the peripheral blood instead of analysing the nature of disseminated tumour cells that have successfully homed to a new microenvironment and may eventually grow into metastases. This review critically questions that direction and proposes exploiting the unique opportunities provided by the direct molecular analysis of metastatic precursor cells for a better understanding of metastasis, tumour dormancy, therapy target identification, and personalised medicine in an adjuvant therapy setting.