Using a high-throughput, qRT-PCR platform, we analyzed the expression of 11 genes (CAV1, CCDN1, CLDN4, EGFR, IGFBP4, KRT19, LOXL2, MLPH, PLAT, SLIT2 and STEAP) in filtered and unfiltered BM, that we and others have found to be expressed by DTCs and breast cancer cells lines, but absent in normal BM [29,32]. The gene discussed is CLDN4; the disease is breast cancer.