Disseminated tumour cells in bone marrow in experimental colon cancer: metastatic or resident?

Abstract Aim There are conflicting data on the biological and prognostic significance of disseminated tumour cells ( DTC s) in the bone marrow of colorectal cancer patients since bone metastasis is rare in this disease. The study aimed to determine the origin of bone marrow DTC s using human colorectal cancer cells in in vivo and in vitro experimental settings. Method CD 1 nude female mice were xenotransplanted with SW 620 cells (a colorectal cancer cell line isolated from a male patient) injected in the colon wall. At autopsy, the presence of SW 620 in the bone marrow ( BM ), colon and other organs/tissues was recognized by detection of the epithelial marker cytokeratin‐19 ( CK 19) and Y chromosome. In addition SW 620 cells or their conditioned medium were cultured with human BM cells. Results Macroscopically evident CK 19+/ Y ‐chromosome‐positive tumours developed only in five mice receiving SW 620 cells while putative DTC s ( CK 19+) were found in the bone marrow of all treated mice. Most of these CK 19+ cells were Y chromosome negative, only few being Y chromosome positive. In vitro SW 620 cells or their conditioned medium induced CK 19 expression in cultured human bone marrow cells. Conclusion Experimental colorectal cancer can induce the appearance of two distinct CK 19+ cell populations in the bone marrow, one of metastatic origin and the other of murine origin. These findings suggest that bone marrow cells may undergo phenotypic modifications induced by cancer cells.