Mapping bone marrow niches of disseminated tumor cells.

Breast cancer cells may disseminate early, before tumor diagnosis. Disseminated tumor cells, or DTCs, reside in the bone marrow, and may persist for years or even decades. Some of these cells may be re-activated to resume aggressive growth, and eventually become overt bone metastases. Recent studies have begun to shed light on this complicated process and revealed multiple steps and intermediate states of colonizing DTCs. However, how cancer-host interactions evolve during this process needs to be further understood. Most of our current knowledge of the bone microenvironment is obtained through studies looking for the hematopoietic stem cell (HSC) niche. Although this long-standing question has not yet been resolved, our search for the HSC niche has resulted in a detailed map of various cell types in the bone marrow. Furthermore, various techniques used to find the HSC niche may also be adapted for finding the cancer cell niche. In this article, we will review the recent progress in both the DTC and HSC areas with a focus on their potential microenvironment niches. We will also discuss how to apply what we have learned from HSC studies to map DTCs in the bone context. We hope to stimulate thoughts and ideas to further elucidate the bone colonization process, and develop potential therapeutic interventions.